Neurosurg Rev DOI 10.1007/s10143-014-0553-7

ORIGINAL ARTICLE

Transoral robotic-assisted skull base surgery to approach the sella turcica: cadaveric study Dorian Chauvet & Antoine Missistrano & Mikaël Hivelin & Alexandre Carpentier & Philippe Cornu & Stéphane Hans

Received: 27 August 2013 / Revised: 27 January 2014 / Accepted: 23 March 2014 # Springer-Verlag Berlin Heidelberg 2014

Abstract Transoral robotic surgery (TORS) offers new possibilities that have not been experimented in the field of minimally invasive skull base neurosurgery. We propose to evaluate the feasibility of transoral approach to the sella turcica with the da Vinci system on cadavers. We performed four robot-assisted dissections on human fresh cadavers in order to reach the pituitary fossa by the oral cavity. Cavum mucosa dissection was performed by the head and neck surgeon at the console and then the sphenoid was drilled by the neurosurgeon at the bedside, with intraoperative fluoroscopy and a “double surgeon” control. Mucosa closure was attempted with robotic arms. We succeeded in performing a sellar opening in all cadavers with a minimally invasive approach, as the hard palate was never drilled. The video endoscope offered a large view inside the sphenoidal sinus, as observed in transnasal endoscopy, but with 3D visualization. The camera arm could be inserted into the sphenoidal sinus, and instrument arms in the pituitary fossa. Operative time to reach the pituitary fossa was approximately 60 min in all procedures: 20 min of initial setup, 10 min of mucosal dissection, and 30 min of sphenoid surgery. New anatomical landmarks were defined. Advantages and pitfalls of such an D. Chauvet (*) : A. Carpentier : P. Cornu Department of Neurosurgery, Groupe Hospitalier Pitié-Salpêtrière, 43-87 Boulevard de l’Hopital, 75013 Paris, France e-mail: [email protected] A. Missistrano Intuitive Surgical, Sunnyvale, CA, USA M. Hivelin Department of Plastic Surgery, Hopital Européen Georges Pompidou, Paris, France S. Hans Department of Head and Neck Surgery, Hopital Européen Georges Pompidou, Paris, France

unpublished technique were discussed. This is the first cadaveric study reported da Vinci robotic transoral approach to the sella turcica with a minimally invasive procedure. This innovative technique may modify the usual pituitary adenoma removal as the sella is approached infero-superiorly. Keywords Transsphenoidal surgery . Minimally invasive surgery . Transoral approach . Robotic-assisted surgery

Introduction Transsphenoidal surgery has been initially described in the early 1900s by pioneers of neurosurgery, such as Halstead or Cushing [23]. Then, this procedure has been diffused by Dott [4], Guiot [7], and finally Hardy [13]. Over the past 30 years, endoscopic transnasal techniques have gained a major interest, and anatomic limits have been widened in order to extend neurosurgical applications [16, 18, 19, 28]. Unfortunately, these endoscopic approaches continue to present several disadvantages, the main one remaining the postoperative cerebrospinal liquid leak [17, 26]. Other inconveniences can be depicted, such as the 2D vision, the narrowness of the operative corridor, the necessity to remove occasionally some endonasal structures, as turbinates or nasal septum, the ergonomic discomfort for the surgeon to perform fine dissection with his two hands, the impossibility to suture, and the quite long learning curve. For many years, robotic-assisted surgery using the da Vinci system (Intuitive Surgical Inc, Sunnyvale, CA, USA) has been greatly developed, especially in urology [31] and gynecology [1]. This innovative device offers 3D visualization, motion scaling, tremor filtration, and an increase freedom of movement within narrow spaces [2]. Recently, robotic-assisted surgery has been performed for pharyngeal and laryngeal cancers in a minimally invasive perspective [12]. Preclinical

Neurosurg Rev

and clinical studies by the team at the University of Pennsylvania have demonstrated the feasibility and safety of transoral resections with the assistance of da Vinci Surgical System to tumors of the head and neck [5]. This team introduced the term “Transoral robotic surgery” (TORS) to describe these procedures. Concerning the skull base field, literature with da Vinci remains very poor, including one cadaveric work that has permitted to reach the pituitary fossa by wide anterior bilateral maxillary antrostomies [11]. Transoral robot-assisted approaches have been performed for odontoidectomies [21, 22, 30], with one case reported by Lee et al. [20]. In 1985, Crockard has mentioned that “the transoral surgical approach allows access to structures from the sphenoid sinus rostrally to the fourth cervical vertebral body caudally” [3]. Despite this quotation and the new technical opportunities given by robot-assisted surgery, no transoral approach to the sella turcica has been attempted, without transpalatal drilling [25]. We assume that this fact is mainly explained by a technological deficiency, especially concerning two factors: first, the insufficient illumination to explore this deep and narrow anatomy and, secondly, the difficulty with usual instruments to target the sella. These two lacks could be dramatically changed with the da Vinci system, allowing to envision new perspectives in skull base approaches. The safety of transoral placement of the robotic endoscope and instruments has been established. Potential risks specific to the transoral use of the surgical robot include facial skin laceration, tooth injury, mucosal laceration, mandible fracture, cervical spine fracture, and ocular injury. Experiments performing skull base robotic surgery on a human cadaver with the da Vinci Surgical System demonstrate a safety profile similar to conventional transoral robotic surgery [5, 12]. Robotic surgery constitutes an additional step in the development of minimally invasive surgery for the approach of the skull base. This is the reason why we propose to define the feasibility and safety of such an innovative transoral transsphenoidal approach on human fresh cadavers with the da Vinci system, as well as to envision the advantages—and pitfalls—of this technique, comparatively to transnasal endoscopic surgery.

Methods Four human fresh cadavers were included in this work; all the specimens had fulfilled the “Centre du Don des Corps” criteria and had given their informed consent before death. All dissections were performed at the “Ecole Européenne de Chirurgie” with the da Vinci S HD 4 arms system (Intuitive Surgical®, Sunnyvale, CA, USA) even though only three arms were used (camera arm and two instrument arms). The robotic arms, called patient cart, stood at the head of the cadaver, placed supine next to a C-arm fluoroscope (operative

room plan in Fig. 1). A mouth retractor (type Doyen, Landanger®) was placed to get the usual transoral exposition. A 8.5-mm 30-degree-angled binocular endoscope, a 5-mm EndoWrist® Maryland dissector articulated, and a 5-mm EndoWrist® monopolar cautery instrument with a spatula tip were attached on the patient cart, respectively, on the middle, right, and left arms of the system. The three arms were brought into the oral cavity: the 30° video endoscope arm facing upwards on the midline and the two other robotic arms laterally, respecting teeth and labial commissures of the mouth (see Fig. 2). Two surgeons were necessary to proceed: one author, head and neck surgeon (SH), at the console and the other one, neurosurgeon (DC), next to the patient’s head to perform suction, to prevent from the robotic arms conflict with oral cavity structures and to perform bone drilling at the second time. First step of procedure was the retraction of the soft palate using two rubber catheters introduced in the nose and pulled out by the mouth. Then, the endoscope was pushed beyond the hard palate to offer an upward view of the cavum and the choanae. Mucosa of the posterior cavum, which corresponded to the mucosa covering anteriorly and inferiorly the sphenoidal rostrum, was dissected into a caudally base flap (see Fig. 3). Afterwards, the surgeons’ roles and the procedure changed as the left robotic arm was removed to get much space to the second surgeon, the endoscope remaining at the midline. The dissection of bony structures was performed by the neurosurgeon, watching his progression on the 2D flat-panel screen. The surgeon sitting at the console offered a second intraoperative control with 3D view, performed suction thanks to a dedicated robotic tool—8-mm EndoWrist® One TM suctionirrigator—and moved on demand the video endoscope while the neurosurgeon at the bedside drilled the skull base. This arrangement was mandatory so far, as no drilling instrument attached on the robotic arm was developed by Intuitive Surgical®. An electric motor (Bien-Air®) was employed with matchstick burs attached on a slightly angled handpiece. Before drilling the sphenoid, the attack angle of the instrument was checked by a lateral fluoroscopy, which was repeated several times during dissection. The sphenoid sinus was opened and enlarged to get a wide vision of the sella turcica. The latter was opened, and robotic arms were inserted into the sphenoid sinus to appreciate the maneuverability of the da Vinci EndoWrist® instruments in such a narrow space. After the dura mater was coagulated with monopolar instrument and opened, the pituitary gland resection was attempted. Final closure was performed with suture attempt. Times of each step—decomposed in installation, soft tissue dissection, bony dissection—were assessed. Unexpected difficulties were reported. Anatomical skull base features of the cadavers were noticed from lateral fluoroscopic view such as mouth opening,

Neurosurg Rev Fig. 1 Schematic view of the operative room. Surgeon 1 is the head and neck surgeon working at the console (SH); surgeon 2 is the neurosurgeon working at the bedside (DC)

hard palate length, and distance between posterior border of the hard palate and the lowest point of the sellar floor. Moreover, angles of work (described below) to the skull base had been measured. Type of sellar pneumatization was reported.

Results Cadavers were two males and two females, with mean age of 84 years old. Two specimens had no teeth, and mean mouth opening was 44.2 mm (min 41, max 48) (see Table 1). Mean hard palate length was 42 mm (min 40, max 44), and mean distance from hard palate to the sella was 45.5 mm (min 41, max 50). All sphenoidal sinuses were “sellar,” which meant

Fig. 2 Lateral intraoperative view. The three robotic arms stand in the oral cavity that is opened with a mouth retractor (type Doyen, Landanger®). The retraction of the soft palate is performed using two rubber catheters introduced in the nose and pulled out by the mouth. In the background, the C-arm fluoroscope for intraoperative 2D lateral control

that the pneumatization was situated below the sellar floor. The mean robotic setup time was 20 min (range 10 to 35 min), mean mucosal dissection time was 10 min (range 5 to 15 min), and transsphenoidal surgery including sphenoid drilling and sella opening was 30 min (range 15 to 60 min). Initial setup was achieved for all cadavers without any difficulties despite the anatomical heterogeneities of the specimens. The different shape and size of encountered soft palate did not disturb dissections. Once the 30° endoscope was inserted beyond the posterior border of the hard palate, visualization of the cavum was large enough to offer a perfect view on the Eustachian tube’s pharyngeal opening laterally and on the choanae superiorly (as shown in Fig. 3). Here, two structures were required as reference points: both sides’ choana and the posterior border of the vomer that provided an accurate midline landmark. As in other transsphenoidal approaches, keeping the dissection on the midline was mandatory. We did not experience lateral deviation in our dissections. The cavum mucosa was not always dissected in a whole flap (n=2) as tissues of cadavers were sometimes fragile. All the soft tissue sequences were performed easily with enough space to use the robotic instruments and without any tension on the oral cavity structures, especially the soft palate. The bony sequence was achieved placing the motor handpiece in the left labial commissure of the mouth. Indeed, the lateral movement of the handpiece, following naturally the lower teeth curve from the midline to the labial commissure, allowed an opening of the angle of work to the skull base (see Fig. 4). The latter was defined by the angle between the horizontal line passing through the hard palate and the projected line of the drill (as seen in Fig. 4 by dotted lines), which was placed at the midline and then in the labial commissure. From these comparative cadavers’ measurements, we observed that the mean angles of work were 55° (min 48, max 62) and 71.5° (min 67, max 76) for the midline and

Neurosurg Rev

Fig. 3 Intraoperative view with the 30° endoscope within the cavum. a The soft palate (1) is retracted using two rubber catheters at the top of the picture. The choanae are well visualized; right choana (2). 3 indicates a decisive landmark that corresponds to the articulation between the vomer and the sphenoid. 4 is the mucosa of the cavum. Greek small letter mu and pound sign are monopolar cautery and Maryland dissector, respectively. b The mucosal flap (6) is dissected with a caudal base in order to discover the rostrum of the sphenoid bone (5); the picture on the right bottom corner indicates the size of the flap, approximately 15 mm in width

the lateral positions, respectively. Thus, we hypothesized that the mean angle of work gain placing the drill in the labial

commissure was +16.5°. In all dissections, this trick had succeeded in approaching the sella turcica, and we had encountered no difficulty in this original approach. To prevent from a lateral deviation of the drilling, the angled feature of the handpiece was decisive. Opening the sphenoid sinus was achieved quickly (approximately 10 min), depending on the thickness of the sphenoidal rostrum. The video endoscope was successfully introduced within this sinus during all dissections and thus had provided a wide 3D view of the sella turcica and its surrounding structures (as shown in Fig. 5). Then, the pituitary fossa was opened with a thinner diamond drill. Indeed, the robotic arms reached the sella turcica in all procedures (see Fig. 6) with a correct manageability. After dural coagulation and opening, normal pituitary gland was removed with robotic instruments (see Fig. 7). Final view of the pituitary stalk and the optic chiasm was obtained, as shown in Fig. 7. Closure of a hypothetic cerebrospinal fluid leak from the pituitary fossa was facilitated by the great handling ability of EndoWrist® instruments in order to affix grafts or even to perform strong sutures of the mucosa. We succeeded in performing tremor-free sutures of the cavum mucosa, but we had encountered some difficulties to suture within the sella turcica because of its narrowness and the fragility of the sellar dura. At the end of the dissection, inspection of the oral cavity revealed no injury. This total surgical procedure was feasible with a 0° endoscope, but visualization of the choanae at the beginning and inside the sphenoid sinus at the end was much better with the 30° video endoscope, allowing a safer procedure. We hypothesized that transoral robotic-assisted surgery is feasible to reach the pituitary fossa with a minimally invasive approach and safe conditions.

Discussion We assume in this study that approaching the sella turcica by transoral robotic surgery (TORS) is feasible in a perspective of minimally invasive skull base procedure, with respect to

Table 1 Cadavers’ data and anatomical features measured from lateral fluoroscopy Cadavers

Sex

Age

Height

Weight (kg)

Mouth opening (mm)

HP length (mm)

Distance HP–ST (mm)

SS type

M angle (degree)

L angle (degree)

1 2 3 4

M M F F

85 76 91 84

1 1 1 1

86 73 60 65

45, no teeth 48 41, no teeth 43

44 41 43 40

47 44 41 50

Sellar Sellar Sellar Sellar

52 62 58 48

69 76 74 67

m 82 m 79 m 57 m 70

One can notice that all sphenoid sinus are “sellar,” which means that the pneumatization is posterior to the anterior wall of the sella turcica HP hard palate, ST sella turcica, SS sphenoidal sinus, M angle angle between the horizontal line passing through the hard palate and the projected line of the drill at the midline, L angle angle between the horizontal line passing through the hard palate and the projected line of the drill at the labial commissure

Neurosurg Rev

Fig. 4 Fluoroscopic lateral views, the endoscope standing at the midline of the mouth. On the left, the matchstick drill is inserted at the midline, and its projection on the sphenoid bone virtually meets the clivus (red dotted line). On the contrary, on the right picture, the bur is placed in the

labial commissure, and its projection clearly meets the sella turcica (green dotted line). This shows how the angle of work to the skull base is increased when the instruments are placed laterally in the oral cavity

certain rules. First, the mouth aperture must be normal, which means approximately 45 mm [33], as we have observed in this cadaveric work. One could oppose that dissections on cadavers from elderly people present some bias because of the teeth lack (as on two specimens in our study), assuming that edentulous specimens would present a larger mouth opening and thus a wider corridor to insert the robotic arms. In fact, we know from Gökçe et al. that edentulous patients have a reduced mouth aperture [6]; this has to be taken into account for further clinical applications. Secondly, the entry point in the sphenoid bone has to be defined after clear identification of

the choanae and the posterior edge of the vomer. According to this four-cadaver study, we propose that the “drilling key hole” should be placed just below the articulation between the vomer and the sphenoid body. Of course, the intraoperative fluoroscopic control is necessary, and further works might point out the feasibility of coupling da Vinci and neuronavigation systems. Finally, the analysis of the sphenoid sinus pneumatization will be mandatory for future patients. Hamberger et al. have firstly described three types of sphenoid sinus variations, which are still in use routinely [9]: conchal (absence of pneumatization), presellar (posterior border of the

Fig. 5 Intraoperative endoscopic view of the sella turcica. a Anatomical structures of the sphenoid sinus: (1) sellar floor, (2) dorsum sellae that is pneumatized, (3) left optic nerve protuberance, (4) right carotid protuberance, sellar portion, (5) right carotid protuberance, clival portion, and (6) opto-carotid recess. b Instrument placed in the pneumatized dorsum sellae and the corresponding fluoroscopic lateral picture (e). c instrument inserted in front of the anterior wall of the sella and the corresponding fluoroscopic view (d)

Neurosurg Rev

Fig. 6 Dissection with the robotic arms within the sphenoidal sinus. On the left side, endoscopic intraoperative view with the monopolar cautery anteriorly (Greek small letter mu) and the Maryland dissector posteriorly (pound sign), on each side of the sella turcica. On the right side, the

corresponding lateral fluoroscopy shows both instruments within the sphenoidal sinus. It is interesting to notice how the da Vinci EndoWrist® instruments reach this deep area with the great mobility of its extremities

sinus lined up on the anterior sellar wall), and sellar (sinus expanding inferiorly to the sella) types. Other authors have completed this classification over the years [29] and have established statistics [8, 10, 32]. For instance, Güldner et al. have assumed in their 580-patient series that 0.3 % have conchal, 6.6 % presellar, and 93.1 % sellar types [8]. The next patients eligible for skull base TORS will have a detailed sagittal bony window cranial CT scan to identify the type of sphenoid sinus pneumatization. In this transoral approach, the sphenoid bone is drilled from the bottom up, which means that

the sinus constitutes a security area before entering the pituitary fossa. This explains why conchal and presellar types are less ideal for TORS in a perspective of clinical applications. Fortunately, the sellar type is the most common, as previously mentioned [8]. This latter issue concerning the infero-superior approach of the sella turcica is a decisive point because it offers new possibilities for pituitary adenoma resection. In transsphenoidal surgery, with operating microscope or transnasal endoscope, the sella turcica is approached anterio-posteriorly with

Fig. 7 Intraoperative view of the pituitary fossa dissection. a View after sellar floor removal. b Cauterization of the sellar dura with the monopolar cautery (Greek small letter mu). c View during pituitary gland resection. d

Final view after removal. 1 sellar dura, 2 pneumatized dorsum sellae, 3 pituitary gland, 4 sellar diaphragm, 5 pituitary stalk retracted by a hook (ampersand), and 6 optic chiasm

Neurosurg Rev

satisfying results. When suprasellar extension is observed, this approach can be debated. Whether the extension is under 30 mm, transsphenoidal surgery remains possible, because of the usual softness of the adenoma [15], while larger suprasellar extension is associated with higher risks of incomplete resections [27]. This current TORS approach to the pituitary fossa allows envisioning new perspectives of tumor removals. Indeed, the working axis is totally modified from a horizontal plan to a vertical plan and so it corresponds with the tumor growth axis. Suprasellar macroadenoma, even with large upper extension, could be operated on with our technique. Moreover in such lesions, neurosurgeons sometimes need to let down the adenoma with blind movements. In TORS, the resection would be performed with a full real-time vision control, as we have shown that the endoscope and both robotic arms can be inserted into the sphenoid sinus. Furthermore for cerebrospinal fluid leak, it could be easier to create a watertight closure: by the maniability of the EndoWrist® instruments and by the possibility to perform sutures, as previously mentioned by Hanna et al. [11] and Lee et al. [21]. We have also attempted to perform dural sutures, but we assume that suturing a CSF leak within the sella turcica is very difficult, on the contrary to the clival dura. We have also tested the feasibility to affix tailored hydroxyapatite prosthesis in the sphenoid aperture and in the sella. It seems feasible because of the maniability of the robotic arms, but this has to be assessed in larger series. The mucosal closure is also improved [20, 22]. More generally, the surgeon gets back an operative gesture that is very close to the one performed under microscopic illumination, despite endoscopic conditions. This constitutes a very interesting input for young residents who want to learn robotic-assisted surgery. One previous team has performed TORS to reach the sella turcica on cadavers [11], but major differences with the presented study have to be mentioned. First, they have used a transnasal access for the video endoscope. Before making a pure transoral approach, we have tried to reproduce this technique, but we have encountered some difficulties to introduce the 8.5-mm endoscope without injuring the turbinates or the septum. This is the reason why we have decided to switch with a complete oral approach. Moreover, they have inserted the instruments by a wide bilateral anterior maxillary antrostomies that can be hardly included in a minimally invasive procedure. Despite all its promising applications, skull base TORS presents some limitations, as the surgical robot was not designed for transoral use. The size of the robotic arms and instruments does not always allow adequate exposure via a transoral approach. Good positioning of robotic arms is essential. Low constrain zones must be used to allow unrestricted mobilization of the robotic arms. Another limitation is the da Vinci system’s lack of force feedback. However, some authors emphasize that the excellent visual quality compensates this problem [30]. This is something that will be improved in the future with engineering developments. Another

matter is the absence of EndoWrist® “bony instruments,” such as drills, burs, and Kerrison punches. This makes impossible a pure robotic procedure so far. While one study mentions some prototypes of burs and rongeurs to perform spine surgery [24], these instruments are not yet used in routine. Placing the drilling handpiece in contact with the labial commissure entails risk of burns, as reported previously [14], and requires paying attention to the handpiece temperature. In the presented study, we have not used intubation set on cadavers, but we know from pharyngeal and laryngeal cancer surgeries that it does not disturb the robotic dissection [12]. Moreover, our mucosal dissection concerns the cavum, which is above the normal intubation tube position. Almost all skull base cadaveric works have been performed with two surgeons, the one at the bedside controlling his dissection on a 2D monitor [21, 22, 30]. While bony instruments are conceived and diffused, this issue could be bypassed if a 3D view system is created for the bedside surgeon, as mentioned by Lee et al. [20]. Even if a four-arm da Vinci robot is used and if the surgeon at the console successively controls the endoscope and the arms, the need of two surgeons for TORS is inevitable so far, as the second operator provides an essential assistance at the bedside. Endoscopic skull base approaches have the same features, except that the endoscope is held by the surgeon’s hand. Indeed, in case of longtime endoscopic procedures, fine tremor can occur and disturb both visualization and dissection. Finally, all new technologies that come into the surgical field must be discussed in a costeffectiveness perspective. Concerning the da Vinci system, it seems obvious that the number of procedures per year is the key point. Of course, further studies are warranted to compare this alternative technique with conventional microscopic or endoscopic procedures and to envision the benefits for the patients. We have reported some very simple features in the anatomical landmarks on fluoroscopy, such as mouth opening, hard palate length, and distance from hard palate to the sella. We have also assessed the angles of work at the midline (mean 55°) and laterally (mean 71.5°). From this four-specimen study, we assume that inserting the instruments laterally, at the level of the labial commissure, opens the skull base angle of work at approximately 16.5°, which seems significant to reach the sella turcica. This has to be confirmed on larger series. This is the reason why additional studies on the relation between the oral cavity and the sphenoid bone, as well as detailed angles of work assessments, are already in progress from patients’ CT scan data. Our robot-assisted preliminary series demonstrates the ability to approach the sella via oral approach without traumatic injury of nasal or oral cavity. Transoral approach avoids the complications of the endonasal resection: synechia, rhinitis sicca anterior, primary and secondary rhinitis atrophicans, and

Neurosurg Rev

empty nose syndrome. Skull base TORS is not a question of replacing the surgeons’ skills or just improving their intraoperative comfort. It is a matter of assisting the surgeon with motion scaling and 3D visualization within deep narrow spaces, such as the skull base. Conclusion This is the first description of transoral minimally invasive approach to the sella turcica with robotic assistance. Despite anatomical heterogeneities of the cadavers, the pituitary fossa seems to be operable by transoral route. This innovative technique could bring new insights in the pituitary adenoma treatment. Moreover, the maneuverability of the da Vinci system offers promising perspectives to envision watertight closure reinforcement. Acknowledgments The authors wish to thank Dr Aymeric Amelot, Dr Olivier André, Pr Guillaume Lot and Dr Stéphanie Trunet for their helpful contribution; the “Ligue contre le cancer” and the “Société française de Neurochirurgie - Laboratoire Codman” for their financial funding. The “Ecole Européenne de Chirurgie”, especially Aurore Dionnet, the “Centre du Don des Corps Université Paris Descartes” and Intuitive Surgical are acknowledged for their assistance. Disclosure The authors have no personal financial or institutional interest in any drugs, materials, or devices described in this article, except Antoine Missistrano who works for Intuitive Surgical.

References 1. Advincula AP, Song A (2007) The role of robotic surgery in gynecology. Curr Opin Obstet Gynecol 19:331–336 2. Carrau RL, Prevedello DM, de Lara D, Durmus K, Ozer E (2013) Combined transoral robotic surgery and endoscopic endonasal approach for the resection of extensive malignancies of the skull base. Head Neck 6 [epub ahead of print] 3. Crockard HA (1985) The transoral approach to the base of the brain and upper cervical cord. Ann R Coll Surg Engl 67:321–325 4. Dott NM, Bailey P (1925) A consideration of the hypophyseal adenomata. Br J Surg 13:314–366 5. Genden EM, O'Malley BW Jr, Weinstein GS, Stucken CL, Selber JC, Rinaldo A, Hockstein NG, Ozer E, Mallet Y, Satava RM, Moore EJ, Silver CE, Ferlito A (2012) Transoral robotic surgery: role in the management of upper aerodigestive tract tumors. Head Neck 34:886–893 6. Gökçe B, Destan UI, Ozpinar B, Sonugelen M (2009) Comparison of mouth opening angle between dentate and edentulous subjects. Cranio 27:174–179 7. Guiot G, Thibaut B (1959) L’extirpation des adénomes hypophysaires par voie trans-sphenoidale. Neurochirurgia 1:133–150 8. Güldner C, Pistorius SM, Diogo I, Bien S, Sesterhenn A, Werner JA (2012) Analysis of pneumatization and neurovascular structures of the sphenoid sinus using cone-beam tomography (CBT). Acta Radiol 53:214–219 9. Hamberger CA, Hammer G, Marcusson G (1961) Experiences in transantrosphenoidal hypophysectomy. Trans Pac Coast Otoophthalmol Soc Annu Meet 42:273–286

10. Hamid O, El Fiky L, Hassan O, Kotb A, El Fiky S (2008) Anatomic variations of the sphenoid sinus and their impact on trans-sphenoid pituitary surgery. Skull Base 18:9–15 11. Hanna EY, Holsinger C, DeMonte F, Kupferman M (2007) Robotic endoscopic surgery of the skull base: a novel surgical approach. Arch Otolaryngol Head Neck Surg 133:1209–1214 12. Hans S, Delas B, Gorphe P, Ménard M, Brasnu D (2012) Transoral robotic surgery in head and neck cancer. Eur Ann Otorhinolaryngol Head Neck Dis 129:32–37 13. Hardy J, Wigser SM (1965) Trans-sphenoidal surgery of pituitary fossa tumors with televised radiofluoroscopic control. J Neurosurg 23:612–619 14. Hirohi T, Yoshimura K (2010) Lower face reduction with fullthickness osteoctomy of mandibular corpus-angle followed by corticectomy. J Plast Reconstr Aesthet Surg 63:1251–1259 15. Honegger J, Ernemann U, Psaras T, Will B (2007) Objective criteria for successful transsphenoidal removal of suprasellar nonfunctioning pituitary adenomas. A prospective study. Acta Neurochir (Wien) 149:21–29 16. Jho HD, Carrau RL (1997) Endoscopic endonasal transsphenoidal surgery: experience with 50 patients. J Neurosurg 87:44–51 17. Kaptain GJ, Kanter AS, Hamilton DK, Laws ER (2011) Management and implications of intraoperative cerebrospinal fluid leak in transnasoseptal transsphenoidal microsurgery. Neurosurgery 68: 144–150 18. Kassam AB, Gardner PA, Snyderman CH, Carrau RL, Mintz AH, Prevedello DM (2008) Expanded endonasal approach, a fully endoscopic transnasal approach for the resection of midline suprasellar craniopharyngiomas: a new classification based on the infundibulum. J Neurosurg 108:715–728 19. Kassam AB, Gardner P, Snyderman C, Mintz A, Carrau R (2005) Expanded endonasal approach: fully endoscopic, completely transnasal approach to the middle third of the clivus, petrous bone, middle cranial fossa, and infratemporal fossa. Neurosurg Focus 19:E6 20. Lee JY, Lega B, Bhowmick D, Newman JG, O'Malley BW Jr, Weinstein GS, Grady MS, Welch WC (2010) Da Vinci robotassisted transoral odontoidectomy for basilar invagination. ORL J Otorhinolaryngol Relat Spec 72:91–95 21. Lee JY, O'Malley BW, Newman JG, Weinstein GS, Lega B, Diaz J, Grady MS (2010) Transoral robotic surgery of craniocervical junction and atlantoaxial spine: a cadaveric study. J Neurosurg Spine 12:13–18 22. Lee JY, O'Malley BW Jr, Newman JG, Weinstein GS, Lega B, Diaz J, Grady MS (2010) Transoral robotic surgery of the skull base: a cadaver and feasibility study. ORL J Otorhinolaryngol Relat Spec 72:181–187 23. Liu JK, Das K, Weiss MH, Laws ER Jr, Couldwell WT (2001) The history and evolution of transsphenoidal surgery. J Neurosurg 95(6): 1083–1096 24. Ponnusamy K, Chewning S, Mohr C (2009) Robotic approaches to the posterior spine. Spine (Phila Pa 1976) 34:2104–2109 25. Rose-Innes AP, Oosthuizen JH (1995) The transoral transpalatal approach to the pituitary fossa. Minim Invasive Neurosurg 38:22–26 26. Sade B, Mohr G, Frenkiel S (2006) Management of intra-operative cerebrospinal fluid leak in transnasal transsphenoidal pituitary microsurgery: use of post-operative lumbar drain and sellar reconstruction without fat packing. Acta Neurochir (Wien) 148:13–18 27. Saito K, Kuwayama A, Yamamoto N, Sugita K (1995) The transsphenoidal removal of nonfunctioning pituitary adenomas with suprasellar extensions: the open sella method and intentionally staged operation. Neurosurgery 36:668–675 28. Stippler M, Gardner PA, Snyderman CH, Carrau RL, Prevedello DM, Kassam AB (2009) Endoscopic endonasal approach for clival chordomas. Neurosurgery 64:268–277 29. Wang J, Bidari S, Inoue K, Yang H, Rhoton A Jr (2010) Extensions of the sphenoid sinus: a new classification. Neurosurgery 66:797–816 30. Yang MS, Yoon TH, Yoon do H, Kim KN, Pennant W, Ha Y (2011) Robot-assisted transoral odontoidectomy : experiment in new

Neurosurg Rev minimally invasive technology, a cadaveric study. J Korean Neurosurg Soc 49:248–251 31. Yates DR, Vaessen C, Roupret M (2011) From Leonardo to da Vinci: the history of robot-assisted surgery in urology. BJU Int 108:1708– 1713 32. Zada G, Agarwalla PK, Mukundan S Jr, Dunn I, Golby AJ, Laws ER Jr (2011) The neurosurgical anatomy of the sphenoid sinus and sellar floor in endoscopic transsphenoidal surgery. J Neurosurg 114:1319– 1330 33. Zawawi KH, Al-Badawi EA, Lobo SL, Melis M, Mehta NR (2003) An index for the measurement of normal maximum mouth opening. J Can Dent Assoc 69:737–741

Comments Tetsuya Goto, Kazuhiro Hongo, Matsumoto, Japan The authors demonstrated transsphenoidal pituitary surgery simulation using the da Vinci system via transoral approach. They concluded that the da Vinci system will be used for pituitary surgery with some modifications. The maneuverability of da Vinci system is remarkably superior to that of conventional endoscopic surgery. However, the endoscope and robot arm of da Vinci system are too large for routine transnasal endoscopic surgery. The transoral approach is the authors’ answer to solve this problem. Although we surgeons believe that better maneuverability allows for better surgery and must result in better outcome, this concept may be applicable in clinical situation only if the cost-benefit analysis can be ignored. Even the da Vinci system for laparoscopic surgery remains debatable with respect to cost-effectiveness (1, 2). The use of the new robotic application instead of conventional transsphenoidal surgery should at least be evaluated clinically by the surgical result. A clinical trial of endoscopic neurosurgery using da Vinci system is therefore expected. References 1. Knight J, Escobar PF. Cost and robotic surgery in gynecology. J Obstet Gynaecol Res. 40:12-7, 2014 2. Heemskerk J, Bouvy ND, Baeten CG. The end of robot-assisted laparoscopy? A critical appraisal of scientific evidence on the use of robot-assisted laparoscopic surgery. Surg Endosc. Nov 14. 2013 (letter to editor) Arya Nabavi, Kiel, Germany Chauvet et al. conducted a cadaveric study with the da Vinci Robotic system for transoral pituitary surgery. The potential of the robotic system as well as anatomical aspects of this unusual approach is described. While advanced visualization as well as the capacity for working in confined spaces (e.g., suturing in the depth) is enthusiastically discussed, the lack of customized instruments, particularly impeding the applicability of this robotic system in such a highly developed area as in pituitary surgery, is painfully obvious. Additionally, the bulk of the current robot design required the authors to use the alternate transoral route to the pituitary. To this end, they describe how they changed the procedure to accommodate the robot and provide appropriate measurements to quantify the preconditions of this approach. The authors went at length to find a way to use a tool. My initial reaction was bewilderment. However, the authors were willing to investigate “outside the box” and try something novel. For this, they should be commended. There are two features of this paper, which deserve more thorough discussion: the technology itself and a customized application thereof. The da Vinci system is without doubt the most advanced commercially available robotic system. High expectations in cardiac surgery (in the

beginning of the 2000s) were swiftly dampened due to restrictions in development of more custom-made tools and software (legal constraints) as well as the general limitations in regard to haptic feedback and visualization. Irrespective of these issues, distribution of the system was expanded into new surgical areas, i.e., GYN/OB, abdominal surgery, and most recently, urology. While there were improvements (particularly in visualization), the system retains the basic flaws in regard to haptics and lack of applicationoriented instruments as a result of restricted user-developer interaction. The multitude of application-related “technical notes” hardly enables an unbiased observer to determine the true value of this system. Nevertheless, users seem enthusiastic about this system and find very innovative “work-arounds” to employ the robot for those specific applications. Looking back almost a decade, the descriptions of the da Vinci capability remind the reader of an evidently high-level technological tool looking for an application. This becomes precarious, when surgical techniques are modified to accommodate the application of the tool. And this leads me to the second aspect, the alteration of a standard procedure to accommodate a new technology. The application of the da Vinci robot to pituitary surgery appears to make sense: we are working in the depth within a confined space and need perfect visualization. It seems that a robot could expand our abilities. However, as the authors discuss, special instruments are currently not integrated, necessitating drilling and basically operating the pituitary by a neurosurgeon “at the bedside.” Thus, the only present value of this robotic system concerns the approach. But since it is too bulky to be used for the established transnasal approach, another avenue is taken to accommodate the technology. This turns the world upside down. It should be the entities and the highest surgico-anatomic demands which decide how to approach a lesion and not the application of a tool. So, the initial reaction to using a transoral approach with a robot, which moreover is limited due to absent special tools, is to reject the pure notion. However, just as we returned to the transnasal route, when instruments became available, which made it feasible, we might consider another route if the technology would make it less hazardous to the patient. At present, the restraints of this system are more apparent than its advantages. Also, the giant proportions of the robot remain a bit disheartening. However, these restrictions can and surely will be addressed since skull base surgery seems a perfect venue for robotic assistance. Inclusion of navigation and intraoperative feedback (be it electrophysiology or imaging) together with collision detection could provide the means to excel this field even beyond the current high level. It is up to the physicians to take an active part in defining the specifications of such systems and their usefulness. Also, we should not accept “off-the shelf” tools as the final solution. Therefore, studies, such as this one, are essential to show current and conceivably permanent constrains. We can then decide, which limitations are prohibitive and which can be circumnavigated. But more importantly, we can identify important features, which the developers have to change to increase the practicability of the systems (like open interfaces for customized tools). Ultimately, some indications will be excluded. But maybe surprising areas of good application will emerge. In neurosurgery, we take a leading role in rapid developments, introducing technologies which revolutionize an entire field (e.g., microscope, endoscope, coils/stents). However, technologically savvy as we are, we have to ensure that thorough investigations determine the “value-add” of the technique, rather than merely its capacity to “do things differently.” While this cannot always be randomized controlled prospective studies, we should scrutinize new technology for its application within our current framework. But it is also imperative to carry on unprejudiced and reassess our ways, “thinking outside the box,” to grasp potentially useful innovations. To preserve and improve what we have achieved, we have to be aware that there are different ways and that there might be a better way. I commend the authors for their work. Hopefully, their original investigation will lead the company to be more flexible with their product, to comply to surgical needs and demands, rather than leaving the surgeons to change their ways.