M.D Raphael Carloni
email: raphaelcarloni@hotmail.com

M.D Christian Herlin

M.D Benoit Chaput

M.D Antoine De Runz

M.D E Watier

MD Nicolas Bertheuil

Scalp tissue expansion above a custom-bone hydroxyapatite cranial implant to correct sequelar alopecia on a transposition flap: a case report

Keywords: cranioplasty, tissue expansion, alopecia, transposition flap, calvarial reconstruction

Scalp tissue expansion above a custom-made hydroxyapatite cranial implant

to correct sequelar alopecia on a transposition flap: a case report

INTRODUCTION

Tissue expansion of the scalp is a well-codified technique used to improve success before cranioplasty after previous infection, tissue avulsion, and/or radiotherapy, [START_REF] Carloni | Soft tissue expansion and cranioplasty: For which indications? J Cranio-Maxillo-fac[END_REF] and to correct sequelar alopecia during second-step surgery. [START_REF] Bilkay | Alopecia treatment with scalp expansion: some surgical fine points and a simple modification to improve the results[END_REF] The scalp is particularly suitable for expansion because the cranial bone provides a solid basis for the expander. No data are available in the literature regarding the safety of expansion above the implant when an alloplastic material (e.g., hydroxyapatite [START_REF] Stefini | Use of "custom made" porous hydroxyapatite implants for cranioplasty: postoperative analysis of complications in 1549 patients[END_REF] , titanium [START_REF] Cabraja | Long-term results following titanium cranioplasty of large skull defects[END_REF] , methyl metacrylate [START_REF] Greene | Onlay frontal cranioplasty using wire reinforced methyl methacrylate[END_REF] ) is used to replace the cranial bone after cranioplasty.

We present the case of a patient who underwent scalp tissue expansion above a custom-made hydroxyapatite implant to correct sequelar alopecia after cranioplasty for dermatofibrosarcoma protuberans.

CASE REPORT

This 30-year-old man had previously undergone a right temporo-frontal craniotomy for resection of temporo-frontal dermatofibrosarcoma protuberans with bone invasion. Coverage of the dura with a transposition flap and no bone reconstruction was performed at the same time. The donor site of the flap, on the vertex, was covered with a skin graft, leaving a sequelar alopecia zone that measured 9 × 13 cm (Fig. 1). Histological findings showed complete excision of the tumor.

Six months later, cranioplasty with a custom-made hydroxyapatite implant was decided on. An incision at the medial edge of the transposition flap provided access to the cranial defect. A rectangular periosteal flap was dissected over the cranial bone defect to expose the dura. Bony edges were sharpened to expose healthy cancellous bone, and the implant was fixed on the bone defect. Dural tenting sutures were performed on the edges of the defect to prevent epidural hemorrhage after the surgery, by fixing dura to the native bone with silk sutures. The postoperative course was free of complications. Although the reconstruction was successful, sequelar alopecia on the vertex remained a major social, psychological, and esthetic concern for the patient. At 7 months after the cranioplasty, we decided to perform soft tissue expansion, with two smooth rectangular expanders placed in the two temporal regions between the galea and the periosteum

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through incisions placed at the lateral edges of the alopecia area of the vertex; a 120-cc expander was used on the left side and a 240-cc expander was used on the right side (Fig. 2). The expander on the right side was partially placed above the cranial implant and under the previous transposition flap. In both cases, filling reservoirs were internal, placed in the subcutaneous layer.

The expanders were filled with normal saline (90 cc on the right side, 40 cc on the left side) at the end of the surgery. Two drains were inserted in the subgaleal pockets and kept in place until the amount of drainage had decreased to 20 cc per day. Antibiotic prophylaxis (cefazolin, 2 g) was administered intraoperatively. Healing was achieved in 15 days. The expanders were filled once per week for 3 months postoperatively. The expanders on the right and left sides were inflated to 355 cc and 130 cc, respectively (Fig. 3). CT was performed before expander placement, 1 day postoperatively, and at the end of the expansion to confirm the absence of fracture or dislocation of the hydroxyapatite implant (Fig. 4). At 1 week after the last inflation, the expanders were removed and two advancement flaps were used to remove the entire alopecic zone of the vertex (Fig. 5). The galea was scored to allow further advancement. No complication occurred during the expansion or postoperatively. The patient was very satisfied with the cosmetic result (Fig. 6).

DISCUSSION

The choice between autologous bone and alloplastic material for bone reconstruction in cranioplasty remains under debate. [START_REF] Schwarz | Cranioplasty after decompressive craniectomy: is there a rationale for an initial artificial bone-substitute implant? A single-center experience after 631 procedures[END_REF] Debate also exists concerning techniques for soft tissue recruitment when tissue is lacking over the scalp. [START_REF] Carloni | Soft tissue expansion and cranioplasty: For which indications? J Cranio-Maxillo-fac[END_REF][START_REF] Leedy | Reconstruction of acquired scalp defects: an algorithmic approach[END_REF]8 Among techniques, tissue expansion has been demonstrated to be safe when performed over the cranial bone, either before the cranioplasty procedure to increase the rate of success [START_REF] Carloni | Soft tissue expansion and cranioplasty: For which indications? J Cranio-Maxillo-fac[END_REF][START_REF] Merlino | Role of systematic scalp expansion before cranioplasty in patients with craniectomy defects[END_REF] or after cranioplasty, away from the implant, to correct sequelar alopecia. [START_REF] Bilkay | Alopecia treatment with scalp expansion: some surgical fine points and a simple modification to improve the results[END_REF][START_REF] Azzolini | Skin expansion in head and neck reconstructive surgery[END_REF] However, no application of this technique above a cranial implant has been described, due to the supposed risk of the procedure. Through this case report, we aimed to show that safe expansion is possible, even in situations in which the only stretchable tissue is partially situated above a cranial implant.

Alopecia of the scalp after cranioplasty is a frequent complaint of patients. It can be created by radiotherapy and infection prior to scalp reconstruction, or as a consequence of soft tissue reconstruction with local or free flaps. Except for the rotational scalp flap, which does not cause alopecia but can be used when only slight tissue recruitment is necessary, 7 these flaps are often unesthetic. For large tissue needs, the choice between flaps 8 and tissue expansion [START_REF] Carloni | Soft tissue expansion and cranioplasty: For which indications? J Cranio-Maxillo-fac[END_REF] Hydroxyapatite implants have been demonstrated to have osteoconductive properties that lead to good osteointegration with the cranial vault. In clinical practice, osteointegration can be checked on cranial scans during patient follow up and is defined as the absence of a radiolucent line at the interface between the living bone and the surface of the implant. [START_REF] Stefini | Use of "custom made" porous hydroxyapatite implants for cranioplasty: postoperative analysis of complications in 1549 patients[END_REF] The porous nature of the implant is supposed to allow ingrowth of osteoprogenitor cells, and increased resistance of the implant. Because hydroxyapatite has the same density as bone on CT scans, this process is difficult to confirm and we cannot say that the implant acquires the same resistance as bone in the months following cranioplasty. However, dislocation or fracture of the implant is very rare. [START_REF] Lindner | Cranioplasty using custom-made hydroxyapatite versus titanium: a randomized clinical trial[END_REF][START_REF] Iaccarino | Preliminary Results of a Prospective Study on Methods of Cranial Reconstruction[END_REF] These properties allowed us to attempt expansion over this kind of implant, with a successful outcome. Indeed, in our patient, the implant provided sufficient strength to support a 355-cc expansion. The main condition to verify before expansion was osteointegration of the implant on the preoperative scan.

The risk of infection associated with expansion, which could contaminate the underlying cranial implant, was prevented by respecting some simple rules: (1) intraoperative administration of a prophylactic antibiotic, (2) rapid drain removal, and (3) separation of the implant and the expander by a periosteal flap during cranioplasty. No specific alloplastic material has been shown to be more sensitive to infection in the literature. [START_REF] Yadla | Effect of early surgery, material, and method of flap preservation on cranioplasty infections: a systematic review[END_REF][START_REF] Reddy | Clinical outcomes in cranioplasty: risk factors and choice of reconstructive material[END_REF] Estimated infection rates are 2% for hydroxyapatite implants [START_REF] Stefini | Use of "custom made" porous hydroxyapatite implants for cranioplasty: postoperative analysis of complications in 1549 patients[END_REF] and 24% for expanders. [START_REF] Cunha | Tissue expander complications in plastic surgery: a 10-year experience[END_REF] Tissue expansion must be chosen only in situations in which the scalp has healed completely because wounds could be the port of entry for bacteria, which could contaminate the expander. [START_REF] Carloni | Reconstructive approach to hostile cranioplasty: A review of the University of Chicago experience[END_REF] When the scalp has not yet healed, waiting for complete healing with dressings or the choice of another reconstructive method is preferable, with tissue expansion performed once healing is

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Other reported complications of tissue expansion include exposure, rupture of the expander, and hematoma. [START_REF] Cunha | Tissue expander complications in plastic surgery: a 10-year experience[END_REF] The choice of expander size depends on the size of the defect and the location of the alopecia zone to treat. For round expanders, the tissue gain obtained with expansion corresponds approximately to the radius of the expander. [START_REF] Carloni | Soft tissue expansion and cranioplasty: For which indications? J Cranio-Maxillo-fac[END_REF] For rectangular expanders, the gain is more difficult to predict. For the present patient, we chose two rectangular expanders to expand the two temporal regions. No difference in complications according to expander shape has been reported. However, the use of fewer expanders seems be associated with a lower frequency of complications. [START_REF] Leedy | Reconstruction of acquired scalp defects: an algorithmic approach[END_REF][START_REF] Wang | Complications in tissue expansion: an updated retrospective analysis of risk factors. Handchir Mikrochir Plast Chir Organ Deutschsprachigen Arbeitsgemeinschaft Für Handchir Organ Deutschsprachigen Arbeitsgemeinschaft Für Mikrochir Peripher Nerven Gefässe Organ[END_REF] Expanders must be placed as high as possible on the scalp for two reasons: the higher temporal regions and the vertex are easier to stretch, and such placement avoids the patient's sleeping on the expanders during the night, thereby diminishing the risk of exposure.

Although the filling reservoir can be placed externally, placement under the skin is more comfortable for the patient. Our expansion protocol did not differ from the protocols described in the literature. In our case, we stopped expander inflation when the filled volume slightly exceeded 150% of its capacity on the right side and 100% of capacity on the left side. Expanders can be overinflated to 150% of their capacity to improve tissue gain. [START_REF] Carloni | Soft tissue expansion and cranioplasty: For which indications? J Cranio-Maxillo-fac[END_REF] Another option to improve tissue gain consists of scoring of the galea. This procedure could compromise the perfusion of the advancement flaps. Thus, we perform it only when necessary.

Other techniques described in the literature to correct sequelar alopecia of the scalp include external tissue expansion [START_REF] Reinard | Preoperative external tissue expansion for complex cranial reconstructions[END_REF] and hair grafting in the alopecia zone. 19 In our experience, the outcome of hair grafting is very disappointing in large zones of scar tissue, but this technique can be attempted in small zones, such as enlarged scars. Two possibilities exist in this situation.

When possible, a tricophytic technique should be attempted first. 20 When scar enlargement is important, making a tricophytic suture difficult, or when a new suture in the area is risky for healing reasons, a hair graft with follicular unit extraction 19 should be attempted.

CONCLUSION

Tissue expansion remains the gold standard for the treatment of sequelar alopecia after cranioplasty. This procedure may be of concern to the physician when performed above hydroxyapatite implants because of the risk of infection and rupture of the cranial implant.

Precautions to prevent these issues include a preoperative check of the osteointegration of the

  must be M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT discussed because both options have advantages and disadvantages. Based on our experience, we recommend that scalp expansion be attempted first, except in situations in which an open wound still exists or rapid coverage is necessary. 11 This choice allows the achievement of a more esthetic reconstruction after the first surgery, providing natural hair-bearing skin to correct a tissue defect. When large local flaps of the scalp, such as transposition flaps or bipedicled flaps, have been used in the first surgery, most of the hairy tissue lies above the cranial implant and the only solution for the treatment of alopecia with expansion is to place an expander above the cranial implant.

  Follicular unit extraction. Facial Plast Surg FPS 2008;24:404-413. 20. Ahmad M. Does the trichophytic technique have any role in facial wound closure? A hypothesis. J Plast Reconstr Aesthetic Surg JPRAS 2009;62:662.

Figure 1 .

 1 Figure 1. Preoperative picture of the patient presenting with a sequelar alopecia of vertex after a transposition flap of the scalp.

Figure 2 .

 2 Figure 2. Photo of the two rectangular expanders.

Figure 3 .

 3 Figure 3. Picture of the patient after maximal inflation of the expanders.

Figure 4 .

 4 Figure 4. Computed tomographic scan after maximal inflation of the expanders. The scan shows an osteointegration of the hydroxyapatite implant and the absence of fracture or dislocation.

Figure 5 .

 5 Figure 5. Intraoperative view after removal of the expanders.

Figure 6 .

 6 Figure 6. Postoperative picture of the patient after correction of the alopecia.

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implant; a 6-month interval between cranioplasty and expansion; separation of the expander from the implant using periosteum; antibiotic prophylaxis and rapid drain removal.

DISCLOSURES

The authors have no disclosures to declare.

Abbreviations computed tomography (CT)