Comparison between the microscope and endoscope in the direct endonasal extended transsphenoidal approach: anatomical study

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1 J Neurosurg 104: , 2006 Comparison between the microscope and endoscope in the direct endonasal extended transsphenoidal approach: anatomical study DOMENICO CATAPANO, M.D., CHRIS A. SLOFFER, M.D., GIORGIO FRANK, M.D., ERNESTO PASQUINI, M.D., VINCENZO A. D ANGELO, M.D., AND GIUSEPPE LANZINO, M.D. Department of Neurosurgery, Microsurgical Laboratory, Illinois Neurological Institute, University of Illinois College of Medicine at Peoria, Illinois; Department of Neurosurgery, Bellaria Hospital, Bologna; Department of Otolaryngology, Sant Orsola-Malpighi University Hospital, Bologna; and Neurosurgical Department, Casa Sollievo della Sofferenza Hospital, San Giovanni Rotondo, Italy Object. The authors compare the views afforded by the operating microscope and the endoscope in the direct endonasal extended transsphenoidal approach to the sellar, suprasellar, and parasellar regions. Methods. Five formalin-fixed, silicone-injected adult cadaveric heads were studied. A direct endonasal transsphenoidal approach was performed via the right nostril, pushing aside the nasal septum. The approach was performed with the microscope first, then with the endoscope. For each step (sellar, suprasellar, and clival), the exposure afforded by direct microscopic view was measured and then compared with that obtained using the endoscope. The direct endonasal approach provides a slightly off-midline view. Although the microscope provides an adequate view of the midline structures and part of the contralateral parasellar areas, the addition of the endoscope allows for a more panoramic view and permits widening of the approach in all directions. Conclusions. An adequate exposure of the sellar, suprasellar, and infrasellar/upper clival regions can be achieved via a simple, direct endonasal approach. From a direct endonasal route, there is a preferential visualization of the structures contralateral to the approach. The endoscope affords a more panoramic view that extends the area covered by the operating microscope. KEY WORDS extended transsphenoidal approach operating microscope endoscope sellar region T HE evolution of modern neurosurgical techniques indicates a continuous trend toward less traumatic procedures. One neurosurgical field in which the concept of minimal invasiveness is amplified is the surgical management of sellar and parasellar lesions. As a result of this evolutionary process, a direct endonasal transsphenoidal approach has become increasingly popular when dealing with pituitary tumors. This modification of Hirsch s original endonasal rhinoseptal route 30,34,39 was first proposed by Griffith and Veerapen in It avoids an anterior nasal or sublabial incision, no anterior dissection of the nasal septum is necessary, and it requires only minimal dissection of the posterior nasal mucosa. This approach is better tolerated (with less postoperative pain) and is more direct (requiring less operative time) than the more traditional sublabial or rhinoseptal routes. 5,21,27,45,46 Since Weiss 44 original description of the extended transsphenoidal approach to the parasellar region, other authors have reported successful resection, via various extensions and modifications of the classic transsphenoidal approach, Abbreviation used in this paper: ICA = internal carotid artery. of lesions other than pituitary adenomas that were located in the suprasellar and clival compartments. 2,11,14,18 20,25,26,28,29,31 33, Most of these authors have reached the sellar region via a sublabial or rhinoseptal approach. The direct endonasal route has seldom been used 6,11,12,15,31 in the extended transsphenoidal approach because of concerns that it provides a more restricted exposure than the more traditional rhinoseptal and sublabial ones. In addition, the trajectory and angle of view obtained with the direct endonasal route are slightly off the midline. 9,11,15,31,43 The combined use of the operating microscope and the endoscope at different stages of the operation may overcome some of these limitations. This anatomical study was conducted to compare the view provided by the operating microscope with that afforded by the endoscope in the extended transsphenoidal approach made through a direct endonasal route. Materials and Methods Preparation and Initial Dissection Five formalin-fixed human adult cadaveric heads were studied. The arterial and venous systems were injected with colored silicone that was distributed under pressure through the ICAs, the vertebral 419

2 D. Catapano, et al. FIG. 1. Left and Right: View through the operating microscope at the sellar level. Left: The bone of the sellar floor and the bone limiting the medial wall of the contralateral cavernous sinus were removed with the aid of the operating microscope. After opening of the dura, the pituitary gland, the contralateral intracavernous ICA (I.C.A.), the anterior and inferior intercavernous sinuses (asterisks) and the inferior hypophysial arteries (I.Hyp.A.) can be seen. Right: After changing the angle and the orientation of the microscope, the contralateral intracavernous ICA was partially exposed. arteries, and the internal jugular veins. A direct endonasal transsphenoidal approach was performed through one nostril (on the right side). The approach was then extended by removing bone to expose the cavernous sinuses, the suprasellar region, and the clival area. For each of these steps (exposure of sellar and cavernous sinus, suprasellar area, and infrasellar/clival area), the initial dissection was performed with the aid of an operating microscope (model M695; Leica, Wetzlar, Germany). Endoscopes that were 4 mm in diameter and 18 and 30 cm in length (the shorter one was used for the initial portion of the exposure and the longer one for the deeper portion), both with 0 lenses (Storz, Tuttlingen, Germany), were then inserted, and for each step both a quantitative and qualitative comparison of the visualized structures was made. Pictures of each step were taken using a digital camera (D1x; Nikon, Tokyo, Japan) for the view through the operating microscope, and a digital recorder (AIDA DVD; Storz) was used for the endoscopic view. FIG. 2. Same specimen as in Fig. 1, showing an endoscopic view of the sellar and cavernous sinus exposure. After removing the bone of the sellar floor and extending the bone exposure as far laterally as possible with the aid of the direct microscopic view (area encircled by black line), the endoscope was inserted. With this device we confirmed almost complete exposure of the sellar floor, and we also confirmed the slightly off-midline exposure with preferential uncovering guided by the direct microscopic view of the contralateral structures, including part of the contralateral intracavernous ICA. The ipsilateral carotid prominence is clearly recognizable. In this picture, the bone removal was extended, guided by the microscopic view, to the planum sphenoidale and the clival/infrasellar region. Asterisks designate the opticocarotid recess. Bas. = basilar; II C.N. = second cranial nerve (optic nerve); Sphen. = sphenoidale. Nasal Phase The nasal procedure was performed with the aid of the microscope. After visualization of the inferior turbinate and the nasal septum, the middle turbinate was identified rostral to the inferior turbinate. The choana was reached by following the inferior margin of the middle turbinate. The sphenoidal ostium was identified superolateral to the choana. Pushing the middle and superior turbinate laterally expanded the paraseptal surgical corridor. The nasal mucosa overlying the ipsilateral rostrum was incised and the rostrum exposed. The nasal septum and vomer were detached from the rostrum with a septal breaker. The septum was pushed contralaterally and a submucosal dissection was extended to the contralateral sphenoidal ostium. A partial posterior ethmoidectomy was then performed to obtain a wider superolateral exposure. A Hardy bivalve speculum was positioned. Transsphenoidal Phase and Extended Approach The anterior wall of the sphenoid sinus between the two sphenoid 420

3 Direct endonasal extended transsphenoidal approach ostia was opened with 1- and 2-mm Kerrison rongeurs, aided by direct microscopic views. After opening the anterior wall of the sinus and removing any sphenoid septum/septa and the mucous membranes, the bone landmarks within the structure (floor of the sella turcica, carotid prominences, opticocarotid recess, tuberculum sellae, prechiasmatic groove, planum sphenoidale, and posterior wall of the sphenoid sinus) were identified as much as possible with the microscope and then confirmed with the endoscope. The sellar floor was opened as widely as possible, initially under direct microscopic view. The speculum was then removed and the endoscope inserted. The amount of bone exposed with the aid of direct microscopic view was measured with a ruler, using the panoramic view offered by the endoscope. Additional bone was then removed under the guidance of direct endoscopic visualization, and additional measurements were taken. These steps (maximal exposure guided by the direct microscopic view, followed by measurements and additional exposure performed with the aid of endoscopic visualization) were repeated for the suprasellar and clival exposure. Results Sellar and Cavernous Sinus Exposure A small opening was first made in the anterior wall of the sella turcica with the high-speed drill, using the microscopic view as a guide. This opening was then widened using a Kerrison rongeur to include the floor and anterior wall of the sella turcica and the cavernous sinuses as far laterally as possible. The dura mater was then cut along the bone opening and removed. In all specimens, the ipsilateral parasellar ICA was not visualized with the microscope. On the other hand, the parasellar ICA was visible for various lengths on the contralateral side in each specimen. Nevertheless, in no case was it possible to visualize with the microscope the anterior loop of the intracavernous ICA on the side contralateral to the approach (Fig. 1). After removing as much of the sellar floor as possible with the aid of the direct microscopic view, the endoscope was inserted and measurements were taken. With the endoscope it was demonstrated that the sellar compartment had been exposed for 90% of its extent (range 80 95%), with the missed portion of the sellar floor lying on the ipsilateral side (Fig. 2). Because the endoscope allowed easy visualization of the impressions of both ICAs in the lateral wall of the sphenoid sinus, the distance between the two ICAs was measured by drawing an imaginary line passing through the center of the pituitary gland. This distance was 19 mm (range mm). The amount of bone removed with the aid of direct microscopic visualization on either side from the center of the pituitary gland measured 6.5 mm (range 5 9 mm) on the side ipsilateral to the approach, and 12.5 mm (range mm) on the contralateral side (this included some of the bone removed over the carotid artery on this side). With the guidance of the direct endoscopic view it was possible to extend the exposure of the sellar floor and the cavernous sinus. This allowed an additional exposure, when compared with the one facilitated by the direct microscopic view, of 6 mm (range 4 8 mm) on the ipsilateral side. With this additional uncovering, complete exposure of the anterior loop of the cavernous ICA could be achieved in each specimen. Bone removal guided by the direct endoscopic view allowed further lateral extension of 4 mm (range 3 5 mm) on the contralateral side. With this additional amount of bone removed on the contralateral side, the entire medial portion of the cavernous ICA and its anterior loop could TABLE 1 Mean amount of bone removal measured from the midline in the coronal plane in cadaveric heads be visualized and exposed. Overall, adding the endoscope allowed extension of the total bone removal guided by direct vision to a mean of 12.5 mm on the ipsilateral side and 16.5 mm on the contralateral side (the distance was measured from the center of the pituitary gland to the most lateral extension of the approach; see Table 1). Suprasellar Exposure Bone Removal (mean distance [mm] from midline) Suprasellar Level Sellar Level Infrasellar Level Aided By Ipsilat Contralat Ipsilat Contralat Ipsilat Contralat microscope endoscope* total removal * Pluses denote additional exposure made possible by endoscopic guidance. After slightly extending the head and/or manipulating the speculum to point more superiorly, bone removal was extended anteriorly with the aid of the direct microscopic view to include the tuberculum sellae, the prechiasmatic groove, and the posterior part of the planum sphenoidale. The bone was removed using either a high-speed drill or a Kerrison rongeur, as dictated by the bone thickness. Bone removal could be comfortably extended anterior to the tuberculum sellae with the aid of the operating microscope, for 17.5 mm (range mm) anterior to the anterior intercavernous sinus in the sagittal plane. The bone removal could be extended laterally with the aid of the microscope for a total width (measured from an imaginary line joining the middle of the pituitary gland with the middle point between the two opticocarotid recesses) of 5.5 mm (range 4 7 mm) ipsilateral to the approach, and a mean distance of 8 mm (range 6 9 mm) on the contralateral side (Table 1). The anterior intercavernous sinus demarcates the insertion of the diaphragma sellae into the tuberculum sellae. The suprasellar cistern is exposed by dividing the anterior intercavernous sinus and diaphragma sellae, and then opening the dura mater overlying the tuberculum sellae and chiasmatic sulcus. Dissection of the arachnoid trabeculae allows visualization of the pituitary stalk, the superior hypophysial arteries, the A 1 portion of both anterior cerebral arteries, the anterior communicating artery complex, the optic chiasm, and the lamina terminalis (Fig. 3). Using the endoscope at this stage (that is, after bone removal and dural opening with the aid of the operating microscope) allowed extension of bone removal for an additional 3 mm (range 2 4 mm) anteriorly. Under direct endoscopic vision, the lateral extension could be widened by an additional 4 mm (range 2 5 mm) on the ipsilateral and 4 mm (range 3 5 mm) on the contralateral side (Fig. 4). The total extension of bone removal after combining the views provided by the microscope and endoscope reached a length of 20.5 mm anterior to the anterior intercavernous sinus in the sagittal plane. The total lateral-to-lateral extension of the bone opening from the midline reached 9.5 mm 421

4 D. Catapano, et al. After slight flexion of the head and/or manipulation of the speculum to point more inferiorly, the posterior wall of the sphenoid sinus, with part of the clivus, was removed with the high-speed drill or a Kerrison punch as dictated by the bone thickness. The dura mater was then cut along the bone opening and removed. Our exposure encompassed that portion of the clivus that can be comfortably uncovered via the transsphenoidal approach. No effort was made to extend the inferior exposure by dividing the rhinopharynx. In three of five specimens, we were able to identify with the microscope the infrasellar carotid artery protuberance on the contralateral side. Guided by the direct microscopic view, the exposure could be extended by 15 mm in the sagittal plane (range mm) from the posterior intercavernous sinus in a rostral-to-caudal direction. The lateral extent of bone removal possible with the aid of direct microscopic vision, calculated from a posterior extension of the line joining the midpoint of the opticocarotid recesses with the middle of the pituitary gland, totaled 6 mm (range 5 7 mm) ipsilaterally and 10 mm (range 8 11 mm) on the side contralateral to the approach. With this amount of bone removal, the medial surface of the contralateral vertical segment of the ICA could be partially exposed. After dural opening, the basilar artery could be visualized for a variable extent of its course. The endoscope s panoramic view made it possible to gain an additional 4 mm (range 3 5 mm) in width on the ipsilateral side, reaching the anterior surface of the vertical segment of the ICA. On the contralateral side it was possible to gain another 3 mm (range 2 4 mm); this allowed visualization of the anterior and medial surface of the vertical ICA segment. The amount of bone removed using the microscopic view initially, and a direct endoscopic view afterward, measured 10 mm in width ipsilaterally and 13 mm on the contralateral side (Table 1). There was no gain in the rostral-to-caudal extension of this approach with the endoscope, because the anatomical boundaries of the sphenoid sinus limited the degree of orientation of the endoscope. Figure 5 shows the comparative overall views provided by the microscope and subsequent insertion of the endoscope after bone removal and dural opening. FIG. 3. View through the operating microscope of a suprasellar exposure. The bone constituting the tuberculum and the posterior part of the planum sphenoidale has been removed and the exposed dura mater opened. The diaphragma sellae has been removed. After dissection of the arachnoid trabeculae, it is possible to visualize the pituitary stalk, the optic chiasm, and the optic nerves. The contralateral superior hypophysial artery (S.Hyp.A.) arising in the chiasmatic cistern and passing medially to reach the stalk and chiasm is visualized. The contralateral distal dural ring and the floor of the optic canal have been removed to expose the ophthalmic artery (Oph.A.) coursing below the optic nerve. The anterior cerebral arteries and anterior communicating artery (A.Com.A.), which course above the optic chiasm and the lamina terminalis (asterisk), and the contralateral recurrent artery of Heubner (Rec.A.) are also visible. on the ipsilateral and 12 mm on the contralateral side (Table 1). Clival Exposure Discussion Following Schloffer s 42 first transnasal transsphenoidal approach to a pituitary lesion in 1906, this approach has undergone continuous evolution, with modifications devised and reported by numerous skilled surgeons. 8,16,17 With the further development of modern microinstrumentation, the transsphenoidal approach has rapidly become the preferred route used to remove the majority of lesions confined to the sella turcica. Until the last decade, the preferred route to reach the sella was the sublabial transseptal approach, as originally described by Cushing. 8 In recent years, the endonasal transseptal approach originally described by Hirsch and reviewed by others 30,34,39 has gained popularity because it eliminates a sublabial incision with its associated risk of lip numbness and oronasal fistulas, while still providing adequate exposure of the sella turcica. Using these two classic transsphenoidal routes (the sublabial and rhinoseptal), several authors have reported extension of the approach in the suprasellar, cavernous sinus, and infrasellar/clival regions. 2,11,14,19,20,25,26,28,29,31 33,36 38,44 As neurosurgical techniques have evolved toward less invasive approaches, a direct endonasal route has been increasingly used. This route is minimally invasive and has the potential advantage of a simpler and faster nasal dissection with fewer postoperative nasal problems. It affords a more restricted exposure and a trajectory that is slightly off the midline, 9,15, 31,43 however, compared with the more traditional endonasal or sublabial transseptal approaches. 7,35,41 For this reason, the direct endonasal route has seldom been used in dealing with midline suprasellar and infrasellar/clival lesions 1,3,4,6,10,12,13, 22 24,31,40,46 via the extended transsphenoidal approach. In our study, we were able to demonstrate that the use of the endoscope allows for further extension of the sellar, su- 422

5 Direct endonasal extended transsphenoidal approach FIG. 4. Same specimen as in Fig. 3, showing an endoscopic view of the suprasellar exposure. The bone removal and dural opening have been extended with the aid of the endoscope. The panoramic view afforded by this device offers better visualization of a wider operative field. The asterisk designates the lamina terminalis. Front. Br. = frontal branches. FIG. 5. Overall endoscopic view available after bone removal and dural opening. The area encircled by the black line represents the area exposed for direct microscopic view. The more panoramic view offered by the endoscope is obvious when compared with the area comfortably exposed with the aid of the operating microscope. The direct endonasal route affords an approach that is slightly off the midline (the white line designates the midline of the sellar and parasellar structures). Extension of the approach with the aid of the endoscope allows the following to be accomplished: completion of the sellar opening on the ipsilateral side; completion of the exposure of the ICA on the contralateral side; exposure of the ICA on the ipsilateral side; opening of the first tract of the optic canals on both sides; and both lateral and anterior extension of the upper part of the operative field through the planum sphenoidale. A.I.C.A. = anterior inferior cerebellar artery; B.A. = basilar artery; Hyp. = hypophysis; Lam. Term. = lamina terminalis; P.C.A. = posterior cerebral artery; S.C.A. = superior cerebellar artery. 423

6 D. Catapano, et al. prasellar, and clival exposure, even through a simple direct endonasal route. The relatively narrower exposure provided by the direct endonasal approach compared with the sublabial route is no longer a limitation, once the full potential of the endoscope is used. With the endoscope, the entire area of the suprasellar, infrasellar, and parasellar regions can be exposed. The lateral boundaries of the areas exposed are represented by the optic canals anteriorly, whereas at the sellar and infrasellar/clival level the lateral anatomical limits are represented by the ICA profile. Using the endoscope, the structures forming the natural anatomical boundaries of the extended approach are easily visualized, particularly on the contralateral side. Our study also confirms that the trajectory afforded by the direct endonasal view (with or without the endoscope) provides preferential visualization of structures contralateral to the side of the approach. The slightly off-midline trajectory provided by the endonasal route can be used to advantage in the extended transsphenoidal approach, because the majority of midline suprasellar and clival lesions tend to have a preferential unilateral extension. When the lesion is not perfectly symmetrical across the midline, it should be approached through the nostril contralateral to the side of preferential extension of the lesion. Our study supports the use of a pure endoscopic technique through a direct endonasal route. Nevertheless, if the surgeon is not completely comfortable with a pure endoscopic technique, then a combined microscopic endoscopic approach can be used. The combined use of the microscope and endoscope allows the surgeon to take advantage of the three-dimensional visualization provided by the microscope and the more panoramic view afforded by the endoscope, which allows further extension of the exposed areas. If a combined approach is used, the need for a rigid speculum to be in place does limit the space available for the endoscope and the instruments. Thus, in a combined microscopic endoscopic technique the entire potential of the endoscope may not be fully used. Conclusions An adequate exposure of the sellar, suprasellar, and infrasellar/upper clival regions can be achieved through a simple direct endonasal exposure. The endoscope affords a more panoramic view that allows extension of the area covered by the operating microscope. When using the direct endonasal route, the structures contralateral to the approach are preferentially visualized with the microscope, whereas the endoscope is particularly useful for better visualization of the structures ipsilateral to the approach. Acknowledgments We acknowledge Storz (Tuttlingen, Germany), which provided the endoscopes and the endoscopic instruments used in this study. 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