Maud Nouri-Neuville

Mohamed Ben Ammar

François H Cornelis
email: francois.cornelis@aphp.fr

Percutaneous image-guided renal ablations: current evidences for long term oncologic efficacy

The rise in incidentally discovered small renal neoplasms has focused attention on nephron-sparing treatment strategies including partial nephrectomy and percutaneous ablation as well as active surveillance. As all treatment modality, renal ablation has matured technically. Radiofrequency ablation, microwave ablation or cryoablation are now performed in many institutions under imaging guidance. The long-term results allow them to be now recommended as a therapeutic option whatever the patients' condition if complete ablation can reliably be achieved.

Introduction

The increasing annual incidence of renal cell carcinoma (RCC) over the past two decades is primarily due to incidental detection on radiologic imaging [START_REF] Jayson | Increased incidence of serendipitously discovered renal cell carcinoma[END_REF]. Nearly 50% of kidney cancers are now diagnosed incidentally and prior to symptoms or evident metastases in 70-80% of cases [START_REF] Bosniak | Small renal parenchymal neoplasms: further observations on growth[END_REF][START_REF] Homma | Increased incidental detection and reduced mortality in renal cancer--recent retrospective analysis at eight institutions[END_REF]. Patient registries indicate the greatest increase in small (< 4cm), localized renal cancers (T1a) [START_REF] Hollingsworth | Five-year survival after surgical treatment for kidney cancer: a population-based competing risk analysis[END_REF]. These changes in patient presentation have led to modifications in the management of RCC [START_REF] Krokidis | CIRSE Guidelines on Percutaneous Ablation of Small Renal Cell Carcinoma[END_REF]. Most of the small, incidentally discovered, well-marginated renal parenchymal neoplasms grow slowly and are not an immediate threat to patient's life. Active surveillance or less invasive nephron-sparing procedures, including laparoscopic or open partial nephrectomy and percutaneous image-guided ablations, have largely replaced radical nephrectomy for treatment of small renal masses [START_REF] Scosyrev | Renal Function After Nephron-sparing Surgery Versus Radical Nephrectomy: Results from EORTC Randomized Trial 30904[END_REF], especially in patients with comorbidities or poor medical status.

Percutaneous image-guided renal tumor ablations, like any new treatment option, required years of study to demonstrate feasibility and safety [START_REF] Mayo-Smith | Imaging-guided percutaneous radiofrequency ablation of solid renal masses: techniques and outcomes of 38 treatment sessions in 32 consecutive patients[END_REF]. As studies reporting technical success and safety for these minimally invasive techniques accumulated, clinical indications for renal ablation were proposed almost twenty years ago [START_REF] Kunkle | Cryoablation or radiofrequency ablation of the small renal mass : a meta-analysis[END_REF]. Initially, poor surgical candidates due to advanced age, comorbidities or renal insufficiency were thought to represent the optimal patients for ablation [START_REF] Kunkle | Cryoablation or radiofrequency ablation of the small renal mass : a meta-analysis[END_REF][START_REF] Mirza | Management of Small Renal Masses in the Older Adult[END_REF][START_REF] Vetterlein | Small renal masses in the elderly: Contemporary treatment approaches and comparative oncological outcomes of nonsurgical and surgical strategies[END_REF][START_REF] Ljungberg | EAU guidelines on renal cell carcinoma: 2014 update[END_REF]. Recently, the American Society of Clinical Oncology extended the recommendations of percutaneous thermal ablation as a therapeutic option whatever the patients' condition if complete ablation can reliably be achieved [START_REF] Finelli | Management of Small Renal Masses: American Society of Clinical Oncology Clinical Practice Guideline[END_REF]. The objective of this review is to assess the current evidence for longer-term oncologic efficacy after percutaneous ablation of renal neoplasms.

Patient selection

The rationale for treatment of small renal tumors is to achieve local tumor control, as cancer-specific mortality increases with higher-stage disease. Nephron sparing strategies are now p promoted to improve quality of life and life expectancy. According to most recent guidelines on the treatment of RCC (EAU, ESMO, ASCO), partial nephrectomy (PN) is strongly recommended for patients with T1a tumors [START_REF] Krokidis | CIRSE Guidelines on Percutaneous Ablation of Small Renal Cell Carcinoma[END_REF][START_REF] Finelli | Management of Small Renal Masses: American Society of Clinical Oncology Clinical Practice Guideline[END_REF][START_REF] Escudier | Renal cell carcinoma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up[END_REF][START_REF] Katsanos | Systematic review and meta-analysis of thermal ablation versus surgical nephrectomy for small renal tumours[END_REF]. Beside PN, percutaneous ablation is now considered in ASCO guidelines as an option for patients that possess tumors such that complete ablation will be achieved [START_REF] Finelli | Management of Small Renal Masses: American Society of Clinical Oncology Clinical Practice Guideline[END_REF]. ESMO guidelines state that ablation may offer an option in patients with small cortical tumors and age >70 years, high surgical risk, solitary kidney, compromised renal function, hereditary RCC or multiple bilateral tumors [START_REF] Escudier | Renal cell carcinoma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up[END_REF].

However, active surveillance is also a valid option for patients >75 years with significant comorbidities and limited life expectancy [START_REF] Bamias | Current Clinical Practice Guidelines for the Treatment of Renal Cell Carcinoma: A Systematic Review and Critical Evaluation[END_REF]. Indications for percutaneous ablation should therefore be considered in relation to each patient's renal mass characteristics; comorbidity and competing risk profiles; and alternate management strategies, including active surveillance or surgical resection. The benefits and risks of such ablation should be carefully weighed, medical comorbidities, renal mass location and size seem to be associated with complication rates after ablation. A working relationship between an interventional radiologist and urologic kidney surgeon would provide an optimal and safe approach for patients.

Biopsies

A biopsy should be obtained before or at the time of any ablation. Initially performed during the same session as the ablation with the advantage of saving time and being more comfortable for the patient, biopsies are now performed days before the ablation due to the significant proportion of biopsies that have been proved negative (40% for tumors <2cm) or shown a benign lesion (20%) [START_REF] Celtik | Active surveillance for incidental renal mass in the octogenarian[END_REF]. It was argued that hemorrhages or air bubbles occurring after biopsies can affect the subsequent targeting of the tumor. However, performing biopsies before ablation can put constraints on patients who may require readjustment to their anticoagulant or antiplatelet medication. In case of initial biopsy non contributive, a second biopsy, eventually performed during the ablation, has to be attempted and is highly effective with a success rate close to 100% [START_REF] Jeon | Percutaneous Kidney Biopsy for a Small Renal Mass: A Critical Appraisal of Results[END_REF].

Technologies

In recent years, a wide range of ablation modalities have been reported, but the more frequently used in a daily practice are currently radiofrequency ablation (RFA), cryoablation and microwave ablation (MWA).

Radiofrequency ablation (RFA)

The percutaneous application of heat-inducing radiofrequency energy to ablate renal masses was first described by Zlotta et al. in 1997 [18]. This technique is now widely used because relatively cheap, easy to use and to monitor, with low rate of complications (Figure 1). The RF electromagnetic wave (ranged between 9 kHz-87.5 MHz) is emitted by an applicator generating an alternating electric current. This current is converted into heat by ionic agitation and thus Joule effect. Different types of electrodes (straight or deployable) exist allowing a homogeneous distribution of heat within a volume. RF current can be applied in "monopolar" or "bipolar" mode. In monopolar mode, a single electrode (or a single electrode group) is used to deliver current into the tumor, while dispersion plates positioned on the lower limbs complete the electrical circuit. In bipolar mode, the current flows only between two electrodes close to or between the two poles of the same needle, which allows a targeted and more efficient heating in the zone located between the electrodes and a reduced dependence on the electrical conductivity of the tissues. Because of these physical properties, RFA is not recommended in case of implantable electronic devices like pacemakers for example because of the risks of desynchronization. This procedure, although easy to implement, is limited to tumors generally less than 4 cm in maximal diameter. Indeed, two main issues associated with this mechanism limit to effectively treat larger tumors. The vapor, desiccation and carbonization created during the RFA gradually increase the impedance of the tissues to the current. This increase in impedance limits the application of additional current and therefore temperatures stagnate at about 100 ° C. In addition, conduction of the heat is relatively slow in tissues because it is slowed by perfusion and convection ("the heat sink effect"), as well as ventilation. For these reasons, and even if it is possible to use several RF applicators to circumvent these limitations, MWA has been developed more recently.

Cryoablation

Renal cryoablation was firstly reported during a laparoscopic procedure in 1995 [START_REF] Kunkle | Cryoablation or radiofrequency ablation of the small renal mass : a meta-analysis[END_REF][START_REF] Uchida | Percutaneous cryosurgery for renal tumours[END_REF]. The development of smaller and improved ultrasound, CT or MR guidance has led to greater utilization of the percutaneous approach (Figure 2). Cryoablation uses the physical properties of high-pressure gases which, when decompressed at atmospheric pressure, causes temperature drop by Joule-Thomson effect. Indeed, the relation between temperature, pressure and volume of a gas is described by the gas laws: when the volume of the gas increases (the gas expands), often the temperature decrease. In this technique, no gas is released outside the device. The efficiency of this technique is linked to at least five mechanisms produced by the ice formation:

• direct cell death below -40 ° C by rapid formation of intracellular ice crystals, and direct damage to the cell membrane and organelles;

• slower formation of extracellular ice crystals leading to a change in osmolality in the extracellular space and, in turn, dehydration and cell death;

• thrombosis of the blood vessels, interrupting blood flow to the tissues, causing ischemia and cell death;

• the induction of apoptosis, the programmed cell death cascade due to disruption of cell function;

• activation of the immune system by the release of intact tumor antigens, highly immunogenic especially if intracellular.

The perfect visualization of the physical changes caused by freezing whether using CT, MRI or ultrasound seems to be a major advantage of cryoablation [START_REF] Aron | Renal tumor ablation[END_REF][START_REF] Onik | Ultrasound characteristics of renal cryosurgery[END_REF]. This could be useful for monitoring the treatment when the lesion to be treated is close to sensitive organs or structures. Moreover, as pain is mild and recovery rapid after the procedure, percutaneous cryoablation can be carried out under local or general anesthesia [START_REF] Callstrom | Painful metastases involving bone: percutaneous image-guided cryoablation--prospective trial interim analysis[END_REF]. It could be a major advantage for elderly patients or for patients suffering from severe comorbidities which compromised general anesthesia. Another advantage is that there is no denaturing of protein, as in hyperthermic treatment, in the architecture of supporting tissues, particularly urothelial tissue, which is therefore conserved. Cryoablation tend to spare the collecting system in a porcine model [START_REF] Strine | Inadvertent cryoablation of exophytic upper tract urothelial carcinoma without pelvicalyceal involvement[END_REF][START_REF] Janzen | The effects of intentional cryoablation and radio frequency ablation of renal tissue involving the collecting system in a porcine model[END_REF]. However, bleeding and hematuria were most common with cryoablation [START_REF] Atwell | Complications following 573 percutaneous renal radiofrequency and cryoablation procedures[END_REF].

Microwave ablation

Microwave ablation (MWA) is currently mainly used for the treatment of hepatocellular carcinoma [START_REF] Liang | Microwave ablation of hepatocellular carcinoma[END_REF], but few study proposed this technique for treatment of RCCs (Figure 3) [START_REF] Cornelis | Microwave ablation of renal tumors: A narrative review of technical considerations and clinical results[END_REF].

MWA affects directly the water molecules as they are continually realigning under the oscillating effect of the MW field, which effectively increases the kinetic energy and tissue temperature again by Joule effect. Unlike electric currents, MW radiate through all biological tissues, including those with high impedance, such as bones, lungs (filled with gas) and charred or desiccated tissues. This allows the MW to generate a higher heat> 100 ° C continuously. The volume of ablation will depend on the application time. Different generations of MWA systems now exist and each system is characterized by a different combination of antenna diameter (12-17G), number of antennas (1-3), frequency control (915 MHz or 2.45 GHz) and phase, power generated (from 40 to plus 100W) and loss of power between the generator and the tip of the applicator. MWA has several theoretical advantages over RF ablation in producing consistently higher intratumoral temperatures, larger ablation volumes, less ablation time, less dependence on the electrical conductivities of tissue, and energy delivery less limited by the exponentially rising electrical impedance of tumor tissue [START_REF] Cornelis | Microwave ablation of renal tumors: A narrative review of technical considerations and clinical results[END_REF][START_REF] Simon | Microwave ablation: principles and applications[END_REF][START_REF] Wright | Radiofrequency versus microwave ablation in a hepatic porcine model[END_REF][START_REF] Brace | Radiofrequency and microwave ablation of the liver, lung, kidney, and bone: what are the differences?[END_REF].

Patient clinical outcomes and expectable results

The majority of ablation studies are observational and retrospective in nature. Randomized control trials that compare thermal ablation with nephron-sparing surgery or active surveillance have not been performed.

Radiofrequency ablation

Renal RFA studies from 2003 have reported a wide primary efficacy range in the first year (67-100%) [START_REF] Mayo-Smith | Imaging-guided percutaneous radiofrequency ablation of solid renal masses: techniques and outcomes of 38 treatment sessions in 32 consecutive patients[END_REF][START_REF] Salas | Results of radiofrequency kidney tumor ablation: renal function preservation and oncologic efficacy[END_REF][START_REF] Gervais | Radiofrequency ablation of renal cell carcinoma: part 2, Lessons learned with ablation of 100 tumors[END_REF][START_REF] Mylona | Percutaneous radiofrequency ablation of renal cell carcinomas in patients with solitary kidney: 6 years experience[END_REF][START_REF] Zagoria | Oncologic efficacy of CT-guided percutaneous radiofrequency ablation of renal cell carcinomas[END_REF][START_REF] Rouviere | Radiofrequency ablation of renal tumors with an expandable multitined electrode: results, complications, and pilot evaluation of cooled pyeloperfusion for collecting system protection[END_REF][START_REF] Tracy | Durable oncologic outcomes after radiofrequency ablation: experience from treating 243 small renal masses over 7.5 years[END_REF]. Secondary efficacy of RFA reveals considerably higher rates of oncologic control (90-100%) [START_REF] Gervais | Radiofrequency ablation of renal cell carcinoma: part 2, Lessons learned with ablation of 100 tumors[END_REF][START_REF] Tracy | Durable oncologic outcomes after radiofrequency ablation: experience from treating 243 small renal masses over 7.5 years[END_REF][START_REF] Levinson | Long-term oncological and overall outcomes of percutaneous radio frequency ablation in high risk surgical patients with a solitary small renal mass[END_REF][START_REF] Veltri | Percutaneous RF thermal ablation of renal tumors: is US guidance really less favorable than other imaging guidance techniques?[END_REF][START_REF] Salagierski | Percutaneous ultrasound-guided radiofrequency ablation for kidney tumors in patients with surgical risk[END_REF]. Variability of primary efficacy after renal ablation, follow-up schedules and modalities can partially account for these ranges and can be also explained by the very variable follow-up times and tumor sizes treated. During the last 5 years, these results have been confirmed by long-term studies after RFA [START_REF] Balageas | Ten-year experience of percutaneous image-guided radiofrequency ablation of malignant renal tumours in high-risk patients[END_REF][START_REF] Abel | Percutaneous biopsy facilitates modern treatment of renal masses[END_REF][START_REF] Zagoria | Long-term outcomes after percutaneous radiofrequency ablation for renal cell carcinoma[END_REF][START_REF] Psutka | Long-term oncologic outcomes after radiofrequency ablation for T1 renal cell carcinoma[END_REF]. Recently, Zhang et al. evaluated outcomes for tumor stage of T1a 93 (76.2%) or T1b 29 (23.8%) and for a mean follow-up period of 64.9 months (±11.6) (range 9-83 months) [START_REF] Zhang | Prognostic Factors for Long-Term Survival in Patients with Renal-Cell Carcinoma After Radiofrequency Ablation[END_REF]. In total, 5-year cancer-specific survival, 5-year DFS, 5-year recurrence-free survival (RFS), 5-year metastasisfree survival, and 5-year overall survival (OS) of this cohort was 98.3%, 90.8%, 94.2%, 99.2%, and 98.4%, respectively. Other long-term results are also available but with several limitations such as lack of biopsy-proven tumors [START_REF] Levinson | Long-term oncological and overall outcomes of percutaneous radio frequency ablation in high risk surgical patients with a solitary small renal mass[END_REF][START_REF] Ferakis | Long-term results after computed-tomography-guided percutaneous radiofrequency ablation for small renal tumors[END_REF]; or mix of intra-operative and percutaneous image-guided RFA to assess long-term oncologic outcomes as it has been show that outcomes differ between these two approaches [START_REF] Tracy | Durable oncologic outcomes after radiofrequency ablation: experience from treating 243 small renal masses over 7.5 years[END_REF][START_REF] Hui | Comparison of percutaneous and surgical approaches to renal tumor ablation: metaanalysis of effectiveness and complication rates[END_REF][START_REF] Lorber | Long-term oncologic outcomes following radiofrequency ablation with real-time temperature monitoring for T1a renal cell cancer[END_REF].

In RFA, special attention must be observed during patient selection because size and sinus extension of the tumor to be treated can increase the risk of technical failure. Since 2003 it has been reported that RFA is substantially less effective for tumors larger than 4 cm, but is highly effective for tumor smaller than 3cm [START_REF] Gervais | Radiofrequency ablation of renal cell carcinoma: part 2, Lessons learned with ablation of 100 tumors[END_REF][START_REF] Balageas | Ten-year experience of percutaneous image-guided radiofrequency ablation of malignant renal tumours in high-risk patients[END_REF][START_REF] Psutka | Long-term oncologic outcomes after radiofrequency ablation for T1 renal cell carcinoma[END_REF][START_REF] Zhang | Prognostic Factors for Long-Term Survival in Patients with Renal-Cell Carcinoma After Radiofrequency Ablation[END_REF]. For tumors larger than 3.6cm, Zagoria described a risk of recurrence increased by a factor of 2.19 for each additional centimeter [START_REF] Zagoria | Oncologic efficacy of CT-guided percutaneous radiofrequency ablation of renal cell carcinomas[END_REF]. The recurrence-free survival rate was not however influenced by sex, the side or cranio-caudal topography of the tumor. While Zagoria found no significant difference whether the site of the lesion was exophytic, parenchymal, central or mixed, Gervais et al.

showed that only the non-central site of lesions is described as an independent factor of secondary efficacy [START_REF] Gervais | Radiofrequency ablation of renal cell carcinoma: part 2, Lessons learned with ablation of 100 tumors[END_REF]. However, Gervais emphasized that the choice of a size limit for treatment is not unequivocal [START_REF] Gervais | Radiofrequency ablation of renal cell carcinoma: part 2, Lessons learned with ablation of 100 tumors[END_REF]. This group reported a cut-off at 4 cm produced treatment that was 90% complete, while excluding 15% of patients who could have benefited from effective treatment. A cut-off at 5.8 cm would mean 99% of patients could be treated completely, but with a short-term success rate of 63% [START_REF] Gervais | Radiofrequency ablation of renal cell carcinoma: part 2, Lessons learned with ablation of 100 tumors[END_REF]. The reduced efficacy of RFA in large tumors reflects that RFA is susceptible to the cooling effect of flowing blood. Nakasone et al. compared the effects of RFA alone and of RFA combined with occlusion of the arterial blood supply on the coagulation diameter and histological changes in a porcine kidney model. The maximal coagulation diameter was significantly larger with occlusion.

Histological analysis showed preservation of the normal renal parenchymal structure outside the thermal lesion. This study demonstrated that a technique combining RFA and partial occlusion of blood flow may be useful to treat large renal tumors [START_REF] Nakasone | Radiofrequency ablation in a porcine kidney model: effect of occlusion of the arterial blood supply on ablation temperature, coagulation diameter, and histology[END_REF]. Furthermore, Yamakado et al studied feasibility, safety, and therapeutic effects of the combination of embolization and RFA of renal tumors measuring 3.5 cm or larger, mostly with extension into the renal sinus fat. The tumors were embolized selectively before RFA. All tumors remained controlled during a mean follow-up period of 13 months [START_REF] Yamakado | Radiofrequency ablation combined with renal arterial embolization for the treatment of unresectable renal cell carcinoma larger than 3.5 cm: initial experience[END_REF]. However, close and long-term follow-up of patients presenting these risk factors of recurrence (large tumors or sinus extension) may be recommended according with these results. Moreover, other ablation technique, such as cryoablation or MWA, must be considered when RFA procedures cannot be adapted to obtain complete and safe tumor eradication.

Until now, only few studies have compared RFA with partial (PN) or radical nephrectomy (RN). Stern et al doesn't found significant difference in recurrence-free survival at 3 years for T1a tumors treated by these 2 options (37 PN vs 40 RFA) with respective levels of 95.8% and 93.4% [START_REF] Stern | Intermediate comparison of partial nephrectomy and radiofrequency ablation for clinical T1a renal tumours[END_REF]. However, this study included 5 benign masses. Takaki et al [START_REF] Takaki | Radiofrequency ablation versus radical nephrectomy: clinical outcomes for stage T1b renal cell carcinoma[END_REF] reported that overall survival rate was significantly lower in the RF ablation group (n=21) than in the radical nephrectomy group (n=39) (48% vs 97% at 10 years,; P < .009). The RCC-related survival rate (94% with RFA vs 100% with radical nephrectomy at 10 years) and the diseasefree survival rate (88% with RFA vs 84% with radical nephrectomy at 10 years, P = .99) were comparable between the two groups. In a recent meta-analysis, twelve retrospective studies that compared RFA with partial nephrectomy were reviewed [START_REF] Yin | Radiofrequency Ablation Versus Partial Nephrectomy in Treating Small Renal Tumors[END_REF]. Compared with partial nephrectomy, RFA achieves an equal oncological outcome with similar local recurrence rate (4.14% vs 4.10%, RR: 1.18, 95% CI: 0.68, 2.07, P = 0.550) and distant metastases rate (2.76% vs 1.89%, RR: 1.31, 95% CI: 0.70, 2.46, P = 0.686). Additionally, RFA was associated with lower decline of eGFR (-3.90, 95% CI: -6.660, -1.140, P = 0.006), and shorter length of stay (-2.02 days, 95% CI: -2.77, -1.27, P < 0.001). A similar perioperative complication rate was observed either for the overall perioperative complication rate (7.5% vs 6.2%, RR:1.10, 95% CI: 0.64, 1.87, P = 0.740) and the major complication rate (3.7% vs 4.4%, RR: 0.83, 95% CI: 0.43, 1.60, P = 0.579).

Cryoablation

In the largest study to date, Rodriguez et al [START_REF] Rodriguez | Prospective analysis of the safety and efficacy of percutaneous cryoablation for pT1NxMx biopsy-proven renal cell carcinoma[END_REF] reported the outcome of percutaneous cryoablation on 117 pT1a or pT1b biopsy-proven renal cell carcinoma (RCC) in 113 consecutive patients. In this study, technical success was 100% with 7% rate of clinically significant complications and 0% mortality. Seventy percent of patients were discharged on the same day. Efficacy was 98.7% for a median follow-up of 67 weeks (range 7-172). For the subgroup of patients that reached a median follow-up of 2 (n = 59) and 3 years (n = 13), efficacy was 98.3 and 92.3%, respectively and cancer specific survival was 100%. Renal function was not adversely affected.

Compared to RFA, the meta-analysis of Kunkle et al showed that primary efficacy of cryotherapy was better than RFA, with a reoperation rate of 8.5% for RF versus 1.3% for cryotherapy (P < 0.0001). However, this study compiling laparascopic and percutaneous approaches, which could introduce a technical bias. The local tumor progression rate was significantly higher for RFA than for cryoablation (12.9% vs 5.2%, P < 0.0001). Moreover, the frequency of metastases was reported to be lower for cryoablation (1.0%) than for RF (2.5%, P = 0.06) during monitoring. More recently, Atwell et al [START_REF] Atwell | Percutaneous ablation of renal masses measuring 3.0 cm and smaller: comparative local control and complications after radiofrequency ablation and cryoablation[END_REF] have compared the efficacy and complication rates of percutaneous radiofrequency ablation (RFA) and cryoablation in the treatment of 445 renal masses measuring 3.0 cm and smaller. Two hundred fifty-six tumors in 222 patients were treated with RFA (mean tumor size, 1.9 ± 0.5 cm), and 189 tumors in 163 patients were treated with cryoablation (mean tumor size, 2.3 ± 0.5 cm). For biopsyproven RCC, estimated local recurrence-free survival rates at 1, 3, and 5 years after RFA were 100%, 98.1%, and 98.1%, respectively, compared with 97.3%, 90.6%, and 90.6%, respectively, after cryoablation (p = 0.09). There were five (1.1%) technical failures, including one (0.4%) among tumors treated with RFA and four (2.1%) among tumors treated with cryoablation (p = 0.17) but major complications occurred after 4.3% (10/232) of RFAs and 4.5% (8/176) of cryoablation procedures (p = 0.91). Subsequently, authors concluded to similar results in case of ablation of tumors <3cm.

Recently, Caputo et al. compared the outcomes of 31 patients treated by cryoablation (percutaneously and laparoscopically) and 161 partial nephrectomy [START_REF] Caputo | Cryoablation versus Partial Nephrectomy for Clinical T1b Renal Tumors: A Matched Group Comparative Analysis[END_REF]. Tumors were matched for several characteristics including tumor size (4.6 vs 4.3cm; p=0.076). The rate of local recurrence was significantly higher for CA than for PN (p=0.019) but there was no significant difference in cancer-specific mortality (p=0.5) or overall mortality (p=0. [START_REF] Bamias | Current Clinical Practice Guidelines for the Treatment of Renal Cell Carcinoma: A Systematic Review and Critical Evaluation[END_REF] between the CA and PN groups. The total postoperative complication rate was higher for PN than for CA (42% vs 23%; p=0.10). There was no significant difference in percentage eGFR preservation between PN and CA (89% vs 93%; p=0.5). Thompson et al reviewed 1057 PN, 180 RFA, and 187 cryoablation of T1a tumors [START_REF] Thompson | Comparison of partial nephrectomy and percutaneous ablation for cT1 renal masses[END_REF]. In this cohort, local recurrence-free survival was similar among the three treatments (p=0.49), whereas metastases-free survival was significantly better after PN (p=0.005) and cryoablation (p=0.021) when compared with RFA. In addition, 326 patients underwent PN, and 53 patients were managed with cryoablation for T1b tumor. In this cohort, local recurrence-free survival (p=0.81) and metastases-free survival (p=0.45) were similar between PN and cryoablation.

Microwave ablation

In the study of Clark et al. [START_REF] Clark | Microwave ablation of renal parenchymal tumors before nephrectomy: phase I study[END_REF] who gave 10 patients microwave treatment before nephrectomy, histological analysis showed uniform cell death in the ablation zone. Liang et al. [START_REF] Liang | Percutaneous cooled-tip microwave ablation under ultrasound guidance for primary liver cancer: a multicentre analysis of 1363 treatment-naive lesions in 1007 patients in China[END_REF] reported the results of a feasibility study in which 12 patients were treated without remnant or recurrence at a mean follow-up of 11 months. Carrafiello et al. [START_REF] Carrafiello | Singleantenna microwave ablation under contrast-enhanced ultrasound guidance for treatment of small renal cell carcinoma: preliminary experience[END_REF] also performed 12 successful procedures, with a mean follow-up of 6 months [START_REF] Homma | Increased incidental detection and reduced mortality in renal cancer--recent retrospective analysis at eight institutions[END_REF][START_REF] Hollingsworth | Five-year survival after surgical treatment for kidney cancer: a population-based competing risk analysis[END_REF][START_REF] Krokidis | CIRSE Guidelines on Percutaneous Ablation of Small Renal Cell Carcinoma[END_REF][START_REF] Scosyrev | Renal Function After Nephron-sparing Surgery Versus Radical Nephrectomy: Results from EORTC Randomized Trial 30904[END_REF][START_REF] Mayo-Smith | Imaging-guided percutaneous radiofrequency ablation of solid renal masses: techniques and outcomes of 38 treatment sessions in 32 consecutive patients[END_REF][START_REF] Kunkle | Cryoablation or radiofrequency ablation of the small renal mass : a meta-analysis[END_REF][START_REF] Mirza | Management of Small Renal Masses in the Older Adult[END_REF][START_REF] Vetterlein | Small renal masses in the elderly: Contemporary treatment approaches and comparative oncological outcomes of nonsurgical and surgical strategies[END_REF][START_REF] Ljungberg | EAU guidelines on renal cell carcinoma: 2014 update[END_REF][START_REF] Finelli | Management of Small Renal Masses: American Society of Clinical Oncology Clinical Practice Guideline[END_REF][START_REF] Escudier | Renal cell carcinoma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up[END_REF][START_REF] Katsanos | Systematic review and meta-analysis of thermal ablation versus surgical nephrectomy for small renal tumours[END_REF]. Yu et al. [START_REF] Yu | US-guided percutaneous microwave ablation of renal cell carcinoma: intermediate-term results[END_REF] treated 46 patients with 49 RCC nodules (diameter, 0.6-7.7 cm; mean, 3.0 cm) without major complications. In this study, technical effectiveness was achieved in 48 of 49 (98.0%) tumors, and the metastasis-free rate was 100% (46 of 46). The 1-, 2-, and 3-year local tumor progression rates were 4.6%, 7.7%, and 7.7%, respectively. The cancer-specific survival rate was 100% (46 of 46), and 1-, 2-, and 3-year overall survival rates were 100%, 100%, and 97.8%, respectively. The 1-, 2-, and 3-year disease-free survival rates were 95.4%, 92.3%, and 92.3%, respectively. Moreover, as reported for RFA, multivariate analysis showed that tumor number (P = .046), tumor growth patterns (P = .003), and ablation time (P = .04) were independent unfavorable prognostic factors. Recently, Klapperich et al [START_REF] Klapperich | Effect of Tumor Complexity and Technique on Efficacy and Complications after Percutaneous Microwave Ablation of Stage T1a Renal Cell Carcinoma: A Single-Center, Retrospective Study[END_REF] evaluated the midterm oncologic efficacy for 100 T1a tumors (median diameter, 2.6 cm ± 0.8) treated with percutaneous MWA over a median imaging follow-up of 15 months (range, 0-44 months).

Technical success was achieved for all 100 tumors (100%) whatever the complexity. No change in estimated glomerular filtration rate was noted after the procedure (P = .49). There were three (3%) procedure-related complications and six (6%) delayed complications, all urinomas. One case of local tumor progression (1%) was identified 25 months after the procedure. Three-year local progression-free survival, cancer-specific survival, and overall survival were 88%, 100%, and 91%, respectively.

Recently, the meta-analysis of Choi et al showed favorable technical and oncologic outcomes after MWA with low incidence of major complications [START_REF] Choi | Efficacy and Safety of Microwave Ablation for Malignant Renal Tumors: An Updated Systematic Review and Meta-Analysis of the Literature Since 2012[END_REF]. A total of 567 patients carrying 616 malignant renal tumors were included in the meta-analysis. The local tumor recurrence rate was 2.1%. At 1-, 2-, 3-, and 5-year follow-up time points, the cancer-specific survival rate were 99.1%, 98.4%, 97.6%, and 96.9% respectively, while the overall survival rate were 98.3%, 94.9%, 86.8%, and 81.9%. In terms of major complications, a 1.8% incidence was found. Gao et al [START_REF] Gao | Microwave treatment of renal cell carcinoma adjacent to renal sinus[END_REF] studied MWA performed adjacent to renal sinus but the Initial ablation success significantly differed between patients with RCCs ≤4cm (100%, 29/29) and RCCs >4cm (75%, 9/12, p=0.021). During the median follow-up of 37.6 (range, 3.0-97.3) months, the estimated 1-, 3-, and 5-year disease-free survival of patients with an initial tumor of ≤4cm were 100%, 89.7%, and 81.5%, respectively. The 1-, 3-, and 5-year RCCrelated survival were 100%, 93.3%, and 93.3%, respectively. The 1-, 3-, and 5-year overall survival were 97.1%, 87.8%, and 83.6%, respectively. There were no MWA-related deaths.

Tolerance and complications

Perioperative outcomes favor thermal ablation relative to surgical options. It has been proved that one of the main advantages of RFA compared to nephrectomy is the absence of any detectable renal function impairment after treatment even in solitary kidneys.

Compared to extirpative treatment options, RFA provide lowest rate of renal impairment [START_REF] Salas | Results of radiofrequency kidney tumor ablation: renal function preservation and oncologic efficacy[END_REF][START_REF] Pettus | Percutaneous radiofrequency ablation does not affect glomerular filtration rate[END_REF][START_REF] Cornelis | De novo renal tumors arising in kidney transplants: midterm outcome after percutaneous thermal ablation[END_REF]. Complications rate varies between 4 and 37% [START_REF] Atwell | Complications following 573 percutaneous renal radiofrequency and cryoablation procedures[END_REF] but for major complications, it is ranging from 0 to 8% [START_REF] Gervais | Radiofrequency ablation of renal cell carcinoma: part 2, Lessons learned with ablation of 100 tumors[END_REF][START_REF] Takaki | Radiofrequency ablation versus radical nephrectomy: clinical outcomes for stage T1b renal cell carcinoma[END_REF][START_REF] Hiraoka | Radiofrequency ablation for renal tumors: our experience[END_REF]. It is close to the results observed with open partial nephrectomy, which was 6.3% (4.5-8.7%) [START_REF] Hui | Comparison of percutaneous and surgical approaches to renal tumor ablation: metaanalysis of effectiveness and complication rates[END_REF]. Complications are mainly urinary fistulas (4.1%) and other urothelial lesions but also nerve injuries [START_REF] Gonzalez-Aguirre | Managing Complications Following Nephron-Sparing Procedures for Renal Masses[END_REF]. An increased risk in the case of central locations seems to be observed [START_REF] Balageas | Ten-year experience of percutaneous image-guided radiofrequency ablation of malignant renal tumours in high-risk patients[END_REF]. Some strategies have been developed to avoid this kind of complications. The risk of nerve injury may be minimized by mechanically separating the targeted tumor from vulnerable nerves using instillation of fluid or carbon dioxide. The risk of nerve injury may also be minimized by visualizing the ablation zone intraprocedurally, or monitoring the functional status of a motor or sensory pathway.

Retrograde renal cooling may help to protect the renal collecting system from injury during RFA without a decrease in expected lesion size.

Bleeding during cryoablation was associated with advanced age, increased tumor size, increased number of cryoprobes, and central position (P < .05). In the study of Atwell et al., major complication rates did not differ statistically (P = .15) between cryoablation (7.7%) and RF ablation (4.7%). Schmit et al. stratified [START_REF] Schmit | Predicting renal cryoablation complications: new risk score based on tumor size and location and patient history[END_REF] tumor and patient-related risk factors for major complications following renal cryoablation by developing the (MC)2 risk score for predicting these adverse events. After reviewing 398 renal ablation procedures, only maximal tumor diameter (P = .0006) and central tumor location (P = .02) were significantly associated with major complications. Among patient-related factors evaluated, prior myocardial infarction (MI) (P = .002) and complicated diabetes mellitus (P = .01) were significantly associated with major complications. Prophylactic superselective intra arterial tumor embolization before cryoablation for high risk patients with large tumors could be useful to decrease secondary bleeding and hematoma as well as limiting blood flow effect [START_REF] Moynagh | Percutaneous Cryoablation of Clinical T2 (> 7 cm) Renal Masses: Technical Considerations, Complications, and Short-Term Outcomes[END_REF].

Anaesthesia and perprocedural pain control

In most cases, percutaneous RF or MW ablation and cryoablation of renal lesions can be performed without general anesthesia and in an outpatient setting [START_REF] Su | Percutaneous computed tomography-guided radiofrequency ablation of renal masses in high surgical risk patients: preliminary results[END_REF]. For instance, paravertebral block associated with anesthesia of the kidney capsule may be an alternative to general anesthetic or conscious sedation in clinical practice [START_REF] Dubut | CT-guided paravertebral block for microwave ablation of kidney tumors: a new technique[END_REF]. But this consideration depends of several factors such as history or morphology of the patient. For technical reasons such as mobility of kidneys, general anesthesia is largely proposed in order to obtain apnea for patients and subsequently immobility of targeted lesions. Recently, some authors have proposed the high-frequency jet ventilation in tumor ablations techniques and showed promising preliminary results [START_REF] Denys | Use of High-Frequency Jet Ventilation for Percutaneous Tumor Ablation[END_REF]. This wide variability of practice renders the population quite heterogeneous and a selection bias can occur.

Few studies have compared the pain control requirements of patients undergoing percutaneous RFA with those of patients undergoing percutaneous cryoablation of small renal tumors. Allaf et al [START_REF] Allaf | Pain control requirements for percutaneous ablation of renal tumors: cryoablation versus radiofrequency ablation--initial observations[END_REF] compared outcome after conscious sedation of 10 men (mean age, 66.5 years) underwent cryoablation of 11 renal lesions, and 14 patients (11 men, four women; mean age, 68.1 years) underwent RFA of 15 renal tumors. Authors concluded that image-guided percutaneous cryoablation of small renal lesions appeared to require less analgesia than RFA. These results were confirmed by Truesdale et al in a study involving 71 patients who undergone RFA and 65 patients cryoablation [START_REF] Truesdale | Percutaneous computed tomography-guided renal mass radiofrequency ablation versus cryoablation: doses of sedation medication used[END_REF]. Prospective trials with validated pain scales are needed to examine this further for all ablative techniques.

Follow-up

As any other local therapy, patients may be seen regularly after treatment. The purpose of the first visit at 1-2 month is to detect complications. A follow-up contrast CT scan or MRI is thus performed. To detect recurrences, follow-up contrast CT scans or MRI are performed at 6, 12, 18 month and every year thereafter.

To assess the diagnosis of local recurrence, which corresponds to new nodular enhancement on cross-sectional imaging, examination with contrast injection must be performed. One reason is because some pitfall such as increased attenuation in low-density tissues such as perinephric fat can mask a lesion. Enhancement is considered significant when greater than 15HU on CT and 16% on MRI on the follow-up examinations [START_REF] Davenport | MRI and CT characteristics of successfully ablated renal masses: Imaging surveillance after radiofrequency ablation[END_REF]. For cryoablation a hypointense ring surrounding the ablative zone in T2 weighted sequence could be observed and seems to be useful for assess the recurrence.

Level of evidence and limitations

Extensive evidence is now available in the literature on the technical outcomes, the safety and the effectiveness of the use of percutaneous ablations for the treatment of T1a RCCs, with very good outcomes with respect to all three aspects. Based on long term studies, level of evidence is up to 2a thanks to systematic reviews (with homogeneity) of retrospective cohort studies.

It remains however challenging to compare outcomes between PN and these minimally invasive options as ablations are currently performed in an older population with many comorbid conditions compared to PN. Moreover, in many series, inconsistent reporting of definitive biopsy-proven RCC pathologic diagnosis avoid comparative analysis as well as the mix of percutaneous, laparoscopic, or open surgical ablative approaches. A direct randomized comparison of percutaneous ablation with PN in a large number of patients would be helpful to elucidate the role of both treatments. It would help to support a strong recommendation. However, such study looks highly challenging to perform as it would require multi-center registry with a large number of patients (>1000 at least) with biopsyproven sporadic T1a RCC followed up for a minimum of five years.

CONCLUSION:

In summary, percutaneous renal ablations are safe and effective in treating primary renal cell carcinomas. These mini-invasive therapeutic options contribute to the conservation of renal function and subsequently to the improvement of quality of life and life expectancy of patients even in cases of poor surgical candidates. However, as traditionally the dominant parameter for comparison of disease management strategies has been patient survival, longer-term survival data comparing available all treatment modalities may be needed though larger multi-institutional studies.

Figures

Figure 1: CT-guided renal radiofrequency ablation (RFA) of a 28mm right clear cell renal cell carcinoma in a 67 year-old man (RENAL score: 9a). A-Axial contrast enhanced CT-scan showed the T1a right renal tumor located anteriorly (arrowheads). B-A 35mm expendable radiofrequency antenna was inserted and deployed within the tumor (white arrow). C-A carbodissection of the perirenal space and renal sinus was performed by inserting a 22gauges needle (black arrow) and injecting CO2. This dissection was monitored during all the treatment to ensure sufficient organ displacement and avoid thermal injuries of the small bowel and the duodenum. D-The final control after RFA showed a tubulo-interstial edema (dashed arrow) surrounding the heterogeneous ablation zone. A-Axial contrast enhanced CT-scan showed the left T1a renal tumor (arrowheads). B-A microwave antenna was inserted in the tumor (white arrow) and a carbodissection of the perirenal space was performed. C-Gas formation within the tumor and slight shrinkage of the tumor were observed during treatment (black arrow). D-The final control after MWA showed dense charred tissue (dashed arrow) in the ablation zone.

Figure 2 :

 2 Figure 2: CT-guided renal cryoablation of a 35mm right clear cell renal cell carcinoma in a 72 year-old man (RENAL score: 9a). A-Axial contrast enhanced CT-scan showed the T1a right renal tumor (arrow). B-Two cryoprobes were inserted within the tumor. C-A carbodissection was performed by injecting CO2 trough a 22G needle to ensure protection of abdominal wall and liver capsule (dashed arrow). D-The iceball covered the whole tumor at the end of the second freeze (arrowheads).

Figure 3 :

 3 Figure 3: CT guided renal microwave ablation of a 28mm left clear cell renal cell carcinoma in a 69 year-old man (RENAL score: 9x).A-Axial contrast enhanced CT-scan showed the left T1a renal tumor (arrowheads). B-A microwave antenna was inserted in the tumor (white arrow) and a carbodissection of the perirenal space was performed. C-Gas formation within the tumor and slight shrinkage of the tumor were observed during treatment (black arrow). D-The final control after MWA showed dense charred tissue (dashed arrow) in the ablation zone.

Conflict of interests: None


Jérôme Brunelin

Marine Mondino
email: marine.mondino@ch-le-vinatier.fr

Clément Dondé

Layla Lavallé

Frédéric Haesebaert

Reality-monitoring deficits and visual hallucinations in schizophrenia

Keywords: Schizophrenia and psychosis, hallucinations, source memory, source-monitoring, selfrecognition

Introduction

Hallucinations are classically defined as perception-like experiences that occur without an external stimulus, in an awake state, with the physical properties and the sense of reality of real perceptions, and that are not under voluntary control [START_REF] Aleman | On Redefining Hallucination[END_REF][START_REF] Slade | Sensory deception: A scientific analysis of hallucination[END_REF]. Hallucinations may involve all sensory modalities but, in patients with schizophrenia, their prevalence differs according to the sensory modality involved. Specifically, their lifetime prevalence is estimated at 64-80% for auditory, 23-31% for visual, 9-19% for tactile, and 6-10% for olfactory hallucinations [START_REF] Mccarthy-Jones | Occurrence and co-occurrence of hallucinations by modality in schizophrenia-spectrum disorders[END_REF]. Given their predominance, hallucinations in the auditory modality (AH) are considered a hallmark of schizophrenia and have been the focus of most studies in the field. By contrast, relatively little consideration has been given to the co-occurrence of hallucinations in other modalities. Recently, McCarthy-Jones et al. reported that 30-37% of patients with lifetime AH had also experienced visual hallucinations (VH), and that, in reverse, 83-97% of patients with experience of VH had also experienced AH [START_REF] Mccarthy-Jones | Occurrence and co-occurrence of hallucinations by modality in schizophrenia-spectrum disorders[END_REF]. This co-occurrence suggests common hallucinatory mechanisms in addition to specific modality-dependent dysfunctions [START_REF] Waters | Visual Hallucinations in the Psychosis Spectrum and Comparative Information From Neurodegenerative Disorders and Eye Disease[END_REF].

Critically, the presence of VH in addition to AH (V+AH) is associated with a more severe psychopathological profile and a less favorable prognosis [START_REF] Clark | On the interconnectedness and prognostic value of visual and auditory hallucinations in first-episode psychosis[END_REF]. Due to their impact on functioning, there is a crucial need to increase knowledge about these symptoms and particularly their underlying cognitive mechanisms.

During the last decades, some cognitive models have been proposed to explain positive symptoms such as hallucinations [START_REF] Waters | Auditory Hallucinations in Schizophrenia and Nonschizophrenia Populations: A Review and Integrated Model of Cognitive Mechanisms[END_REF]. One of them assumes that hallucinations arise from a failure of reality-monitoring processes, specifically resulting in misattribution of internally generated events, such as thoughts or mental images, as being perceived from an external source [START_REF] Bentall | Reality monitoring and psychotic hallucinations[END_REF][START_REF] Morrison | Intrusive Thoughts and Auditory Hallucinations: A Cognitive Approach[END_REF][START_REF] Morrison | Cognitive factors in predisposition to auditory and visual hallucinations[END_REF]. This type of misattribution, also called an externalization bias, may result from mental imagery having more perceptual characteristics than expected or from reduced cognitive operations associated with imagined information making the memory unlikely to have been internally-generated [START_REF] Johnson | Reality monitoring[END_REF][START_REF] Johnson | Source monitoring[END_REF]. Several studies and meta-analyses have supported this model by showing that patients with hallucinations have a greater tendency to misattribute internal items to external sources than patients without hallucinations and healthy individuals [START_REF] Brookwell | Externalizing biases and hallucinations in source-monitoring, self-monitoring and signal detection studies: a meta-analytic review[END_REF][START_REF] Brunelin | Source monitoring deficits in hallucinating compared to non-hallucinating patients with schizophrenia[END_REF]. Even if early reality-monitoring models of hallucinations [START_REF] Bentall | Reality monitoring and psychotic hallucinations[END_REF] did not propose that the deficits would concern some specific sensory modalities of hallucinations rather than others, most of the studies focused on AH. For instance, we reported that patients with AH misattributed more words they had imagined as being actually heard compared to patients without AH [START_REF] Brunelin | Source monitoring deficits in hallucinating compared to non-hallucinating patients with schizophrenia[END_REF]. To the best of our knowledge, only few studies investigated realitymonitoring deficits in relationship with hallucinations in the visual modality in patients with schizophrenia. They showed that patients with VH misremembered items that had been presented as words as having been presented as pictures [START_REF] Aynsworth | Reality monitoring performance and the role of visual imagery in visual hallucinations[END_REF][START_REF] Brébion | Visual hallucinations in schizophrenia: confusion between imagination and perception[END_REF][START_REF] Siddi | Remembering verbally-presented items as pictures: Brain activity underlying visual mental images in schizophrenia patients with visual hallucinations[END_REF]. These results suggest that a failure in reality-monitoring processes may constitute a good candidate for the mechanism underlying hallucinatory phenomenon. However, little is known about the impact of presenting hallucinations in both visual and auditory modalities on reality-monitoring peformance.

In this context, the aim of the present study was to test whether reality-monitoring deficits are associated with V+AH in schizophrenia. To this end, we investigated realitymonitoring performances in two groups of schizophrenia patients with hallucinations: a group with only AH (i.e., patients that never reported VH) and a group with V+AH, as done in studies exploring VH in schizophrenia [START_REF] Amad | The multimodal connectivity of the hippocampal complex in auditory and visual hallucinations[END_REF][START_REF] Cachia | Deviations in cortex sulcation associated with visual hallucinations in schizophrenia[END_REF][START_REF] Rolland | Resting-State Functional Connectivity of the Nucleus Accumbens in Auditory and Visual Hallucinations in Schizophrenia[END_REF]. We hypothesized that patients with V+AH would display more severe reality-monitoring deficits than patients with AH only. More precisely, we proposed that experiencing hallucinations in several sensory modalities would increase the perceptual characteristics associated with imagined events and lead to a more severe externalization bias.

Materials and methods

Participants

Fifty patients with schizophrenia were included in the study. All participants met the DSM-IV-TR criteria for schizophrenia based on a clinical interview with an experienced psychiatrist using the Mini-International Neuropsychiatric Interview (M.I.N.I) [START_REF] Sheehan | The Mini-International Neuropsychiatric Interview (M.I.N.I.): the development and validation of a structured diagnostic psychiatric interview for DSM-IV and ICD-10[END_REF]. All participants were native French-speakers and displayed refractory treatment-resistant AH, defined as the persistence of daily AH despite antipsychotic treatment at an adequate dosage for at least 6 weeks. The Positive and Negative Syndrome Scale (PANSS) was used to evaluate the general symptomatology [START_REF] Kay | The positive and negative syndrome scale (PANSS) for schizophrenia[END_REF] and the Auditory Hallucination Rating Scale (AHRS, range 0-42) was used to provide a specific and extensive measure of AH severity [START_REF] Hoffman | Transcranial Magnetic Stimulation of Left Temporoparietal Cortex and Medication-Resistant Auditory Hallucinations[END_REF]. Participants were carefully divided into two groups based on the presence of VH measured by the item #6 of the Scale for the Assessment of Positive Symptoms (SAPS [START_REF] Andreasen | The Scale for the Assessment of Positive Symptoms (SAPS)[END_REF]): a group of patients with AH and no VH (AH group, n = 24, SAPS-item #6 = 0) and a group of patients with AH and VH (V+AH group, n = 22, SAPS-item #6 ≥ 2, i.e., VH ranging from "2mild" to "5-severe" intensity). SAPS-item #6 assess VH by asking if "the patient sees shapes or people that are not actually present". Participants with questionable VH (SAPS-item #6 = 1) were excluded (n = 4). Participants characteristics are detailed in Table 1.

All patients gave their written informed consent. All experiments were approved by a local ethics committee and performed in accordance with relevant guidelines and regulations. ** please insert Table 1 about here **

Reality-monitoring task

Reality-monitoring performances were assessed using a previously described task that measures confusion between imagined words and heard words ('Hear-Imagine' task) [START_REF] Brunelin | Source monitoring deficits in hallucinating compared to non-hallucinating patients with schizophrenia[END_REF][START_REF] Brunelin | Impaired verbal source monitoring in schizophrenia: An intermediate trait vulnerability marker?[END_REF].

All participants completed a short practice trial to become acquainted with the task requirements and to ensure the understanding and the good realization of instructions. The task was separated into two phases: an encoding phase and a memory retrieval phase. During the encoding phase, 16 words were presented one by one in a randomized order in the centre of a computer screen for 3s. Each word was immediately preceded by its respective instruction, either "Imagine yourself hearing the following word" or "Listen to the following word". Half of the words (8 words) had to be heard and their visual presentation was accompanied by an auditory stimulus (i.e., the experimenter voice speaking the word once).

The other half (8 words) had to be imagined by the participant and no auditory stimulus was presented. The memory retrieval phase began immediately after the end of the encoding phase. During this phase, participants were presented with a response grid including the 16 words previously presented during the encoding phase, plus 8 new words which had not previously been presented. For each word, participants were asked to answer whether the word was heard, imagined or if the word was not presented during the encoding phase.

Two main outcomes were measured: 1) the externalization bias, measured as the number of imagined words that were classified as heard (range 0-8), and 2) the internalization bias, measured as the number of heard words that were classified as imagined (range 0-8) [START_REF] Brunelin | Source monitoring deficits in hallucinating compared to non-hallucinating patients with schizophrenia[END_REF].

Statistical analyses

Data were analyzed with JASP (Version 0.9; JASP Team, 2018). Between group comparisons were computed using two-sample t-tests for continuous outcomes and Chi-square tests for categorical data. For misattribution biases comparisons, Cohen's d effect sizes were also computed. All tests were two-tailed and statistical significance was set at p < 0.05. In case of a significant effect, the potential confounding role of gender was assessed using a two-way ANOVA with Group and Gender as between-group factors.

Results

Demographic and clinical characteristics

No significant differences were reported between AH and V+AH groups for age, education, illness duration, AH severity measured by the AHRS and general symptomatology severity assessed by the total PANSS score (all p > 0.05, see Table 1). However, the two groups differed significantly on gender (χ 2 = 8.626, p = 0.003).

Reality monitoring performance

Patients with V+AH displayed a significantly higher externalization bias as compared to patients with AH (t(44) = -2.78, p = 0.008, d = -0.82; see Figure 1). In other words, patients with V+AH misrecognized more imagined words as being heard (M = 2.18, SD = 1.71) than patients with AH only (M = 1.00, SD = 1.14). No difference was found between groups for the internalization bias, i.e. the misrecognition of heard words as being imagined (t(44) = 1.04, p = 0.31, d = 0.31). ** please insert Figure 1 about here ** In order to rule out the potential confounding role of gender in our analyses, we examined the effect of gender on the externalization bias with a two-way ANOVA with Group and Gender as between-group factors. We found no significant effects of Gender (F(1, 42) = 0.31, p = 0.58) and Group*Gender interaction (F (1, 42) = 1.75, p = 0.20). By contrast, the effect of Group remained significant (F(1, 42) = 4.70, p = 0.036).

Discussion

The present study proposed an original investigation of reality-monitoring performance in patients with schizophrenia who present with V+AH. Findings indicated that patients with V+AH displayed a higher externalization bias than patients with AH, which means that patients with V+AH were more likely to remember imagined words as being perceived compared to patients with AH only.

The existence of a misattribution bias in patients with VH has already been described in the literature in schizophrenia [START_REF] Aynsworth | Reality monitoring performance and the role of visual imagery in visual hallucinations[END_REF][START_REF] Brébion | Visual hallucinations in schizophrenia: confusion between imagination and perception[END_REF][START_REF] Siddi | Remembering verbally-presented items as pictures: Brain activity underlying visual mental images in schizophrenia patients with visual hallucinations[END_REF][START_REF] Brébion | Source memory errors in schizophrenia, hallucinations and negative symptoms: a synthesis of research findings[END_REF]. For instance, [START_REF] Brébion | Visual hallucinations in schizophrenia: confusion between imagination and perception[END_REF] found that patients with VH were more likely to report that they had seen pictures of items when only the verbal label of these items had been displayed. However, in these studies, reality-monitoring was tested using stimuli in the visual modality only (i.e. words and pictures), making it difficult to decipher whether the externalization bias was modality-specific or not. By contrast, Arguedas et al.' s investigated the modality-specificity of reality-monitoring impairments [START_REF] Arguedas | Source monitoring and olfactory hallucinations in schizophrenia[END_REF]. Authors found that patients with olfactory hallucinations were less accurate in distinguishing between imagined and smelled odors than patients with AH and healthy controls and, additionally, that patients with AH were less accurate in distinguishing the source of a spoken word. However, the verbal reality-monitoring task used in Arguedas et al.' s design did not involve a distinction between imagined and perceived events, as done in our study, but a distinction between self-produced words and words produced by the experimenter. It is likely that such distinction is not related to the same cognitive mechanisms as those involved in discriminating imagination from perception.

In our study, we tested reality-monitoring performances in the auditory modality and demonstrated that V+AH patients were more likely to misattribute imagined words as being heard than patients with AH only. Given that the two groups did not differ in AH and other symptoms severity, we propose that the misattributions observed may not be specific of the sensory modality but rather reflect an amodal deficit in discriminating imagination from reality. This interpretation is consistent with Garrison et al.' study, which reported that even if reality-monitoring accuracy was better for imagined stimuli in the visual than in the auditory modality, the level of externalization bias was independent of the modality of presentation of the stimuli [START_REF] Garrison | Monitoring what is real: The effects of modality and action on accuracy and type of reality monitoring error[END_REF]. To confirm that the modality used to measure reality-monitoring did not influence the observed externalization bias, it would be of great interest to include a visual reality-monitoring task, together with the present auditory task, in a further study.

One can hypothesize that patients with V+AH display a more severe misattribution bias because of increased perceptual details associated to the imagined event that may lead to greater confusion when identifying the source of this event. This is consistent with the hypothesis of increased vividness of mental images associated with VH, which has been supported by evidence of a relationship between proneness to VH and vivid imagery in nonclinical people with VH [START_REF] Aynsworth | Reality monitoring performance and the role of visual imagery in visual hallucinations[END_REF]. In addition, the hypothesis of increased perceptual details associated to the imagined event is consistent with the abnormal overactivity of sensory cortice observed during hallucinations such as the hyperactivation of superior temporal regions for AH and visual cortices for VH [START_REF] Zmigrod | The neural mechanisms of hallucinations: A quantitative meta-analysis of neuroimaging studies[END_REF], which might produce more vivid perceptual content than usually associated with imagined events. Alternative explanations for the increased externalization bias independently of the vividness of mental images would be that patients with V+AH associate less cognitive operations information to imagined events [START_REF] Johnson | Memory and reality[END_REF] or display greater deficits in the ability to compare imagined and real events [START_REF] Bentall | Reality testing and auditory hallucinations: A signal detection analysis[END_REF].

Besides, the findings of a misattribution bias in patients with VH is consistent with a previous study showing a greater propensity to report imagined stimuli as percepts in patients with Parkinson disease and VH [START_REF] Barnes | Reality monitoring and visual hallucinations in Parkinson's disease[END_REF]. Since a similar misattribution bias was reported in nonclinical people with high predisposition to VH, one could hypothesize that the realitymonitoring deficit constitutes a common mechanism that underlies VH regardless of the diagnostic category.

Despite the original findings, several limits should be acknowledged. First, one can hypothesize that the observed difference between groups is supported by the difference in gender proportion between our samples. Since our analyses revealed no effect of gender on the externalization bias, the between-group difference in terms of gender is unlikely to account for the present observation of an increased externalization bias in patients with V+AH. The observed gender imbalance between V+AH and AH patients is in line with some previous studies reporting a higher risk for VH in females than in males [START_REF] Thomas | Correlates of hallucinations in schizophrenia: A cross-cultural evaluation[END_REF]. However, a more recent study investigating the prevalence and co-occurrence of hallucinations across the auditory, visual, olfactory, and tactile modalities, in two large samples of people diagnosed with chronic schizophrenia-spectrum disorders found no consistent association between VH (or any modality of hallucination) and gender [START_REF] Mccarthy-Jones | Occurrence and co-occurrence of hallucinations by modality in schizophrenia-spectrum disorders[END_REF]. Second, we cannot exclude that the more severe reality-monitoring deficits observed in the V+AH group could be due to more severe general cognitive deficits in V+AH. In the current sample, we compared PANSS cognitive dimension scores [START_REF] Lindenmayer | A new five factor model of schizophrenia[END_REF] between groups and observed no differences between V+AH (mean= 11.73, SD= 3.24) and AH groups (mean= 11.77, SD= 3.28; p=0.96). However, further studies with standardized cognitive evaluations are required to address this issue. In addition, the greater deficits observed in the V+AH group could be linked to greater visual processing deficits. Indeed, studies in patients with Parkinson disease have reported a relationship between VH and altered visual processing [START_REF] Diederich | Hallucinations in Parkinson disease[END_REF][START_REF] Bernardin | Retinal ganglion cells dysfunctions in schizophrenia patients with or without visual hallucinations[END_REF] and there is also evidence that patients with Parkinson disease and VH showed deficits in both visual perception and source monitoring [START_REF] Barnes | Reality monitoring and visual hallucinations in Parkinson's disease[END_REF]. To decipher on the contribution of visual abnormalities to the reality-monitoring deficits in patients with schizophrenia, studies investigating visual processing together with realitymonitoring are needed. Third, one potential limitation of the present study is that no healthy individuals were compared to the patient groups. However, regarding repeated evidence of reality-monitoring impairment in schizophrenia (reviewed in [START_REF] Brookwell | Externalizing biases and hallucinations in source-monitoring, self-monitoring and signal detection studies: a meta-analytic review[END_REF]), we can reasonably assume that our samples of participants display reality-monitoring deficits. Furthermore, the study was designed to assess the effects that were specific to the sensory modality involved in hallucinations, i.e., AH or V+AH, rather than the effects that were more broadly related to schizophrenia and medication. Fourth, although the task used to measure reality-monitoring processes in our study was similar to the paradigms that have been previously used to assess reality-monitoring, with imagined and heard words presented visually [START_REF] Brunelin | Source monitoring deficits in hallucinating compared to non-hallucinating patients with schizophrenia[END_REF][START_REF] Keefe | Source monitoring deficits in patients with schizophrenia; a multinomial modelling analysis[END_REF][START_REF] Sugimori | Brain Mechanisms Underlying Reality Monitoring for Heard and Imagined Words[END_REF][START_REF] Moseley | Investigating the roles of medial prefrontal and superior temporal cortex in source monitoring[END_REF], this task came with some limitations. Indeed, we cannot exclude that participants may not have always followed the instruction to imagine hearing the visually presented words and that it could have affected their performance during the retrieval phase. Finally, the tools used to assess hallucinations in our sample of schizophrenia patients did not allow us to differenciate multimodal hallucinations in different sensory domains at the same time, as well as serial multimodal hallucinations that occurred at separate times. Since simultaneous multimodal hallucinations are associated with a greater sense of reality and distress [START_REF] Dudley | Prevalence and characteristics of multi-modal hallucinations in people with psychosis who experience visual hallucinations[END_REF], it would have been relevant to explore whether they were associated to a higher externalization bias.

In summary, we present evidence that patients with schizophrenia who have V+AH display a higher deficit in reality-monitoring abilities than patients with schizophrenia who only have AH. Experiencing hallucinations in two sensory modalities is associated with a greater tendancy to misattribute imagined events as being actually perceived from an external source. A better understanding of the cognitive processes underlying the presence of V+AH in patients with schizophrenia could help identify some potential targets for clinical interventions. These findings support the interest of developping psychological interventions that aim to overcome reality-monitoring deficits in patients with V+AH, as done by two previous studies reporting promising results [START_REF] Favrod | A first step toward cognitive remediation of voices: a case study[END_REF][START_REF] Subramaniam | Computerized cognitive training restores neural activity within the reality monitoring network in schizophrenia[END_REF]. measured as the number of imagined words that were classified as heard (range 0-8) and the internalization bias is measured as the number of heard words that were classified as imagined (range 0-8). [START_REF] Brunelin | Source monitoring deficits in hallucinating compared to non-hallucinating patients with schizophrenia[END_REF] Results are displayed as mean +/-standard error. ns = not significant.

Figure 1 .

 1 Figure 1. Comparison of reality-monitoring performance between patients with V+AH

Table 1 .

 1 Demographic and clinical characteristics of patients with AH and patients withAll values are mean (SD). Groups were compared using two-sample t-tests, except for gender where a Chi-square test was used. * significant difference between groups (p < 0.05)

	V+AH.
		AH Group	V+AH Group
				P value
		(N= 24)	(N= 22)
	Gender (Male/Female)	18 / 6	7 / 15	0.003*
	Age (years)	36.2 (9.3)	36.4 (10.2)	0.96
	Education (years)	11.3 (2.5)	12.5 (2.6)	0.11
	Illness duration (years) 10.6 (8.2)	9.8 (7.0)	0.73
	PANSS total score	73.2 (15.5)	73.4 (17.9)	0.96
	AHRS score	25.5 (6.4)	27.1 (6.2)	0.42
	SAPS-item #6	0 (0)	2.9 (0.9)	-


MD Thomas Similowski

MD Valery Trosini-Désert
email: valery.trosini-desert@aphp.fr

MD Florence Jeny

MD Philippe Maksud

PhD Alain Giron

MD PhD Vincent Degos

Contribution of endobronchial ultrasound elastography to

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

HIGHLIGHTS

• EBUS elastographic parameters differ in malignant compared to benign nodes. (77 characters)

• EBUS elastography can contribute to the prediction of the nature of lymph nodes. (82 characters)

• Elastography can provide reliable complementary information when combined with EBUS. (86 characters) KEYWORDS (max 4): diagnosis, mediastinal lymphadenopathy, elastrography, endobronchial ultrasound transbronchial needle aspiration ABBREVIATIONS: AUC, area under the curve; CART, classification and regression tree; CT, computed tomography; EBUS, endobronchial ultrasound; EUS, endoscopic ultrasound; FNA, fine-needle aspiration; IQR, interquartile range; NPV, negative predictive value; NSCLC, non-small cell lung cancer; PET, positron emission tomography; PPV, positive predictive value; ROC, receiver operating characteristic; SUV, standardized uptake value; TBNA, transbronchial needle aspiration

INTRODUCTION

Mediastinal lymph nodes are commonly demonstrated on Computed Tomography (CT) chest scan in the context of staging of known or suspected malignant lung cancer or hematological malignancies (25% of non-small cell lung cancers [NSCLCs] are associated with mediastinal lymphadenopathy at the time of diagnosis) [START_REF] Gu | Endobronchial ultrasoundguided transbronchial needle aspiration for staging of lung cancer: a systematic review and meta-analysis[END_REF]. Alternatively, this can be increasingly an incidental finding on CT scans performed in settings other than thoracic oncology.

Characterization of the benign or malignant nature of mediastinal lymphadenopathy therefore constitutes a major clinical challenge.

The reference technique to characterize mediastinal lymphadenopathy is surgical exploration of the mediastinum (mediastinoscopy). Less invasive endoscopic techniques can also be used to determine the benign or malignant nature of mediastinal lymph nodes. Endobronchial ultrasound (EBUS) with transbronchial needle aspiration (TBNA) has a sensitivity of 93% and a specificity of 100% to identify malignant lymphadenopathy [START_REF] Gu | Endobronchial ultrasoundguided transbronchial needle aspiration for staging of lung cancer: a systematic review and meta-analysis[END_REF]. Endoscopic ultrasound (EUS) with fine-needle aspiration (FNA) has a sensitivity of 81-97% and a specificity of 83-100% [START_REF] Vazquez-Sequeiros | Diagnostic yield and safety of endoscopic ultrasound guided fine needle aspiration of central mediastinal lung masses[END_REF]. Although these operating values are good, it is nevertheless legitimate to try to improve these performances while avoiding a more invasive approach. Preliminary data suggest that EBUS combined with elastography could improve the diagnostic yield of EBUS-TBNA [START_REF] Trosini-Desert | Bronchial endoscopic ultrasound elastography: preliminary feasibility data[END_REF].

The first elastography studies were combined with the use of ultrasound, leading to the development of ultrasound elastography. This technique can be performed using two approaches, depending on whether the applied constraint is almost static (e.g. by compression of the medium with the probe) or dynamic (generation and propagation of shearing waves in the medium studied). Static elastography consists of characterization of the mechanical properties of a tissue or a tissue zone in terms of its response to the application of a mechanical constraint. As 'soft' zones are more easily deformed than 'hard' zones, comparison of images of the region of interest before and after application of the constraint allows identification of the most suspicious zones (4). The ultrasound waves reflected by tissues are analyzed and restored in the form of a color map superimposed on the conventional endobronchial ultrasound image (integration of an elastographic module in the standard ultrasound equipment) [START_REF] Ophir | Elastography: a quantitative method for imaging the elasticity of biological tissues[END_REF]. Static elastography has mainly been developed in combination with surface ultrasound imaging (5-10), but has also been described in combination with gastrointestinal endoscopic ultrasound [START_REF] Giovannini | Endoscopic ultrasound elastography for evaluation of lymph nodes and pancreatic masses: a multicenter study[END_REF][START_REF] Saftoiu | State-of-the-art imaging techniques in endoscopic ultrasound[END_REF][START_REF] Sakamoto | Endosonographic detection of mediastinal lymph node metastasis in superficial carcinoma of the esophagus: assessment by type classification and histogram[END_REF].

This large-scale study was performed to evaluate elastography combined with EBUS-TBNA and the relationship between elastographic characteristics and the cytological and histological diagnosis obtained by transbronchial needle aspiration or mediastinoscopy.

MATERIALS AND METHODS

Study design

This single-center, prospective, observational study was conducted in the bronchial endoscopy unit of the Department of Respiratory Medicine and Intensive Care at the Pitié-Salpêtrière Hospital, Paris, France. The Comité de Protection des Personnes Ile-de-France VI Pitié-Salpêtrière (Independent Ethics Committee/Institutional Review Board) reviewed and approved the study protocol. The elastographic examination was integrated into a clinical diagnostic procedure and so did not require any modification of the clinical examination.

Patients were informed about the elastographic measurements and provided their consent to participate before the examination. The only inclusion criterion was the presence of an indication for endobronchial ultrasound for exploration of mediastinal lymphadenopathy.

Exclusion criteria consisted of a history of mediastinal radiotherapy or thoracic surgery, as well as any general contraindications to endobronchial ultrasound [START_REF] Douadi | Endobronchial ultrasound (EBUS): the state of the art[END_REF]. Minors or adults not able to provide informed consent were not included in the study. Examinations were performed under general anesthesia, according to the unit's current procedures, between February 2012 and June 2014.

Elastography procedure

Real-time elastographic mapping was performed using an ultrasound elastography module incorporated in an ultrasound machine (Hi-vision Avius ® , Hitachi Medical Systems, Kashiwa, Japan, CE-0197) combined with an endobronchial ultrasound probe (EB1970 videobronchoscope, Pentax, Tokyo, Japan, CE-0123).

The real-time tissue elastography module of the Hitachi (HI-RTE) ultrasound machine used an Extended Combined Autocorrelation Method to produce real-time elasticity images. Four parameters were studied: 1) color score (qualitative data), corresponding to color coding of relative tissue elasticity superimposed onto the B-mode image (11) (Figure 1); 2) average tissue elasticity (qualitative data), corresponding to color averaging of 2-4 compression/decompression cycles; 3) strain ratio (quantitative data), corresponding to the elasticity ratio calculated between the lymph node studied and an apparently healthy surrounding zone (15); 4) percentage of hard areas (histogram) (quantitative data), corresponding to the colorimetric distribution within a selected zone of the lymph node [START_REF] Sakamoto | Endosonographic detection of mediastinal lymph node metastasis in superficial carcinoma of the esophagus: assessment by type classification and histogram[END_REF].

Transbronchial needle aspiration was performed using a 22 gauge needle (Sono Tip ® EBUS, MediGlobe, Germany, CE-0483) by targeting the zone identified as being the least elastic.

Final diagnosis

At least three TBNA samples were taken from each lymph node studied [START_REF] Lee | Real-time endobronchial ultrasound-guided transbronchial needle aspiration in mediastinal staging of non-small cell lung cancer: how many aspirations per target lymph node station?[END_REF]. The presence of tumor cells on histological examination was considered to be sufficient proof of the malignant nature of the node. An unambiguous diagnosis of tuberculosis or sarcoidosis was accepted as sufficient proof of the benign nature of the node. In the absence of such results (normal node structure or inadequate material), the decision to perform mediastinoscopy or surveillance was taken as a function of the degree of clinical suspicion of malignancy, evaluated at a multidisciplinary consultation meeting according to Good Clinical Practice guidelines. For mediastinoscopy, the procedure was performed within a period of 2 weeks after the decision.

For surveillance, a chest CT scan was performed at 3 months and 6 months combined with Positron Emission Tomography (PET) scan. Mediastinoscopy was systematically performed when progression was observed during follow-up. In the absence of any morphological and metabolic changes at 6 months, the lymphadenopathy was considered to be benign. Of note, PET scan was not performed in all patients (maximum standardized uptake value [SUVmax] was available for only 69 nodes).

Statistical analysis

Statistical analyses were performed with JMP ® software (SAS institute). Continuous variables were described as mean±SD or median±interquartile range (IQR) and categorical variables were described as number (percentage). Data were compared using Student's t-test or

Wilcoxon signed rank test depending on the distribution. Categorical data were compared using a Chi-square test. One-way analysis of variance with post hoc protected Tukey-Kramer test was performed to compare multiple means (or Kruskal-Wallis nonparametric analysis of variance, depending on the distribution). Correlations between variables were studied using Pearson's correlation coefficient or Spearman's correlation coefficient, depending on the distribution. Stepwise multivariate logistic linear regression was used to identify predictors of tumor status. Receiver operating characteristic (ROC) curves were generated and the corresponding areas under the curves (AUC) were calculated. Segmentation was performed i) by choosing a trade-off between sensitivity and specificity using the optimal Youden index defined as: (sensitivity)+(specificity)-1 and ii) to fit with the clinical strategy by selecting as cut-off the first value associated with a negative predictive value (NPV)=1. Finally, a classification and regression tree (CART) procedure was used to predict tumor status. Twosided p-values <0.05 were considered significant. (p=0.003). Additionally, malignant nodes had a significantly higher elasticity ratio, percentage of hard areas and colorimetric score, and a significantly lower average elasticity than benign nodes (p<0.001). The ROC curves of the various elastographic parameters were not significantly different (Figure 2), although AUC was highest for the colorimetric score ROC curve.

RESULTS

Patients and lymph nodes assessed

A
Sensitivity, specificity, positive predictive value (PPV) and NPV at the Youden cutoff (equal sensitivity and specificity cut-off), estimated from the prevalence of 40% of malignant lymph nodes in our population (Table 3), were 0.77, 0.89, 0.83 and 0.86 for average elasticity; 0.86, 0.73, 0.71, 0.87 for strain ratio; 0.73, 0.92, 0.86, 0.84 for percentage of hard areas; and 0.77, 0.95, 0.92, 0.86 for colorimetric score. These predictive performances of elastographic parameters were higher than those observed for SUVmax (Table 3).

In clinical practice, it is important not to miss a malignant lesion to avoid a loss of chance for the patient and to avoid iatrogenic effects related to unnecessary surgery on benign lesions.

This trade-off can be achieved by setting the NPV of elastographic parameters to 100%. In this way, all lymph nodes demonstrated to be 'soft' on elastography can be reliably considered to be benign, avoiding systematic follow-up mediastinoscopy after negative aspiration (TBNA) for certain patients, with no risk of allowing the progression of a malignant lesion. Setting the NPV to 100% modifies the limits of detection of the various parameters (84.8 for average elasticity; 1.4 for the strain ratio; 32.6 for the percentage of hard areas and 3 for the colorimetric score), resulting in a lower specificity of the test (Table 4), but which can be corrected by including the performances of various multivariate models, such as a simple model comprising colorimetric data and node diameter, which appears to constitute a useful compromise (Table 4).

The Classification and Regression Tree (CART) approach identifies three homogeneous groups with no overlap: colorimetric score 1 or 2 -lymph node considered to be benign; colorimetric score 3 and diameter <13.8 mm -lymph node considered to be benign; colorimetric score 4 and average elasticity <54 -lymph node considered to be malignant.

For lymph nodes classified by one of these three rules, EBUS-TBNA is associated with a sensitivity and specificity of 100%. Lymph nodes not classified by these rules (n=42 [39%]),

i.e. those with a colorimetric score of 3 and diameter >13.8 mm or those with a colorimetric score of 4 and average elasticity >54, correspond to 50% benign nodes and 50% malignant nodes.

A more detailed analysis of elastographic criteria also showed a globally significant difference between histological types (Table 5). Although malignant nodes can be significantly distinguished from benign nodes, no significant difference in terms of elastographic criteria was observed between the malignant histological subtypes, or between the benign histological subtypes.

DISCUSSION

This study suggests that the diagnostic yield of EBUS-TBNA could be improved by combining EBUS-TBNA with elastography, as already demonstrated for gastrointestinal endoscopic ultrasound. In general, and as expected, the results of this study show that benign nodes have a softer appearance in terms of elastographic variables, while malignant nodes are harder. More precisely, a colorimetric score <3, a strain ratio <1.4, an average elasticity >84.8, and a percentage of hard zones <32 have an NPV of 100% for malignancy. When none of these values is observed, a negative TBNA (not showing any malignant cells) remains inconclusive and further investigations and/or surveillance are required.

Comparison with the literature

Only a few studies have been published on the use of elastography in respiratory medicine [START_REF] García | Initial experience with real-time elastography using an ultrasound bronchoscope for the evaluation of mediastinal lymph nodes[END_REF][START_REF] He | Endobronchial ultrasound elastography for diagnosing mediastinal and hilar lymph nodes[END_REF][START_REF] Inage | Endobronchial elastography in the evaluation of esophageal invasion[END_REF][START_REF] Izumo | Endobronchial ultrasound elastography in the diagnosis of mediastinal and hilar lymph nodes[END_REF][START_REF] Sivokozov | The first experience in using elastography in combination with endobronchial ultrasonography for mediastinal pathology: Preliminary assessment of feasibility and comparison of characteristics via different approaches[END_REF][START_REF] Fournier | Performance of endobronchial ultrasound elastography in the differentiation of malignant and benign mediastinal lymph nodes: results in real-life practice[END_REF][START_REF] He | Value of endobronchial ultrasound elastography in the diagnosis of mediastinal and hilar lymph node metastasis in lung cancer[END_REF][START_REF] Huang | Effectiveness of the benign and malignant diagnosis of mediastinal and hilar lymph nodes by endobronchial ultrasound elastography[END_REF][START_REF] Nakajima | Elastography for predicting and localizing nodal metastases during endobronchial ultrasound[END_REF][START_REF] Rozman | Endobronchial ultrasound elastography strain ratio for mediastinal lymph node diagnosis[END_REF][START_REF] Dietrich | Endobronchial ultrasound elastography[END_REF] and, to the best of our knowledge, no study other that our own preliminary study [START_REF] Trosini-Desert | Bronchial endoscopic ultrasound elastography: preliminary feasibility data[END_REF] has analyzed all four elastographic variables. The available data support those described in the present study. In an assessment of lymph nodes by elastography with EBUS using colorimetric analysis, sensitivity, specificity, PPV, and NPV were 100%, 92.3%, 96.7%, and 100%, respectively [START_REF] Izumo | Endobronchial ultrasound elastography in the diagnosis of mediastinal and hilar lymph nodes[END_REF]. Other studies have shown the strain ratio to be more reliable than color mapping and conventional B-mode EBUS to predict the benign or malignant nature of lymph nodes [START_REF] He | Endobronchial ultrasound elastography for diagnosing mediastinal and hilar lymph nodes[END_REF][START_REF] Rozman | Endobronchial ultrasound elastography strain ratio for mediastinal lymph node diagnosis[END_REF], and the elastographic score has been shown to be more sensitive and specific than all B-mode criteria [START_REF] He | Endobronchial ultrasound elastography for diagnosing mediastinal and hilar lymph nodes[END_REF]. Furthermore, the combination of elastography with Bmode criteria has been shown to improve diagnostic accuracy [START_REF] Giovannini | Endoscopic ultrasound elastography for evaluation of lymph nodes and pancreatic masses: a multicenter study[END_REF][START_REF] He | Endobronchial ultrasound elastography for diagnosing mediastinal and hilar lymph nodes[END_REF][START_REF] Saftoiu | Dynamic analysis of EUS used for the differentiation of benign and malignant lymph nodes[END_REF] Some data suggest that certain ultrasound morphological characteristics of lymph nodes on standard B-mode images constitute criteria of malignancy, such as a rounded shape, hypoechogenicity, diameter >1 cm and/or distinct margins. However, these characteristics are relatively non-specific, as they can also be observed in benign nodes [START_REF] Bhutani | A comparison of the accuracy of echo features during endoscopic ultrasound (EUS) and EUS-guided fine-needle aspiration for diagnosis of malignant lymph node invasion[END_REF][START_REF] Fujiwara | The utility of sonographic features during endobronchial ultrasound-guided transbronchial needle aspiration for lymph node staging in patients with lung cancer: a standard endobronchial ultrasound image classification system[END_REF][START_REF] Nakajima | Vascular image patterns of lymph nodes for the prediction of metastatic disease during EBUS-TBNA for mediastinal staging of lung cancer[END_REF].

Strengths and weaknesses of the study

Limitations of the study include that it was based on a single-center cohort, which may limit the extrapolation of our results to other settings. However, the inter-observer agreement of elastography was good. In a multi-center study conducted in 13 centers and 258 patients with pancreatic masses, all video recordings of elastography combined with EUS were examined by two experienced physicians blinded to all clinical information, who were able to establish a diagnosis of benign or malignant disease exclusively on the basis of EUS elastography videos.

Qualitative analysis of the recorded videos revealed a Cohen's kappa coefficient of 0.72 [START_REF] Saftoiu | Accuracy of endoscopic ultrasound elastography used for differential diagnosis of focal pancreatic masses: a multicenter study[END_REF].

Another limitation is that surgical biopsies were not systematically performed to confirm the benign nature of nodes for which TBNA failed to demonstrate any malignant cells; therefore, although this approach corresponds to routine clinical practice, our results should be interpreted cautiously. The prevalence of malignant nodes in our cohort was relatively low (40%), in contrast with other studies on the diagnostic yield of EBUS-TBNA, which have reported malignancy rates of about 60% [START_REF] Herth | Ultrasound-guided transbronchial needle aspiration: an experience in 242 patients[END_REF][START_REF] Yasufuku | Real-time endobronchial ultrasound-guided transbronchial needle aspiration of mediastinal and hilar lymph nodes[END_REF]. This low prevalence could have an impact on statistical analysis of elastography and emphasizes the need for future multi-center trials.

Furthermore, it is noted that the NPV and PPV data are insufficient to conclude with certainty on the nature of the node, especially since the complication rate of the procedure is very low.

As such TBNA cannot be avoided but these data could help the bronchoscopist decide which site to sample first, and may favour a non-invasive follow-up rather than surgical confirmation for negative cases.

Strengths of the study include its innovative nature and the large sample size. Furthermore, some of the statistical approaches used in this study (logistic regression, CART) not only highlight the potential contribution of elastographic variables to the diagnostic approach, but also the potential value of a combined approach including these variables, e.g. a combination of colorimetric score and lymph node diameter, which provides a sensitivity and specificity of 100%. This type of multimodal approach has already been used, and Saftoui et al. [START_REF] Saftoiu | Neural network analysis of dynamic sequences of EUS elastography used for the differential diagnosis of chronic pancreatitis and pancreatic cancer[END_REF][START_REF] Saftoiu | Efficacy of an artificial neural network-based approach to endoscopic ultrasound elastography in diagnosis of focal pancreatic masses[END_REF] used a neural network to achieve a training accuracy of 91.14% (95%CI: 89.87%-92.42%).

Our results obtained with more conventional statistical tools achieved the same level of information, although the CART data were derived from a post hoc analysis and will need further prospective evaluation.

Conclusion

Although the results of this study need to be corroborated by larger scale, multi-center studies, they support the recent European guidelines on ultrasound in general, suggesting that elastography provides complementary data to standard (B-mode) ultrasound imaging and allows more accurate guidance of gastrointestinal EUS-FNA (37).

In the field of respiratory endoscopy, elastography cannot replace histological examination [START_REF] Fournier | Performance of endobronchial ultrasound elastography in the differentiation of malignant and benign mediastinal lymph nodes: results in real-life practice[END_REF] but could provide a particularly relevant contribution to treatment decisions when the node studied has a low clinical and radiological probability of malignancy and when TBNA does not reveal any tumor cells. In this setting, elastographic characteristics in favor of the 'soft' nature of the lesion would avoid the need for immediate mediastinoscopy in favor of a surveillance strategy, while minimizing the risk of allowing progression of a malignant lesion.

Elastography could also assist endoscopists to select aspiration targets corresponding to nodes with the most suspicious elastographic appearance, which would be particularly useful in the context of lymph node staging. Finally, elastography combined with EBUS could guide needle aspiration of the most pathological zone of a given lymph node.

  total of 87 patients participated in the study (no exclusions) and 121 lymph nodes were Of the 61 nodes in which TBNA demonstrated lymph node tissue with no tumor cells, 47 were found to be truly benign (confirmed by mediastinoscopy in 10 cases, by 6 month followup CT in 24 cases, and by the results of cytological or histological samples taken from other targets in 13 cases). The diagnosis remained undetermined for the other 14 nodes, corresponding to cases of metastatic lung cancer (identified by CT-guided needle aspiration or biopsies of spurs) in which mediastinal surgery was not indicated.

	aspirated. The quality of elastographic imaging was insufficient in 8 patients (11 lymph
	nodes). The present analysis was therefore based on 79 patients (58 men, 21 women;
	61.1±11.4 years) and 110 lymph nodes.
	3.2	Lymph node assessment
	Lymph nodes (mean diameter on CT scan: 19±8 mm) were aspirated in the following areas:
	2R (n=1; 1%), 4R (n=36; 32%), 4L (n=10; 10%), 7 (n=26; 23%), 10R (n=6; 5%), 10L (n=1;
	1%), 11R (n=27; 24%), 11L (n=3; 3%).

Malignant cells were identified by TBNA in 44 cases and concluded on the absence of malignant cells in 66 cases, with 5 immediate diagnoses of benign disease and 61 conclusions of normal lymph node tissue (Table

1

). Malignant lymph nodes were significantly larger (23.8±9.6 mm) than benign lymph nodes (15.9±4.7 mm) (p<0.001).

The comparison of malignant and benign lymph nodes (Table

2

) demonstrated that malignant nodes had a higher median SUVmax

(6.8 [4.3±10.4]

) than benign nodes (4.9 [2.9±6.6])

Table 1 .

 1 Histological results obtained by transbronchial fine-needle aspiration (EBUS-

	TBNA)
		Number (%) patients
	EBUS-TBNA result	n=44
	Malignant nodes
	Lung cancers
	Adenocarcinoma	18 (41%)
	Squamous cell carcinoma	9 (20%)
	Non-small cell carcinoma	7 (16%)
	Small cell carcinoma	5 (11%)
	Other	1 (2%)
	Lymphoma	1 (2%)
	Breast cancer metastases	2 (5%)
	Pancreatic cancer metastases	1 (2%)
	Hepatocellular carcinoma metastases	1 (2%)
	Benign nodes	n=66
	Normal lymph node tissue	61 (92%)
	Tuberculosis	2 (3%)
	Sarcoidosis	3 (5%)

Table 2 .

 2 Comparison of elastographic variables and positron emission tomography (PET) data between lymph nodes characterized histologically as benign and those characterized as malignant (110 lymph nodes) Available for only 98 nodes (56 non-malignant, 42 malignant) (became available 2 months after starting the study) **Available for only 73 nodes (38 non-malignant, 35 malignant); SUV: Standardized Uptake Value PET: Positron Emission Tomography

	Benign nodes	Malignant nodes	p

Data are median [interquartile range] or number (percentage). *

DECLARATIONS OF INTEREST

None

FUNDING

None