Morgane Dachary
email: morgane.dachary@culture.gouv.fr

François-Xavier Chauvière
email: hauterive.francois-xavier.chauviere@ne.ch

Frédéric Plassard
email: frederic.plassard@wanadoo.fr

The Middle/Upper Magdalenian transition at Bourrouilla cave in Arancou (Pyrénées-Atlantiques, France): portable art and context-induced considerations

Keywords: Upper Magdalenian, Middle Magdalenian, Pyrenees, portable art, Bourrouilla cave, Transition

Bourrouilla cave in Arancou (Pyrénées-Atlantiques region, France) is a Paleolithic dwelling site with occupations mostly assigned to the Upper Magdalenian with harpoons. The archeological richness of the levels, the good preservation state and diversity of the remains, which include portable art, make it a major site of the western Pyrenees. It has been excavated meticulously with a fine recording of data for about twenty years. So far, available data for occupations older than the Upper Magdalenian are rare. However, the discovery at the back of the cave of a rib fragment decorated with a particularly detailed horse head feeds our considerations. By its style, this figuration differs much from art works assigned to the Upper Magdalenian; it has obvious connections with the Middle Magdalenian Pyrenean art. This discovery is consistent with the presence in the spoil of a clandestine excavation of half-round

Introduction

Discovered in 1986 at the same time as a clandestine excavation, Bourrouilla cave site in Arancou has been subjected to almost uninterrupted archeological excavations since the early 1990s.

To date, the discovered archeological material can be divided into three lots: (1) remains collected during the sieving and sorting of the clandestine excavation spoil, (2) material from a test pit dug in front of the entrance porch in 1990-1991 and (3) results from the excavations undertaken since 1998. Most of the remains from the first two lots were published in 1999 (Chauchat et al.) while the excavations undertaken since 1998 have been published regularly (Dachary 2002;[START_REF] Dachary | La grotte de Bourrouilla à Arancou (Pyrénées-Atlantiques): bilan des fouilles 2002 à 2004[END_REF]2006;[START_REF] Dachary | Les Magdaléniens des Pyrénées occidentales. Réflexions sur l'exploitation d'un territoire[END_REF][START_REF] Dachary | La grotte Bourrouilla à Arancou: une puissante stratigraphie au service de la perception de la fin du Magdalénien pyrénéo-cantabrique. Acte de la Table Ronde SPF «Les sociétés Paléolithiques d'un grand Sud-Ouest: nouveaux gisements, nouvelle méthodes[END_REF]2013;2014;[START_REF] Pétillon | Technological evolution of hunting implements among Pleistocene hunter-gatherers: Osseous projectile points in the middle and upper Magdalenian (19-14 ka cal BP)[END_REF][START_REF] Daulny | Approche comportementale du Magdalénien d'après l'étude techno-fonctionnelle de l'outillage hors silex. La grotte de Bourrouilla (Arancou, Pyrénées-Atlantiques, France)[END_REF][START_REF] Aurière | Art mobilier inédit du gisement de Bourrouilla à Arancou: données techno-stylistiques et chrono-culturelles[END_REF][START_REF] Plassard | Nouvelles découvertes d'art mobilier dans le Magdalénien de Bourrouilla (Arancou, Pyrénées-Atlantiques)[END_REF][START_REF] Rivero | L'apprenti préhistorique. Appréhender l'apprentissage, les savoirfaire et l'expertise à travers les productions techniques des sociétés préhistoriques[END_REF][START_REF] Szmidt | Harfang, Renne et Cerf: nouvelles dates 14C par SMA du Magdalénien supérieur du Bassin aquitain au Morin (Gironde) et Bourrouilla (Pyrénées-Atlantiques)[END_REF]). Fieldwork has highlighted Holocene, especially Mesolithic, as well as Protohistoric and Medieval occupations. However, most of the research to date has documented a series of settlements assigned to the Upper Magdalenian that features an abundant lithic industry and a bone industry with harpoons. Nevertheless, in the last excavations it has been possible to reach the levels underlying the Upper Magdalenian inside the cave. Rare remains are known for the moment including a remarkable horse head engraved on a bone fragment. Besides their intrinsic interest, they are presented here alongside a synthesis about the Upper Magdalenian of the site because of the relationship they probably have with some objects from the clandestine excavation spoil and of wider questioning about the end of the Middle Magdalenian and the beginning of the Upper Magdalenian.

The site

Bourrouilla cave is located in the municipality of Arancou (Pyrénées-Atlantiques region, France), 7 km south-west of the Pastou Cliff (Sorde-l'Abbaye, Landes). It is a low-altitude site (about 60 m NGF -General Levelling of France) set in the hilly reliefs of the western Pyrenees foothills. The cave opens to the south-east a short distance from the Lauhirasse stream, a tributary of the right bank of the Bidouze River. It is a small cave, about twelve meters deep today. The ribbed porch was 3.50 m high in the Magdalenian and about 2 m wide. It gives access to a 6 to 7 m long rectilinear corridor, whose vault lowers steadily, and which leads to a small chamber, about 3 m by 4 m. Four areas were highlighted during the archeological excavations:

-The Outer Zone, tested then excavated in squares J, K, L 25 to 28. The top of the sequence gave some evidence of occupations assignable to the Neolithic and/or to Protohistory. Then a thin Mesolithic level [START_REF] Dachary | Les occupations mésolithiques de Bourrouilla à Arancou (Pyrénées-Atlantiques)[END_REF]) is followed by a sparse level (Ensemble A) characterized by backed points fashioned from a small blade production, by the absence of bone industry and the persistence of the Reindeer. It is described as Final Magdalenian [START_REF] Dachary | Une perception affinée du Magdalénien des Pyrénées occidentales à partir des travaux récents. Acte du Colloque International d'Archéologie de Puigcerdà[END_REF][START_REF] Dachary | Deuxième moitié et fin du Paléolithique supérieur. Pour une confrontation entre le modèle classique et les perceptions interdisciplinaires actuelles sur le thème des unités, continuités et discontinuités[END_REF]. The underlying Ensemble B documents an Upper Magdalenian with harpoons, in which Red Deer is the main game [START_REF] Chauchat | L'habitat Magdalénien de la grotte Bourrouilla à Arancou (Pyrénées Atlantiques)[END_REF][START_REF] Dachary | La grotte Bourrouilla à Arancou: une puissante stratigraphie au service de la perception de la fin du Magdalénien pyrénéo-cantabrique. Acte de la Table Ronde SPF «Les sociétés Paléolithiques d'un grand Sud-Ouest: nouveaux gisements, nouvelle méthodes[END_REF] -The Corridor (bands 22 to 18). So far, fieldwork has not identified levels in place in this part. Given the geometry of the deposits, the hypothesis of a massive sinkhole probably explains the absence of Pleistocene level in this area. The first consequence of this observation is the lack of any stratigraphic continuity between the Vestibule and the Back Chamber. Therefore, the analysis of the prehistoric occupations at the site is based on two distinct stratigraphies: the first one, described above, concerns the exterior and the Vestibule, while the second one (see below) is limited to the Back Chamber.

-The Back Chamber (bands 17 to 14). This area was damaged by a clandestine excavation before the discovery of the site in 1986. Eleven radiocarbon dates (Table 1) make it possible to situate the Magdalenian occupations of the site. Six of them (Gif 9986, 10002, 10234, 10235, 10254, 10255) were obtained by counting on bone samples taken in the test pit in the Outer Zone. The other dates, obtained by AMS, document SU 2007AB in the cave (OxA 19696, 19697, 19698), and Ensemble A in the Vestibule (OxA 29930-31 and OxA 29932). These results confirm the reliability of the stratigraphy through field observations and geoarcheological and taphonomic analyses (Dachary et al. submitted).

The Upper Magdalenian in Arancou: review

Lithic and bone equipment

The Upper Magdalenian at Bourrouilla is known today through the excavation of Ensemble B (Outer Zone and Vestibule) and of SU 2007 (Back Chamber). The faunal range of these occupations is dominated by the Red Deer (Cervus elaphus) together with the Reindeer. Note, however, the exceptional number of remains of Snowy Owl (SU 2007 AB) or Fish (SU 2007 E) in some sub-ensembles of SU 2007. The lithic industry is marked by the predominance of lamellar tools, together with the common toolkit in which burins and borers are dominating over side scrapers, which are few in number. The highly fragmentary aspect of the operative chains also indicates brief and repeated frequentations. The bone industry is showing Reindeer and Red Deer antler exploitation, with harpoons and spearheads, and a number of technical pieces. Bone was also exploited for the manufacture of needles, smoothers and, to a lesser extent, awls. The discovery of a fragment of smoother in SU 2007 E has allowed making a refit with two pieces from the clandestine excavation spoil. This is a major result at the scale of the site, as it confirms the assignment of these objects, sometimes decorated, to the Upper Magdalenian [START_REF] Aurière | Art mobilier inédit du gisement de Bourrouilla à Arancou: données techno-stylistiques et chrono-culturelles[END_REF]. As for ornaments, sawn teeth, pierced teeth, a hematite bead and probably a shark tooth were found.

Beyond this summary description of the remains, note also that the stripping of SU 2007 E on about 3 m² has identified a layer of ocher together with a concentration of "extraordinary" remains (in the meaning of [START_REF] Chiotti | Statut des objets «extra-ordinaires» du Gravettien final de Pataud (Les Eyzies-de-Tayac, Dordogne) : objets abandonnés dans l'habitat ou dépôt intentionnel ?[END_REF] such as a pecten with ocher on its internal side (container?), a flint color crusher, and an abnormal density of bone industry and portable art remains [START_REF] Dachary | Le contexte des oeuvres d'art mobilier dans le Magdalénien supérieur de la grotte Bourrouilla (Arancou, Pyrénées-Atlantiques, France)[END_REF]. Lastly, fieldwork has identified several nested hearths that are under study.

Portable art

SU 2007 and, to a lesser extent, Ensemble B are documenting a varied production of portable art works. While the clandestine excavation spoil exclusively yielded decorated objects on hard animal material, most of them fashioned on split ribs (smoothers and pendants), stratigraphic excavations of the Vestibule and of the levels in place in the Back Chamber considerably broadened the range of symbolic productions. Figurative, abstract and indeterminate decorations are visible on sandstone plaquettes, fragments of limestone identical to the bedrock and bone objects [START_REF] Aurière | Art mobilier inédit du gisement de Bourrouilla à Arancou: données techno-stylistiques et chrono-culturelles[END_REF][START_REF] Plassard | Nouvelles découvertes d'art mobilier dans le Magdalénien de Bourrouilla (Arancou, Pyrénées-Atlantiques)[END_REF]. A certain iconographic diversity and the production of images of varying dimensions respond to the variety of the blanks. In addition, while the most careful and better done works correspond to finished objects, more unskillful works were created on unprepared blanks [START_REF] Plassard | Nouvelles découvertes d'art mobilier dans le Magdalénien de Bourrouilla (Arancou, Pyrénées-Atlantiques)[END_REF].

A coherent picture of the Upper Magdalenian graphic productions of the site can be drawn from the obvious similarities between part of the objects from the clandestine excavation and some remains discovered during the excavations. Firstly, the series of smoothers and pendants on hemi-ribs, decorated with very small size animal figures and abstract patterns, is remarkable. These objects were published 20 years ago and made the reputation of the site.

Stylistically, they fit perfectly into the range of the Magdalenian portable art of the Pyrenees and there are equivalents at Lortet or Gourdan, for example. Animal representations are both easily identifiable and often little detailed. These synthetic drawings are also found on a tube made from a Snowy Owl long bone diaphysis decorated with two horses and a crane. SU 2007 also yielded works on unprepared bone, showing less technical mastery, but with the same style conventions. Sandstone plaquettes and limestone blocks, often engraved with abstract patterns but also with animal figurations, were also discovered.

In total, the figurative art of Bourrouilla is made of 32 pictures on 17 blanks. 21 images on 9 bone pieces are coming from the clandestine excavation, 8 figurations on 5 objects (4 bone pieces and one sandstone plaquette) have been found in SU 2007 while the last 3 are from Ensemble B (one bone blank and two lithic blanks).

At the transition between Middle Magdalenian and Upper

Magdalenian: a working hypothesis

In Arancou, the presence of occupations earlier than the Upper Magdalenian (with harpoons) has been considered right from the publication of the first article [START_REF] Chauchat | L'habitat Magdalénien de la grotte Bourrouilla à Arancou (Pyrénées Atlantiques)[END_REF], both under the porch of the cave and inside it, on the basis of stratigraphic arguments, radiocarbon dating and diagnostic remains.

Archeological context

The Outer Zone: Ensemble C

Immediately in front of the porch, the outside test pit reached sedimentary Ensemble C, directly underlying Ensemble B. Known on about 2m², it is characterized at the sedimentary level by a rarefaction of the coarse fraction at the expense of a homogeneous silt-clay sediment. The excavation did not reach the base of this poor archeological ensemble [START_REF] Chauchat | L'habitat Magdalénien de la grotte Bourrouilla à Arancou (Pyrénées Atlantiques)[END_REF], which yielded a large proportion of truncated microliths, associated with one scalene bladelet and three scalene triangles (Fig. 2, No. 2-6). These elements would indicate a proximity of Ensemble C with assemblages assigned elsewhere to the Middle Magdalenian [START_REF] Chauchat | L'habitat Magdalénien de la grotte Bourrouilla à Arancou (Pyrénées Atlantiques)[END_REF]. The radiocarbon dates around 12,700 BP obtained for the B3-C1-C4 layers are pointing in the same direction (Fontugne and Hatté in Chauchat 1999).

In the bone industry register, two categories of cervid antler objects (harpoon-type barbed elements and fork-based points) seem to be mutually exclusive within ensembles B and C (Bonnissent and Chauvière in [START_REF] Chauchat | L'habitat Magdalénien de la grotte Bourrouilla à Arancou (Pyrénées Atlantiques)[END_REF]). Thus, we can note:

-In Ensemble B, the presence of 9 harpoon-type barbed elements and the lack of fork-based points;

-In Ensemble C (C1 and C2), the presence of two fork-based points (Fig. 2, No.1) and the lack of harpoon-type barbed elements.

The fork-based point type refers to the transition between the late phase of the Middle Magdalenian and the early stages of the Upper Magdalenian (i.e. [START_REF] Pétillon | Des Magdaléniens en armes[END_REF][START_REF] Pétillon | Les pointes à base fourchue de la zone pyrénéo-cantabrique : un objet à la charnière entre Magdalénien moyen et Magdalénien supérieur ? Frontières naturelles et frontières culturelles dans les Pyrénées préhistoriques[END_REF][START_REF] Pétillon | Technological evolution of hunting implements among Pleistocene hunter-gatherers: Osseous projectile points in the middle and upper Magdalenian (19-14 ka cal BP)[END_REF].

Inside the cave: data from the clandestine excavation and SU 2010

Various archeological remains from the clandestine excavation have also allowed considering the existence of assemblages older than the Upper Magdalenian inside the cave. These are scalene microliths, four fork-based points (Fig. 2, No. 11-13), two of which bear traces of resection, and fragmentary half-round rods of the Isturitz type (Fig. 2, No. 10). The question that now arises is whether (a) stratified level(s) is/are still in place at the back of the cave with this type of remains.

Originally described on the clandestine excavation sections, SU 2010 has been excavated since 2012. Immediately underlying SU 2007, it differs from it by a yellow color and the absence of ferro-manganic deposit. The coarse fraction, less abundant than in SU 2007, consists of large stones and some limestone blocks, often burned. They have blunt edges but their surface is not powdery. The excavated surface is still too small to discuss both the spatial organization of the remains and the very nature of this ensemble: flood level accumulation lens, hearth, etc.

Data from portable art

Decoration of the half-round rod

We are returning here to the description of the object we have already published [START_REF] Plassard | Nouvelles découvertes d'art mobilier dans le Magdalénien de Bourrouilla (Arancou, Pyrénées-Atlantiques)[END_REF]: "This is a mesial fragment of a half-round rod (Fig. 2, No. 9) discovered in SU 2010. The lower surface is much smoothed, concave and bears oblique parallel rectilinear incisions. The latter were intended to stick the object onto a similar volume. One of the extremities of the fragment in our possession bears a decoration consisting of two lateral patterns. They are identical on both sides and are made up of a series of short cross-hatched lines (2 mm), which are delimited at the top by a rectilinear or slightly curved line." In its current state, this bone fragment is 90 mm long, 33 mm wide and 9 mm thick. It was identified as a rib fragment (Aude Chevalier, UMR 7041, ArScAn), based on the presence of a straight edge, a unique and regular convexity of the upper side and the partial presence of the lower side, allowing the reconstruction of part of the profile (Fig. 4). The decorated area bears no trace of scraping prior to engraving; one of the extremities has the features of a serrated break on dry bone, and the other shows a blunting of indeterminate origin (use or taphonomy).

The horse engraving

The external side (best preserved) shows the head and neck of a horse. The outline of the head, the nostril, the mouth, the eye, one ear, the forelock, the mane in hatching, the lower jaw also done in hatching and the beginning of the back and chest lines, interrupted by the fracture of the piece, can be read without difficulty (Fig. 4 & Fig. 5). A line separates the tip of the nose from the rest of the head and probably indicates a shade of coat.

Detailed observation with the naked eye and under a stereo microscope makes it possible to precise the tracing of the engraved lines. Thus, the mane consists of two series of short hatchings interlocked into one another with slightly different orientations as if from dissimilar workmanships. A first series of little marked lines, slightly oblique towards the back, is intersected by other hatchings, more vertical or bent forward, and much more pronounced.

Much below these hatchings, an almost straight line is probably the neck, from the base of the ear to the shoulder. At this level, it meets a curved line that could indicate the shoulder line (or shoulder band) and that is joining the beginning of the back line.

The single ear is located in front of the mane and at the same level. The forelock is indicated in front of it, made of five slightly oblique downwards hatchings. The forehead is clearly convex, and is continued by a rectilinear chanfrin to the tip of the nose. This initially rather deep and symmetrical tracing is clearly asymmetrical in its lower part. Parasitic lines on the outside of the contour are showing the use of an irregular point. The nostril is placed quite high above the tip of the nose. It is indicated by a U-shaped line closed by its juxtaposition to the contour tracing. A line draws the upper lip and the mouth and another one the chin. From the back of the nostril to the back of the mouth, a last tracing reflects the dividing line between the short coat of the muzzle and the denser one of the rest of the head. The intermandibular region and the lower jaw are represented by a series of very regular and tight hatchings that join the throat line. A shallower line on the inside of the cheek is superimposed on the hatchings of the lower jaw and forms the upwards limit. Starting halfway between the ear and the throat, the line of the neck and chest continues to the broken edge of the blank. This line, obviously obtained by several slightly misaligned passing of the tool, contrasts with the minutia of the hatching of the lower jaw. The eye itself is simply indicated by two small opposite arcs of a circle.

Discussion: Comparisons with the Upper Magdalenian at Bourrouilla and to the regional scale

The decoration of the half-round rod has no equivalent to date and cannot be used to set out arguments about the chrono-cultural assignation of SU 2010. However, two types of comparisons can feed the debate; on the one hand with the other figurations of horses from the Upper Magdalenian at Bourrouilla, on the other hand with Magdalenian portable art works from other Pyrenean sites. At the scale of the site, we know of 4 horses drawn on two objects (Fig. 6). The first one comes from the clandestine excavation spoil; it is a bird bone tube (Snowy Owl) on which two top to tail horse heads are depicted with a possible crane [START_REF] Chauchat | L'habitat Magdalénien de la grotte Bourrouilla à Arancou (Pyrénées Atlantiques)[END_REF]. These small-size images are little detailed and mostly treated as linear contours. The second one is a Red Deer rib discovered in excavation in SU 2007, decorated with two horses following each other, one being reduced to the anterior part of the head [START_REF] Aurière | Art mobilier inédit du gisement de Bourrouilla à Arancou: données techno-stylistiques et chrono-culturelles[END_REF].The most complete horse is a linear contour with an absolute profile. The crested mane and the lack of hatching for the lower part of the head are remarkable. The second subject, reduced to the head due to the break of the piece, only shows the chanfrin, one eye and the beginning of the intermandibular region. It is difficult to discuss the style of such a fragmentary image, but it seems in keeping with its neighbor. These four images fit well into the stylistic canons of the Upper Magdalenian (Rivero and Sauvet 2014: 73). On the opposite, the horse we are describing here is totally at odds with this type of representation; it features a larger subject, an increased anatomical accuracy, the use of hatching for the mane, the forelock, the intermandibular region and the jawbone.

A further reading level is provided by studying the degree of technical mastery of the engravers through applying the analysis grid proposed by O. [START_REF] Rivero | L'apprenti préhistorique. Appréhender l'apprentissage, les savoirfaire et l'expertise à travers les productions techniques des sociétés préhistoriques[END_REF]. This author highlights three levels of technical expertise from the "highly expert engravers" up to the "beginners with little expertise", including the "apprentice engravers" whose production shows an intermediary level. In this perspective, the Red Deer rib decorated with two horses from SU 2007 would be the work of a beginner engraver, which could be confirmed by the lack of preparation of the blank. Indeed, aside a quickly abandoned attempt at re-splitting, this piece shows no trace of scraping or shaping before engraving. The same type of analysis can be carried out on the horse studied in this article. Although it does not appear to have been prepared before engraving, the technical analysis of the tracing would indicate the work of an "intermediary level engraver." Indeed, the highly dissymmetrical profile of the tracing of the tip of the nose as well as the inability to deepen the chest line by passing over exactly the same grove associated to a good mastery of proportions and to a high number of anatomical details would show the work of an experienced engraver but still in apprenticeship. Comparing the horse figuration described here with the regional corpus inevitably leads to the Pyrenean Middle Magdalenian, even though style data do not offer a sufficiently fine resolution to decide between Late Middle Magdalenian and Early Upper Magdalenian. In other words, it is not presently possible to know if the rupture in style is synchronous with the appearance of the forked bases or of the harpoons. The factor analysis carried out by O. [START_REF] Rivero | Defining Magdalenian cultural groups in Franco-Cantabria by the formal analysis of portable artworks[END_REF] on a sample of 273 horse figurations from Magdalenian portable art identifies styles that are unevenly distributed over time and space. Although the analysis tools used are of a statistical nature, and therefore only indicate trends that do not exclude some exceptions, one of the three groups highlighted by PCA is strongly associated with the Middle Magdalenian of the Pyrenees. Yet, this group brings together horses figurations that share numerous stylistic common points with the one we studied: abundance of anatomical details, intensive use of hatching, indication of the coat limit at the tip of the nose (Fig. 7). But the recent discovery of highly spectacular horse figurations at Le Rocher de l'Impératrice site (Finistere area, France) shows that a realistic style persisted beyond the Middle Magdalenian until the early Azilian [START_REF] Naudinot | Divergence in the evolution of Paleolithic symbolic and the technological systems: The shining bull and engraved tablets of Rocher de l'Impératrice[END_REF]. This implies we must have caution. However at Le Rocher de l'Impératrice, we can note that the eye is not indicated, and above all that the numerous hatchings are more a process of filling-in the images than a graphic solution to creating contours as observed classically in the Middle Magdalenian. 1991). 4-Labastide (after [START_REF] Simonnet | Art mobilier et art pariétal à Labastide[END_REF].

  . Reached only in KL 25 in the test pit, Ensemble C is more difficult to assign: Late Middle Magdalenian or Early Upper Magdalenian? -The Vestibule, excavated in K and L 23-24. At the top of the sequence, the remains of a (medieval?) lime kiln were found. The first preserved Paleolithic levels correspond to Ensemble A, defined outside the cave. Then comes Ensemble B. The excavations of this area have not yet reached Ensemble C.

  It is therefore difficult to reconstruct the archeological filling before the contemporary interventions; however it should be noted that several stratigraphic units (SU) are clearly visible on the edge of the clandestine excavation, such as SU 2002 (pit with Mesolithic remains, Dachary et al. 2013), SU 2007 whose excavation showed Upper Magdalenian occupations, and SU 2010, previously intact, and whose archaeological material seems to document an older phase than the classical Upper Magdalenian with harpoons.

Figure 1 :

 1 Figure 1: Bourrouilla cave. Plan of the cave and synthetic stratigraphic section of the site. The green area on the section indicates several possibly post-Paleolithic Stratigraphic Units (SU).

  The stratigraphic position of SU 2010, the presence of a half-round decorated antler rod fragment -undocumented object category in the overlying SU 2007 or in Ensemble C -, the lack of harpoon-type barbed elements and the predominance of the Reindeer and the Horse among the hunted fauna, the virtual absence of fish fauna remains -so abundant in SU 2007and the quantitatively significant presence of scalene bladelets (Fig.2, No. 7 and 8) at the base of SU 2007 (SU 2007 F) are questioning the existence, in stratigraphy and inside the cave, of a phase connected to the beginning of the Upper Magdalenian or to the end of the Middle Magdalenian in Arancou.Data from the avifauna range and the lithic industry techno-typological features, highly ubiquitous, do not make it possible to decide between these two hypotheses.What about elements from the analysis of the portable art? This is what we intend to present below.

Figure 2 :

 2 Figure 2: Ensemble C: 1 -fork-based spearhead; 2 -"grain de mil" flint backed bladelet; 3 -scalene bladelet; 4 -scalene triangle; 5 & 6 -truncated backed bladelets. SU 2007F: 7 & 8 -scalene bladelets. SU 2010: 9 -decorated half-round rod. Clandestine excavation: 10 -fragment of half-round rod of the Isturitz type; 11 to 13 -fork-based spearhead. Drawing of the bone industry: F.-X. Chauvière. Drawing of the lithic industry: Morgane Dachary. Photo: A. Roussot & F. Plassard.

  Discovered at the base of a sediment sample taken for the study of the hearths in SU 2007, this fragment of large herbivore rib belongs to the top of SU 2010. Its state of fragmentation immediately necessitated a restoration (Fig. 3). Funded by the Ministry of Culture and conducted by Marielle Boucharat (Artemuse Association), this intervention made possible the handling and study of this exceptional piece.

Figure 3 :

 3 Figure 3: ARA15-US2010. Large herbivore rib decorated with a horse head before restoration (© F. Plassard).

Figure 4 :

 4 Figure 4: ARA15-US2010. Large herbivore rib decorated with a horse head after restoration (© F. Plassard).

Figure 5 :

 5 Figure 5: SU 2010. Tracing of the horse head engraved on a rib fragment (Tracing F. Plassard).

Figure 6 :

 6 Figure 6: Top. Photograph and tracing of the unrolled decoration of a Snowy Owl bone diaphysis with two top to tail horse heads and one wading bird (crane?) (Photograph and drawing A. Roussot). Bottom. Photograph and tracing of two horses engraved on a Red Deer rib discovered in SU 2007 (Photograph F. Plassard, Drawing L. Aurière).

Figure 7 :

 7 Figure 7: Horses from the Pyrenean Middle Magdalenian. 1-Isturitz, Saint-Martin Chamber (after Saint-Périer, 1930). 2-Isturitz, Layer E (after Passemard, 1924). 3-Bédeilhac (after Jauze and Sauvet,

Table 1 -

 1 Radiocarbon dating of Bourrouilla's Magdalenian levels after Fontugne and Hatté in[START_REF] Chauchat | L'habitat Magdalénien de la grotte Bourrouilla à Arancou (Pyrénées Atlantiques)[END_REF][START_REF] Szmidt | Harfang, Renne et Cerf: nouvelles dates 14C par SMA du Magdalénien supérieur du Bassin aquitain au Morin (Gironde) et Bourrouilla (Pyrénées-Atlantiques)[END_REF] et Barshay-Szmidt et al. 2016. Datings are calibrated with the

	IntCal 13 curve (Reimer et al. 2013), the Calib 6.0.1 software (Stuiver and Reimer 1993) and given
	with 2 sigma.

Acknowledgements:

We wish to thank Estelle Bougard for the English translation of this text as well as the reviewers working with the publisher of this volume. Their constructive critics led us to precise some points of this article and to add figures.

10940 ± 45 12706 -12932 Ensemble A Red deer (AMS) OxA29930-31 12013 ± 36 13751 -13997 Layer B2 (counting) Gif

Bourrouilla site has so far yielded remains of occupations assignable mainly to the Upper Magdalenian with harpoons. The richness of the levels and their stratigraphic integrity as well as the state of conservation of the remains and their diversity make it possible to characterize this chrono-cultural phase, and even to apprehend its internal evolution (Dachary et al., submitted). The presence of hearths, still under study, and of at least one layer of remains stripped on a sufficient surface, also allow addressing the question of the activities carried out at the site and of their spatial distribution in the cave. The portable art, mainly done on bone, is remarkable by its quality and its iconographic diversity [START_REF] Plassard | L'art mobilier d'Arancou : drôle de choix ! In[END_REF].

In Arancou, the occupations of the site during the Upper Magdalenian are well documented, both in the Outer Zone of the cave and inside, within a stratigraphy with a high level of chronological resolution. If the clues of an earlier phase are still rare, they nevertheless do exist. Indeed, the radiocarbon dates and the lithic toolkit features would point to the actual presence of the middle phase sensu lato of the Magdalenian. Being "transitional" objects, the fork-based points found in the clandestine excavation and in Ensemble C indicate even more precisely the end of the Middle Magdalenian and the beginning of the Upper Magdalenian in Arancou. Because it also fits perfectly into the stylistic canons of the Pyrenean Middle Magdalenian, the engraved horse head described in this article is a significant argument for identifying this chrono-cultural phase in stratigraphy inside the cave.

The continuation of the excavations should make it possible to test this hypothesis. If SU 2010 is well preserved and as rich as SU 2007 (Upper Magdalenian), Bourrouilla site will probably shed new light on the transition between the Middle Magdalenian and Upper Magdalenian. The issue is all the greater since few sites benefiting from modern excavations seem able to document this chrono-cultural phase.


Jean-Baptiste B Philippe
email: jean-baptiste.philippe@etud.univ-angers.fr

A Lemoult

J Riou

M Sarfati-Lebreton

S Mucci

Feasibility criteria for total thyroidectomy in outpatient surgery Critères de faisabilité d'une thyroïdectomie totale en chirurgie ambulatoire

Keywords: outpatient, risk factors, surgery, thyroid Mots clés : ambulatoire, chirurgie, facteurs de risque, thyroïde

Introduction:

France is pursuing a policy of cutting healthcare costs, and outpatient surgery is one of the objectives of this policy. Thyroid surgery could be suitable for outpatient management, provided there is an appropriate patient selection process. The aim of this study was to assess the risk factors for postoperative complications in total thyroidectomy (TT). Design: A single-center observational study was carried out from January 2010 to December 2015. Method: Correlations between, on the one hand, age, gender, obesity, history of surgery, antiplatelet and/or anticoagulation treatment, the surgeon's experience, surgery time, repeated lymph node dissection, and surgical indication (cancer, lymphocytic thyroiditis, Graves' disease or multinodular goiter) and, on the other hand, onset of postoperative complications (postoperative hypocalcemia, uni-or bi-lateral lesions of the recurrent laryngeal nerves, and premature compressive hematoma) were assessed. Results: 424 consecutive TTs were included. 85 patients showed postoperative hypocalcemia (20.04%), 18 recurrent laryngeal nerve lesion (4.25%), and 4 compressive cervical hematoma (0.94%). Overall morbidity was 24.06%. Risk factors identified for postoperative hypocalcemia comprised: female gender [OR=3.2584; 95%CI (1.5500-7.7515); P=0.0036], surgery time [OR=1.0095; 95%CI (1.0020-1.0172); P=0.0129], and surgical indication for benign adenoma [OR=5.0642; 95%CI (1.7768-14.5904); P=0.0022]. None of the study variables emerged as risk factors for recurrent laryngeal nerve lesion. Repeated dissection increased the risk of re-do surgery for compressive hematoma [OR=25.1373; 95%CI (0.8468-32.2042); P=0.0347].

Conclusion:

0642 ; IC 95 % (1,5904) ; p = 0,0022]. Aucune des variables de l'étude n'est apparue comme un facteur de risque d'une lésion des nerfs laryngés récurrents. L'évidement ganglionnaire répété augmente le risque d'une révision chirurgicale pour hématome compressif [OR = 25,1373 ; IC 95 % (0,8468-32,2042) ; p = 0,0347].

Conclusion :

La durée de l'intervention, le sexe féminin, l'évidement ganglionnaire répété et une thyroïdectomie totale pour un adénome bénin sont des facteurs de risque à prendre en considération lors de la prise de décision d'une TT en ambulatoire.

I. INTRODUCTION

In light of budgetary requirements imposed on healthcare institutions, developing outpatient surgery is a universal necessity. France is still lagging behind in the development of this type of surgery compared with other OECD (Organisation for Economic Cooperation and Development) countries. To reduce this gap, a multiannual national programme was launched in 2010 by the French Ministry for Health together with Regional Health Agencies (ARS, Agences Régionales de Santé), led by the Directorate General for Healthcare Provision (DGOS, Direction Générale de l'Offre de Soin), to help set a target higher than 50% for outpatient surgery by 2016 [1]. In 2014, outpatient surgery amounted to 44.9% of all surgeries, compared with 37.7% in 2012 [2].

According to the analysis of data from the Medical Information Systems Program (PMSI, Programme de médicalisation des systèmes d'information), 35,367 thyroidectomies were performed in France in 2010, resulting in a cost of several tens of millions of euros reimbursed by national insurance (including 37 million euros to reimburse boxes of levothyroxine and 2.4 million euros for those signed off from work) [START_REF] Hubert | Impact médico-économique et parcours de soins de la chirurgie endocrinienne[END_REF]. One of the potential solutions to decrease these costs is to decrease average length of stay in hospital and to consider eventually introducing outpatient thyroid surgery. Indeed, total thyroidectomy is a surgical procedure that is suitable for outpatient treatment. The procedure is not very painful, causes little bleeding, is not very aggressive from a physiological point of view, is reliable, and does not last long. However, it creates risks of severe complications that could lead to patient death through acute respiratory distress syndrome or irreversible cerebral anoxia in the event of compressive cervical haematoma without emergency evacuation. Furthermore, other non-lethal complications for patients may occur (symptomatic hypocalcaemia or recurrent nerve lesions).

The aim of this study was therefore to establish risk factors for postoperative complications of total thyroidectomy.

II. SUBJECTS AND METHOD

1-Population and study's design

This work is an observational and descriptive study involving patients of the Angers University Hospital (Centre Hospitalier Universitaire d'Angers).

All the adult patients who underwent a total thyroidectomy in our centre between January 2010 and December 2015 were consecutively included in the study.

Patients who underwent an isthmolobectomy, any other partial thyroidectomy (including completion thyroidectomy), or parathyroid surgery were excluded. Patients who had a surgical indication for additional dissection (central neck dissection and/or dissection of the deep cervical lymph chain) were also excluded.

Patient data were collected prospectively by the medical team during patient hospitalisation in our centre using a standard questionnaire and were subsequently entered into a database.

The database was included in the register of the French data protection authority (CNIL, Commission Nationale de l'Informatique et des Libertés) to safeguard the personal data of patients.

2-Variables studied

The different complications studied included: recurrent nerve lesions, immediate postoperative hypoparathyroidism, and the occurrence of postoperative bleeding. They were defined, respectively, by: the presence of bilateral or unilateral paralysis of the vocal cords linked to postoperative dysphonia and shown using nasofibroscopy performed by a specialised physician on D1; symptomatic (2.00 mmol/L < Ca++ < 2.20 mmol/L) or asymptomatic (Ca++ < 2.00mmol/L) hypocalcaemia in the first 3 postoperative days requiring calcium plus vitamin D supplementation; and the formation of a haematoma in the thyroid bed requiring further surgery in the operating room.

Calcium plus vitamin D supplementation could be administered in various ways: calcium intravenous injection, calcium per os, and alfacalcidol per os, either alone or in combination with calcium per os.

The nasofibroscopy was not routinely performed; it was only done in case of postoperative dysphonia.

The variables studied as potential risk factors were: age, sex (male or female), obesity (BMI>30), the surgeon's experience (number of total thyroidectomies performed during career), antiplatelet and/or anticoagulation treatment, surgery duration (in minutes), recurrent dissection, an operated thyroid disorder, intraoperative search for recurrent nerves, and past surgery and/or cervical radiation therapy.

The anatomopathological analysis of the sample following surgical excision determined the disorder operated on (multinodular goitre (MNG), Graves' disease, lymphocytic thyroiditis, benign adenoma, cancer). The study's primary endpoint was the appearance of a recurrent nerve lesions, the need for postoperative calcium plus vitamin D supplementation, and/or further surgery for haematoma.

3-Surgical techniques

Trained surgeons performed the thyroidectomies, via anterior cervicotomy only.

Classic dissection techniques were used. Haemostasis techniques included ligatures; vascular clips; sutures; monopolar, bipolar, or ultrasonic electrocoagulation; or a combination of several techniques.

When the preoperative assessment recommended it, recurrent lymph node dissection was performed during the same surgery.

Drainage of the thyroid bed was not done systematically and was left to the surgeon's discretion based on intraoperative observations. None of the surgeries were performed using neurostimulation of the recurrent laryngeal nerves.

4-Statistical analysis

Data were described in a conventional way in the descriptive analysis, as mean ± standard deviation for Gaussian quantitative variables and as median (95CI) for the other quantitative variables, and as n (%) for qualitative variables.

As part of the descriptive analysis, Fisher's exact test, Student's t-test or the Mann-Witney U test were performed, depending on the context. We also performed multivariate logistic regressions to explain our binary variables. A manual backward selection was performed for the selection of explanatory variables to be included in the model. The variables age, sex, obesity (BMI>30) and surgery duration were forced into each model. The odds ratio (OR) derived from the logistic regression are presented with the 95% confidence intervals (95CI).

Statistical analysis was performed using R Statistical Software.

III. RESULTS

1-Population characteristics

Four hundred and twenty-four patients who underwent total thyroidectomy between January 2010 and December 2015 were included in our study.

The population flow diagram can be seen in Figure 1.

The median age of our cohort was 51 years [95CI (49.5-52.5)] and most patients were female (77.65%).

All the demographic and clinical characteristics of the population are summarised in Table 1.

Eighty-five patients (20.04%) presented symptomatic and/or substituted hypocalcaemia and required calcium plus vitamin D supplementation, 18 patients (4.25%) presented a recurrent lesion shown by nasofibroscopy, and 4 patients (0.94%) required reoperation for compressive haematoma.

The overall premature morbidity observed in our study was 24.06%.

The distribution of complications in univariate analysis is summarised in Table 2.

2-Postoperative hypocalcaemia

In multivariate analysis, female patients were more likely to present symptomatic and/or substituted hypocalcaemia [OR=3.2584 95CI(1.5500-7.7515), p=0.0036].

Furthermore, the longer the surgery duration, the higher the risk of postoperative hypocalcaemia [OR=1.0095 95CI(1.0020-1.0172), p=0.0129]. Finally, the final diagnosis was also linked to the likelihood of receiving calcium plus vitamin D supplementation. Indeed, patients who were diagnosed with MNG, Graves' disease, lymphocytic thyroiditis or cancer were all less likely to develop a postoperative hypocalcaemia than those who were diagnosed with a benign adenoma [OR=5.0642 95CI(1.7768-14.5904), p=0.0022]. All the results are summarised in Table 3.

An analysis of the benign adenoma sub-group was performed to try to determine whether the size of the adenoma could explain the result's significance. Assuming a non-normal distribution, a Mann-Witney U test was performed to compare medians.

There is no significant difference in the medians of adenoma sizes in the groups "with hypocalcaemia" and "without hypocalcaemia". Results are presented in Table 4.

3-Recurrent laryngeal nerve lesions

No independent risk factor was found in multivariate analysis. Results are presented in Table 5.

4-Compressive haematoma

One variable stands out in multivariate analysis. Patients having undergone recurrent lymph node dissection were more likely to require further surgery for compressive haematoma compared with patients who did not [OR=25.1373 95CI(0.8468-32.2042), p=0.0347]. Results are presented in Table 6.

IV. DISCUSSION

Patients principally undergo total thyroidectomies for multinodular goiter (with or without thyroid dysfunction) or Grave's disease for which only total thyroidectomy is recommended [START_REF] Corvilain | Treatment of adult Graves' disease[END_REF]. It remains a high-risk surgery. Although decreasing, its morbidity rate (20% to 30% all complications combined) [START_REF] Menegaux | Thyroïdectomie ambulatoire : recommandations de l'Association francophone de chirurgie endocrinienne (AFCE). Enquête sur les pratiques actuelles[END_REF] makes surgeons reluctant to perform the procedure on an outpatient basis. In an American study, Charles T. Tuggle at al. showed that even in specialised centres with many patients, outpatient procedures remain rare and are performed on a small number of carefully selected patients [START_REF] Tuggle | Same-Day Thyroidectomy: A Review of Practice Patterns and Outcomes for 1,168 Procedures in New York State[END_REF].

Several learned institutions have published recommendations relating to outpatient management of total thyroidectomies (TT). The American Thyroid Association indicates that the surgery can be performed on an outpatient basis for carefully selected patients and insists on informing the latter about the potential risks, but does not recommend outpatient treatment [START_REF] Terris | American Thyroid Association Statement on Outpatient Thyroidectomy[END_REF]. In 2013, the French Association of Endocrine Surgery (AFCE, Association Francophone de Chirurgie Endocrinienne) made recommendations to that effect (grade C) [START_REF] Menegaux | Thyroïdectomie ambulatoire : recommandations de l'Association francophone de chirurgie endocrinienne (AFCE). Enquête sur les pratiques actuelles[END_REF], recommending 24-hour hospitalisation (1 night) for TT patients.

The association also indicated that the surgery could be performed on an outpatient basis in the case of carefully selected, well-informed patients and insisted on the surgeon's responsibility in making this decision.

There are many relative contraindications (CIs) and exclusion criteria for TT on an outpatient basis, including those relating to the patient and his or her disorder as well as a number of psychological and social factors: [START_REF] Menegaux | Thyroïdectomie ambulatoire : recommandations de l'Association francophone de chirurgie endocrinienne (AFCE). Enquête sur les pratiques actuelles[END_REF] Several studies have suggested that some of these contraindications could be lifted. They argue, for example, that anticoagulation treatment (and antiplatelet treatment) is not a contraindication as long as the haemostasis is performed carefully [START_REF] Christou | Complications after total thyroidectomy[END_REF]. Furthermore, being aged over 50 years seems to be protective factor against postoperative hypocalcaemia [START_REF] Huang | The preoperative evaluation prevent the postoperative complications of thyroidectomy[END_REF], while J.B. Finel et al. have shown that a BMI over 25 does not seem to be a risk factor for postoperative complications [START_REF] Finel | Thyroidectomy in patients with a high BMI: a safe surgery[END_REF].

There is a lack of consensus relating to the treatment of postoperative hypocalcaemia and its incidence varies depending on the definition it is given. It is temporary in 20 to 30% of cases, and permanent in 1 to 4% of cases [START_REF] Tomusch | Multivariate analysis of risk factors for post-operative complications in benign goiter surgery : prospective multicenter study in Germany[END_REF]. In our study, patients with minor and symptomatic postoperative hypocalcaemia (calcaemia corrected between 2 and 2.20 mmol/L), as well as those with major hypocalcaemia with or without clinical signs (calcaemia corrected < 2 mmol/L), received calcium plus vitamin D supplementation. The postoperative hypocalcaemia rate was 20.04%. We were able to demonstrate that female gender was an independent risk factor for postoperative hypoparathyroidism, which confirms the results of the study by Duclos et al. (BMJ, 2012) [START_REF] Duclos | Influence of experience on performance of individual surgeons in thyroid surgery : prospective cross sectional multicentre study[END_REF]. The same is true for surgery duration: the longer it is, the higher the risk of postoperative hypocalcaemia. Surgery duration can be linked to the surgeon's experience. Indeed, a trained surgeon decreases the risk of parathyroid gland lesions, while 5 to 19 years of experience guarantees the lowest complication rate [START_REF] Duclos | Influence of experience on performance of individual surgeons in thyroid surgery : prospective cross sectional multicentre study[END_REF]. Surprisingly, our study showed that patients who underwent surgery for benign adenoma were more at risk of developing postoperative hypocalcaemia than patients who underwent surgery for MNG, cancer, lymphocytic thyroiditis or Graves' disease.

The size of the adenoma did not seem to explain this phenomenon (Table 4). After rereading anatomopathological reports of total thyroidectomy samples, we were able to demonstrate a higher incidence of incidental parathyroidectomies (IP) in the group of patients who underwent surgery for a benign adenoma and who presented postoperative hypocalcaemia. This most likely explains our results, especially knowing that IPs are significantly linked to a higher risk of symptomatic hypocalcaemia 2 weeks after the surgery, as well as the risk of premature postoperative biochemical hypocalcaemia [START_REF] Applewhite | Incidence, Risk Factors, and Clinical Outcomes of Incidental Parathyroidectomy During Thyroid Surgery[END_REF].

There is a lack of consensus on the ways to predict the occurrence of postoperative hypoparathyroidism despite the fact that many studies have already addressed the topic by trying to determine whether the calcium or PTH rate could be a predictive marker. Notably, Nahas et al. were able to show that an increased calcium levels between the 6 th and 12 th hour following surgery had a 100% positive value for predicting a return to normal calcium levels [START_REF] Nahas | A safe and cost-effective short hospital stay protocol to identify patients at low risk for the development of significant hypocalcemia after total thyroidectomy[END_REF]. Nevertheless, with PTH reaching its lowest level at the 3 rd postoperative hour (contrarily to the calcium rate, which is at its lowest on the 3 rd day), it seems to be a more effective marker within the framework of outpatient treatment [START_REF] Hermann | Kinetics of serum parathyroid hormone during and after thyroid surgery[END_REF]. More so than the PTH rate, its decrease seems to provide a strong argument for postoperative hypocalcaemia. According to a meta-analysis performed in 2007 by Noordzij et al., if the PTH rate decreases by 65% compared with its basal rate in the 6 th postoperative hour, it is predictive of hypocalcaemia with Se = 96.4% and Sp = 91.4% [START_REF] Noordzij | Early Prediction of Hypocalcemia after Thyroidectomy using Parathyroid Hormone: An Analysis of Pooled Individual Patient Data from Nine Observational Studies[END_REF]. A routine PTH assay in all centres performing total thyroidectomies therefore seems beneficial for the treatment of patients on an outpatient basis.

Recurrent paralysis contributes to thyroid surgery morbidity and to a deterioration of the patient's quality of life. According to a meta-analysis involving 27 studies, published in 2009, recurrent paralysis affects 9.8% of patients on average when it is temporary and 2.3% of patients on average when it is permanent [START_REF] Jeannon | Diagnosis Of recurrent laryngeal nerve palsy after thyroidectomy : a systematic review[END_REF]. In our study, 18 patients were affected by postoperative dysphonia, which revealed vocal cord paralysis (4.25%). A single case of bilateral paralysis (Table 1) in abduction was observed, but it was not life-threatening for the patient and was treated by vocal cord medialisation through reinjection of autologous fat, following the failure of speech and language therapy. We did not find any independent risk factors or protective factors during our study. We were able to determine that visualising the recurrent nerve is not a risk factor for recurrent nerve lesions. In fact, this is in line with recommendations, which call for the need to visualise systematically, during surgery, the 2 recurrent nerves [START_REF] Chandrasekhar | Clinical practice guideline: improving voice outcomes after thyroid surgery[END_REF]. Hermann et al. have shown that visualising the recurrent nerve reduces the risk of intraoperative damage by 50% [START_REF] Hermann | Laryngeal Recurrent Nerve Injury in Surgery for Benign Thyroid Diseases. Effect of Nerve Dissection and Impact of Individual Surgeon in More Than 27,000 Nerves at Risk[END_REF].

Compressive haematoma remains the complication most feared by surgeons because it is potentially life-threatening if emergency evacuation cannot be performed. However, it is also rare, with an estimated rate between 0.2 and 2.7% [START_REF] Christou | Prise en charge des complications de la thyroïdectomie[END_REF]. The first warning sign is acute dyspnoea. Our study found a 0.94% rate of compressive haematoma that required surgical evacuation in the operating room, without any association with excess mortality. Despite the small number of haemorrhages found in our study, we were able to demonstrate that recurrent dissection was an independent risk factor of compressive haematoma. To the best of our knowledge, this is an unprecedented result. Other risk factors were found, such as pre-existing dyspnoea at the time of surgery and male gender in a retrospective study on a series of 6,830 patients with 70 compressive haematomas [START_REF] Leyre | Does the risk of compressive hematoma after thyroidectomy authorize 1-day surgery?[END_REF], as well as an advanced age of the patient and the surgeon's lack of experience [START_REF] Promberger | Risk factors for postoperative bleeding after thyroid surgery[END_REF]. In our study, drainage of the thyroid bed was left to the surgeon's discretion based on intraoperative observations, and it is therefore not included in the final results. However, it does not seem to be a protective factor for haemorrhages and seems rather to increase the risk of infection [31]. Moreover, a meta-analysis of the Cochrane Library has shown its futility in routine thyroidectomies [START_REF] Samraj | Wound drains following thyroid surgery[END_REF].

There are several limitations to this study. First of all, our rate of recurrent nerve paralysis may be underestimated. Indeed, we did not perform a nasofibroscopy systematically but only in case of dysphonia. Thus some of the paralysies which were not associated with postoperative dysphonia were not taken into account. Secondly, although our data were collected prospectively, we did not show the rate of definitive hypocalcaemia. Our goal was to assess criteria for outpatient management for total thyroidectomy and the rate of immediate postoperative hypocalcaemia seemed more appropriate in such a decision. Some authors consider definitive hypocalcaemia as the only true complication of total thyroidectomy, but immediate postoperative hypocalcaemia, even transient, may compromise outpatient thyroidectomy according to its severity.

In regard of surgery's evolution and the way in which it is approached by the health authorities, outpatient surgery will more and more prevail for physicians. As clinicians, it will be our responsibility to decide which actions are eligible for such management, and if thyroidectomies are to find their place in it, this would not be done without careful attention to the selection of patients and the implementation of validated and consensual protocols to allow an acceptable surgery with minimal risk for patients.

According to our study, surgery duration, female gender, recurrent dissection, and benign adenoma seem to be factors that should be considered when making decisions regarding the potential performance of a total thyroidectomy on an outpatient basis.

  [START_REF] Spanknebel | Thyroidectomy using local anesthesia: a report of 1,025 cases over 16 years[END_REF][START_REF] Terris | Outpatient thyroid surgery is safe and desirable[END_REF][START_REF] Spanknebel | Thyroidectomy using monitored local or conventional general anesthesia: an analysis of outpatient surgery, outcome and cost in 1,194 consecutive cases[END_REF][START_REF] Sahai | Short-stay thyroid surgery[END_REF][START_REF] Materazzi | One-day thyroid surgery: retrospective analysis of safety and patient satisfaction on a consecutive series of 1,571 cases over a three-year period[END_REF][START_REF] Teoh | Feasibility study of day case thyroidectomy[END_REF][START_REF] Chin | Ambulatory thyroid surgery: an audit of safety and outcomes[END_REF][START_REF] Mowschenson | Outpatient thyroid and parathyroid surgery: a prospective study of feasibility, safety, and costs[END_REF] -Obesity (BMI > 30kg/m²),-Antiplatelet and/or anticoagulation treatment, -Age over 50 years, -Certain thyroid disorders (lateral dissection for suspicion of lymph node metastases, Graves' disease, extensive resection for a locally advanced malignant disorder, iterative surgery), -The surgeon's lack of experience, -Male gender, -A plunging goitre or excision volume > 80mL -Lack of sufficient knowledge of the language, -The patient's lack of motivation.

Figure

  Figure 1. Population flow diagram

Table 1 . Demographic and clinical characteristics of the 424 patients included, Department of Digestive and Endocrine Surgery, Angers University Hospital

 1

	Patients
	n=424 (%)

Table 2 . Distribution of complications. Descriptive analysis (Fisher's exact test)

 2

	* p<0.05; **p<0.01; ***p<0.001. p-value significant (i.e., <.05) indicated in bold.
	TT: total thyroidectomies

Table 3 . Risk factors for postoperative hypocalcaemia. Multivariate analysis.

 3

		Postoperative hypocalcaemia
		OR (95%IC)	p
	Female gender	3.2584 (1.5500-7.7515)	0.0036 **
	Age	0.990.9 (0.9729-1.0090)	0.3210
	Obesity (BMI>30)	0.05593 (0.2978-1.0044)	0.0597
	Surgery duration	1.0095 (1.0020-1.0172)	0.0129 *
	Benign adenoma	5.0642 (1.7768-14.5904)	0.0022 **
	* p<0.05; **p<0.01; ***p<0.001. p-value significant (i.e., <.05) indicated in bold.

Table 4 . Size of benign adenomas. Comparison of medians. Mann-Witney U test.

 4

	Benign adenoma with	Benign adenoma	P value
	postoperative	without hypocalcaemia
	hypocalcaemia	n=9 (50%)
	n=9 (50%)
	Adenoma size in cm	1.7	2.5	0.9283
	(median)

Conflicts of interest:

The authors declare to have no conflicts of interest.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.


Xavier Dieu
email: xavierdieu@chu-angers.fr

Guillaume Sueur

Valérie Moal

Florence Boux De Casson

Nathalie Bouzamondo

Natacha Bouhours

Claire Briet

Frédéric Illouz

Pascal Reynier

Régis Coutant

) Frédéric Illouz

Patrice Rodien

Delphine Mirebeau-Prunier

Apparent resistance to thyroid hormones: From biological interference to genetics

Keywords: resistance to thyroid hormones, immunoassay interference, THRB, transthyretin, albumin, TBG résistance aux hormones thyroïdiennes, interférence analytique, THRB, transthyrétine, albumine, TBG

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

First described by Refetoff et al in 1967 [START_REF] Refetoff | Familial syndrome combining deaf-mutism, stuppled epiphyses, goiter and abnormally high PBI: possible target organ refractoriness to thyroid hormone[END_REF], the resistance to thyroid hormone syndrome (RTH) is a rare disease (1 case in every 50,000 births). Clinical manifestations are variated. The most frequent are a goiter (85%), tachycardia (75%) and attention deficit hyperactivity disorder (70% of children). These non-specific symptoms may lead to thyroid hormone assessment and to the detection of dissociated results for TFT (thyroid function test i.e. increase in thyroid hormone (TH) and a normal or mildly elevated concentration of TSH).

In 1989, the phenotype was related to mutations in the gene THRB coding for thyroid receptor β (TRβ). Indeed, thyroid hormones exert their biological actions via two types of thyroid receptor: TRβ and TRα. Their distribution and expression level vary among tissues [START_REF] Vella | The actions of thyroid hormone signaling in the nucleus[END_REF]. TRβ is expressed in the hypothalamus and pituitary gland where it conveys the TH negative feedback on TSH secretion. In case of an inactive TRβ caused by a pathogenic variant in THRB, the TH concentration needed in order to regulate the TSH secretion is higher than in normal individuals. This explains the biological phenotype: high levels of T4 and T3, and unsuppressed TSH. Moreover, the high levels of T4 and T3 explain the clinical manifestation of the RTH, through TH action mediated by functional TRα especially in heart, gut and autonomous nervous system.

Other genes with modified TH action are involved in the discrepancy between TH and TSH concentrations [START_REF] Dumitrescu | The syndromes of reduced sensitivity to thyroid hormone[END_REF]. We can find genes coding for thyroid receptor α (THRA) [START_REF] Vlaeminck-Guillem | TRα receptor mutations extend the spectrum of syndromes of reduced sensitivity to thyroid hormone[END_REF], for the protein involved in insertion of selenocystein in deiodinases (SECISBP2) [START_REF] Dumitrescu | Mutations in SECISBP2 result in abnormal thyroid hormone metabolism[END_REF], and for the hormone cell membrane transporter MCT8 (SLC16A2) [START_REF] Dumitrescu | A novel syndrome combining thyroid and neurological abnormalities is associated with mutations in a monocarboxylate transporter gene[END_REF]. Thyrotropic pituitary adenoma may produce the same hormonal phenotype. The diagnosis will be confirmed by the identification of a pituitary tumor via MRI. However the most frequent differential diagnosis of RTH are assay artefacts. Assessment of TH and TSH concentration mainly relies on immunoanalysis techniques. The TH circulating in the blood is mainly bound to proteins, whereas a very small fraction (0.02% and 0.3 % for T4 and T3, respectively) is free [START_REF] Pappa | Inherited defects of thyroxine-binding proteins[END_REF]. The three main binding proteins are albumin, transthyretin (TTR) and thyroxin-binding globulin (TBG). These proteins bind T3 and T4 in different proportions. The assessment of free T4 (fT4) and free T3 (fT3) by immunoanalysis techniques may therefore be influenced by various factors. It is essential to note that the impact of these factors is directly related to the type of immunoanalysis platforms used [START_REF] Sapin | Interférences dans les immunodosages : mécanismes et conséquences en endocrinologie[END_REF][START_REF] Favresse | Interferences With Thyroid Function Immunoassays: Clinical Implications and Detection Algorithm[END_REF]. Main types of interference in TFT are biotin, and antibodies (antistreptavidin antibodies, antirhutenium TH antibodies and heterophilic antibodies) [START_REF] Li | Association of Biotin Ingestion With Performance of Hormone and Nonhormone Assays in Healthy Adults[END_REF][START_REF] Lim | Biotin interferes with free thyroid hormone and thyroglobulin, but not TSH measurements using Beckman-Access immunoassays[END_REF][START_REF] Raverot | Letter to the editor: A case of laboratory-generated "thyroid dysfunction[END_REF]. Other factors may affect by the equilibrium between free and bound TH, such as heparin, non-steroidal anti-inflammatory drugs, antibodies as well as quantitative and qualitative changes in the binding proteins [START_REF] Favresse | Interferences With Thyroid Function Immunoassays: Clinical Implications and Detection Algorithm[END_REF] . The latter constitute the field of this study. Genetic variants affecting the affinity of these three TH transport proteins (Albumine, TTR, TBG) for the TH have been reported. The most frequent involve albumin, leading to familial hyperthyroxinemic dysalbuminemia, with a prevalence of 0.01 to 1.8 %, depending on the population studied. Mutations are located in the T4 binding site (codon 218 and 221) and enhance affinity [START_REF] Kragh-Hansen | Human serum albumin isoforms: genetic and molecular aspects and functional consequences[END_REF]. The transthyretin variants are sorted into amyloidogenic and nonamyloidogenic. The most frequent variant involves codon 109 and is non-amyloidogenic [START_REF] Pappa | Inherited defects of thyroxine-binding proteins[END_REF]. The TBG variants lead to partial or total deficit of the protein and to low total TH concentration whereas the free TH concentration is usually normal [START_REF] Pappa | A Novel Mutation in the TBG Gene Producing Partial Thyroxine-Binding Globulin Deficiency (Glencoe) Identified in 2 Families[END_REF]. In all these situations, the change of affinity for TH modifies the equilibrium between free and bound hormones in the immunoassay. These variants have no thyroid-related clinical consequence for the patient, but identifying these artefacts is of importance to avoid unnecessary therapeutics.

Our Reference Centre for Rare Diseases of Thyroid and Hormone Receptors, receives around 50 samples each year for THRB sequencing because of dissociated thyroid function tests (TFT). Only a quarter of these cases exhibit a mutation of THRB. We therefore tried to explain the very high proportion of cases with no mutation despite a suspicion of RTH syndrome based on discordant TFT.

Patients and Methods

Patients

Fifty-eight patients (22 male and 36 female), investigated during year 2017 for suspicion of RTH syndrome, were included in the study. All patients came from several regions of France. All had either free T4 (fT4) and / or free T3 (fT3) concentration above the upper limit of the normal range of the assay used in their routine laboratory with normal or elevated TSH concentration. Clinical data were collected from referring doctor of patients. Cardiac signs were defined by a supraventricular arrythmia (flutter or fibrillation), a sinusal tachycardia, other conduction abnormalities or a cardiac failure. The hyperactivity, agitation or attention deficit were reported by the patient or his family. Ultrasonography of thyroid was performed to detect goiter or thyroid nodules.

Genetic analysis

All patients signed an informed consent form for genetic testing. DNA was extracted from all blood samples with an EZ1 extraction kit (Qiagen, Hilden Germany). High throughput sequencing of the THRB, ALB, TTR, SERPINA7, THRA, SLC16A2, and SECISBP2 genes were performed on an Ion proton sequencer (Thermofischer scientific, Waltham, USA).

Thyroid function tests

The first thyroid function tests were performed in different laboratories. Information on technique, assay used and normal ranges were available for 46/58 patients. Secondarily, we repeated fT4 and fT3 analyses with another assay in our laboratory on a Siemens ADVIA Centaur for 49 plasma samples.

Normal ranges were for fT4: 9-19 pmol/L and for fT3: 2.6-5.7 pmol/L).

Statistics

Statistical analysis was performed with XLSTAT® and BiostaTGV. A Mann Whitney test was used for quantitative data and a Fischer Exact Test for clinical qualitative data. Results were expressed as median +/-Standard Deviation for age. Plots were made using Microsoft Excel or using Plotly (through its Python API).

Results

Genetic analysis

Genetic analysis was performed for the 58 samples [FIGURE 1]. A pathogenic variant with loss of function in THRB was found in 15/58 cases (26%) confirming the diagnosis of RTH. Variants were found in genes coding for TH serum transport proteins in 14 cases, 8 in ALB (13.8%) and 6 in TTR (10.3%) and 0 in SERPINA7. No pathogenic variant was identified in THRA, SECISBP2, SLC16A2.

Thyroid function test verification

We quantified fT3 and fT4 for 49 samples with the same immunoassay (Siemens ADVIA Centaur)

[TABLE 1].
Out of 10 plasma samples available from 15 patients with a THRB mutation, 9 displayed both an elevated fT4 and fT3 concentration, while only one displayed an isolated increase fT3. There was no difference in the extent of increase between the different pathogenic variants.

Thirteen out of 14 plasma samples taken from patients with genetic variant of TH serum transport proteins could be assessed. For the 8 patients with albumin variant, 3 had normal fT4 and fT3 concentration, 3 had both elevated fT4 and fT3, 2 had an increase in fT4 and none had an increase in fT3 alone. For the 6 patients with TTR variant, 2 had normal fT4 and fT3 concentration, none had both elevated fT4 and fT3, 1 had an increase in fT4 and two had an increase in fT3 alone.

Twenty-six samples were available for 29 patients without any genetic variant identified. In 15 out of 26, normal fT4 and fT3 were found, which suggests an analytical interference in the assay initially used in the referring centre. In 11 samples, a discrepancy between TH and TSH values was confirmed with both elevated fT4 and fT3 for 5 samples, an increase in fT4 alone for 3 samples and an increase in fT3 alone for 3 samples.

Clinical Information

We subdivided the patients into 3 groups: the first group, a RTH group (N=15) of patients with a pathogenic variant of THRB; the second group, an Analytical interference group (N= 29) of patients with genetic variants of TH serum transport proteins and patients with a normal biological assay with a second analytical technique; and the third group, an unexplained discrepancy group (N=14) of patients with abnormal biological assay (fT3, fT4) even using two different techniques or patients with no second hormonal assay.

The mean age of patients was 36 years (19 months to 78 years). The patients in unexplained discrepancy group were older than patients in RTH group (50+/-22 versus 29 +/-16, p= 0.011) or analytical interference group (30 +/-22, p= 0.072). Sixty percent (9/15) of patients in RTH group were diagnosed before the age of 30 and 100% before the age of 60. Twenty-nine percent (4/14) of patients in unexplained discrepancy group were diagnosed before the age of 30 and 36 % (5/14) after the age of 60. An analytical interference was identified more often in women (19/29) after the age of 30 in 63% (12/19) of them. At the opposite an analytical interference were rarer in men (10/29) and was found in 80% (8/10) of them before 30. A fisher exact test showed that this result was statistically significant with a p-value of 0.050 [FIGURE 2].

Clinical data were available in 83% of patients (48/58). These clinical informations revealed that the findings of discrepant thyroid functional testing were fortuitous in 50% of analytical interference, in 20% of RTH and 15% of unexplained discrepancy (p= 0.072) [FIGURE 3B].

Cardiac symptoms and hyperactivity were identical and not statistically different between three groups of patients. Cardiac symptoms, tachycardia or atrial fibrillation, were reported in 30% of patients in the RTH group, 35% in the analytical interference group and 38% in the unexplained discrepancy group. Hyperactivity reported by the patient or his family was found in 10% of the RTH patients, 15% in the analytical interference group and 23% in the unexplained discrepancy group.

A non-significant trend for a lower prevalence of goiter was observed in the analytical interference group, lower than both the confirmed RTH group and the unexplained discrepancy group: 15% versus 40% and 38%, respectively (p=0.149).

Discussion

We report the biological findings from 58 suspected cases of RTH submitted to the Reference Centre for Rare Diseases of Thyroid and Hormone Receptors during 2017. Fifteen mutations of THRB were identified, confirming the suspected diagnosis, along with 14 variants of TH serum proteins transport (ALB and TTR) producing analytical interferences. The quantification of fT3 and fT4 using another technique than the initial one confirmed increased fT4 and/or fT3 in 100% cases of RTH, in 61% of patients with TH protein transport variants and in 42% of unexplained discrepancies.

In our series, at first glance, only 26% of suspected cases of RTH are confirmed, which may appear very low compared to the literature [START_REF] Dumitrescu | The syndromes of reduced sensitivity to thyroid hormone[END_REF]. When we looked for other genes which may produce a discrepancy in thyroid test with various mechanisms, we found no other genetic defects that reduce the TH biological activity.

We therefore looked for artefacts that may produce the same discrepancy in a thyroid test. Since biological interferences are numerous and vary between different assays, we measured TH again in an assay different from the initial one. Alternatively normal and abnormal results for the same patients, depending of the method used, strongly suggest a technique-related artefact [START_REF] García-González | Serum sample containing endogenous antibodies interfering with multiple hormone immunoassays. Laboratory strategies to detect interference[END_REF][START_REF] Sapin | Thyroxine (T4) and tri-iodothyronine (T3) determinations: techniques and value in the assessment of thyroid function[END_REF]. The reference technique associating equilibrium dialysis with subsequent TH assay in mass spectrometry is rarely used as it is technically demanding [START_REF] Van Houcke | IFCC international conventional reference procedure for the measurement of free thyroxine in serum: International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Working Group for Standardization of Thyroid Function Tests (WG-STFT)(1)[END_REF]. The verification of fT3 and fT4 was performed on a Siemens Advia Centaur automate. This immunoassay does not suppress all the interferences and can also be disturbed by artefacts. Nevertheless, the simple verification in a different assay allows for the apparent normalisation of the thyroid test, which suggests the presence of interferences, in 26% of cases.

Among possible causes of erroneous thyroid test, the presence of anti-T4 or anti-T3 antibodies, Heterophilic antibodies (HAMA), anti-avidin antibodies are well known, not forgetting the biotin interference in streptavidine-biotin based assays. However, genetic variants modifying the affinity of serum transport proteins for TH may also disturb the equilibrium between free and bound hormones and impair the performance of free hormone assays. Here we found variants of albumin and transthyretin in 24% of cases. It should be stressed that this is as frequent as mutations of THRB in this specific population. Noteworthy, the analytical interferences due to serum transport protein variants are assay-specific, as was previously mentioned for familial dysalbuminemic hyperthyroxinemia [START_REF] Kragh-Hansen | Clinical, Genetic, and Protein Structural Aspects of Familial Dysalbuminemic Hyperthyroxinemia and Hypertriiodothyroninemia[END_REF][START_REF] Cartwright | Familial dysalbuminemic hyperthyroxinemia: a persistent diagnostic challenge[END_REF]. This study allowed us to reduce the group of true unexplained discrepant thyroid test, i.e. absence of mutation of THRB, or transport protein and supposed analytical interference to 24% of cases. This is in agreement with the reported frequency (15%) of RTH with no THRB mutation. Also, we confirm that in patients with high fT4 and fT3 and non-suppressed TSH, in absence of mutation of THRB there is very little chance of finding a mutation in the other genes involved in syndromes of reduced sensitivity to thyroid hormone, up to now. Therefore, to avoid unreliable diagnoses, initially ruling out analytical interferences by simply repeating the thyroid test in different assays is mandatory. Genetic analysis of THRB, and TH serum transport proteins, should then be performed. Ultimately, other genes of the thyroid hormone signalling pathway could be analysed although we did not find any pathogenic variant in the latter.

Although new generation sequencing techniques allow for an easy sequencing of many genes in the same run, they should not substitute a cautious step by step analysis of cases.

Figure 3 :

 3 Figure 3 : Detail of the different clinical symptoms (A) and distribution of main clinical symptoms (%) (B) according to the etiology of TSH/TH discrepancy. RTH: Resistance to thyroid hormones due to a variant of the THRB gene, TH: thyroid hormones

Table 1 :

 1 Quantification of ft4 and fT3 realised on a Siemens ADVIA Centaur according to the etiology of the TSH/TH discrepancy. Etiology of the TSH/TH discrepancy according to the presence or absence of genetic variant for 58 samples sent in 2017 to the University Hospital of Angers. Sequencing of THRB (Thyroid Hormone Receptor β), THRA (Thyroid Hormone Receptor α), SLC16A2 (Solute Carrier Family 16 Member 2), SECISBP2 (Selenocysteine insertion sequence binding protein 2), ALB (Albumin), TTR (Transthyretin) ) and SERPINA7 (thyroxin binding globulin (TBG)) was performed for the 58 samples. fT4 and fT3 quantification was performed on samples at the University hospital of Angers on a Siemens ADVIA Centaur.

		Genetic variants
					No genetic variant
		(N=29)
		THRB (N=15) ALB (N=8) TTR (N=6)	(N=29)
	fT4 Nl fT3 Nl	0	3	2	15
	fT4 ↗ fT3 ↗	9	3	0	5
	fT4 ↗ fT3 Nl	0	2	1	3
	fT4 Nl fT3 ↗	1	0	2	3
	No data	5	0	1	3
	Nl : Quantification within the limits of normality (fT4: 9-19pmol / l; fT3: 2.6-5.7pmol / l)
	↗ : Quantification superior to the upper limit of normality.
	N: Sample number

RTH: Resistance to thyroid hormones due to a variant of the THRB gene, TH: thyroid hormones

FUNDING

Grant from Angers University Hospital and National Research Agency THYROMUT

Conflict of Interest: none declared