- Email: [email protected]
Intradural endoscope-assisted anterior clinoidectomy: A cadaveric study
Clinical Neurology and Neurosurgery 115 (2013) 170–174
Contents lists available at SciVerse ScienceDirect
Clinical Neurology and Neurosurgery journal homepage: www.elsevier.com/locate/clineuro
Intradural endoscope-assisted anterior clinoidectomy: A cadaveric study Nishanta B. Baidya, Chi-Tun Tang, Mario Ammirati ∗ Department of Neurological Surgery, Ohio State University Medical Center, Columbus, OH, USA
a r t i c l e
i n f o
Article history: Received 25 August 2011 Received in revised form 4 March 2012 Accepted 6 May 2012 Available online 5 June 2012 Keywords: Anterior clinoidectomy Clinoidal internal carotid artery Endoscopy
a b s t r a c t Objective: The anterior clinoid process (ACP) is critically related to the clinoidal portion of the internal carotid artery (ICA). The deep location of the ACP makes treatment of vascular and neoplastic lesions related to the ACP challenging. Removal of the ACP is advocated to facilitate treatment of such lesions. However injury to the clinoidal ICA remains a potential and dreadful complication of ACP removal. The aim of this study was to demonstrate an endoscopic assisted technique to perform intradural removal of the ACP via a pterional approach with continuous visualization of the clinoidal ICA. Methods: Sixteen bilateral pterional dissections were performed in 8 glutaraldehyde embalmed, colored silicone injected, adult cadaveric heads. Using a standard pterional approach, we performed drilling of the ACP in 2 stages. Stage 1 consisted of extradural microscopic removal of the sphenoid ridge so as to gain access to the origin of the ACP. Stage 2, the endoscopic stage, consisted of intradural endoscopic removal of the ACP and mobilization of the clinoidal segment of the ICA. We used 2.7 mm, 0◦ and 30◦ angled endoscopes. Results: In all the specimens we were able to remove the ACP while at the same time continuously visualizing the clinoidal ICA. The exposure of the clinoidal ICA and of adjoining neuro-vascular structures including the intracranial optic nerve was excellent and was accomplished with minimal frontal lobe retraction. Mobilization of the clinoidal ICA led to unhindered exposure of the parasellar region. Conclusions: Endoscopic assisted ACP removal with continuous ICA visualization was feasible in our model. Continuous visualization of the clinoidal ICA should theoretically decrease the risk of inadvertent ICA injuries. Clinical studies to validate this laboratory study are necessary. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Surgical management of pathology within the paraclinoid and parasellar regions is challenging. This is due, at least in part, to the fact that the anterior clinoid process (ACP) covers this region and obscures its components. Therefore removal of the ACP facilitates surgery on these areas. However the ACP is closely related to the clinoidal segment of the internal carotid artery (ICA) as well as to the intracranial part of the optic nerve (ON), and the removal of the ACP is therefore associated with potential injury to the clinoidal and ophthalmic segments of the ICA, and the ON. Several techniques have been proposed to remove the ACP, both intradurally and extradurally, with or without endoscopic use [1–7]. None of these techniques has extensively discussed continuous visualization of the clinoidal ICA while removing the ACP and none of them has discussed intradural endoscopic removal of the ACP. We reasoned that continuous visualization of the clinoidal ICA while drilling the ACP could be advantageous in order to reduce risks to
the ICA. Therefore we investigated an endoscopic assisted technique that allows removal of the ACP under continuous clinoidal ICA visualization. 2. Materials and methods 2.1. Materials Eight glutaraldehyde embalmed, alcohol-preserved, colored silicon injected cadaveric heads were used in a total of 16 procedures. The procedures were performed using standard microsurgical instruments, a high-speed drill (Midas Rex, Medtronic, Inc., Minneapolis, MN, USA), a surgical microscope (Moller, Wedel, Germany), Budde-halo retractor system (Integra, Plainsboro, NJ, USA), microsurgical instruments and rigid endoscopes measuring 2.7 mm in outer diameter and 18 cm long with 0- and 30-◦ lenses (MINOP; Aesculap, Tuttlingen, Germany). 2.2. Methods
∗ Corresponding author at: Department of Neurological Surgery, N1025 Doan Hall, 410W, 10th Avenue Columbus, OH 43210, USA. Tel.: +1 614 293 1970; fax: +1 614 293 4024. E-mail address: [email protected] (M. Ammirati). 0303-8467/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.clineuro.2012.05.003
2.2.1. Dissection technique We performed a pterional craniotomy with the cadaveric head fixed in the supine position with Mayfield skull clamp and turned approximately 45◦ to the opposite side. The operating microscope
N.B. Baidya et al. / Clinical Neurology and Neurosurgery 115 (2013) 170–174
was used and the lesser wing of the sphenoid bone was removed extradurally, much as is in the standard pterional approach, described by Yasargil [8], until the meningo-orbital dural band (which marks the lateral edge of the superior orbital fissure) was reached. We divided the remainder of the dissection in 2 stages. 2.2.1.1. Stage I: microscopic stage. The meningo-orbital dural band was identified and a nick was made on it. The orbitofrontal dura was incised in a reversed-U fashion and reflected toward the cranial base. A one-fourth-inch retractor blade, attached to the Buddehalo retractor system, was then applied to support the frontal lobe in such a way that the orbital roof and the ACP were visualized intradurally. The dura overlying the ACP was detached in a triangular fashion by using an arachnoidal knife. This bare area is bounded by the root of the optic canal anteriorly, the lesser sphenoid wing laterally and the tip of the ACP posteriorly (Fig. 1A). The Sylvian fissure was not split. 2.2.1.2. Stage II: endoscopic stage. This stage, endoscopic anterior clinoidectomy, consisted of 3 steps; it was executed with 0◦ and 30◦ endoscopes. While the surgeon was drilling, the assistant surgeon was constantly irrigating and applying suction to the area of dissection by using a suction/irrigator device in order to render the simulated procedure as similar as possible to the real surgery. Continuous saline irrigation and suction are important not only to keep the surgical field clean but also to facilitate heat dissipation, and hence to minimize the possible heat related injuries to the adjacent neurovascular structures. The assistant surgeon was also holding the endoscope. 2.2.1.3. Step 1 – skeletonization of the ACP. The pilot drilling was started from the root of the lesser wing of the sphenoid bone (at the origin of the meningo-orbital band) with a 2 mm-wide cutting
171
burr. The drilling was extended in a lateral-to-medial direction following the dural flap medially toward the falciform ligament. This drilling was performed under 0◦ and 30◦ angled endoscopic guidance that allowed simultaneous visualization of the drill bit and of the clinoidal ICA (Fig. 1B). At the end of this step, the bulk of the ACP had been removed with only the small medial part and its base (optic strut) being left (Fig. 1C). 2.2.1.4. Step 2 – hollowing and complete removal of the ACP. During this phase both the 0◦ and 30◦ angled endoscopes were interchangeably used to visualize once more the under surface of the ACP and its inferomedially located clinoidal ICA. After replacing the cutting burr with a 1 mm-wide diamond burr, the remaining base of the ACP was hollowed and slowly skeletonized (Fig. 1D). After a plane of dissection between the tip of the ACP and the endosteal dura overlying the clinoidal ICA was created with a microdissector, the residual bony pieces were removed with the help of a micro curette and Kerrison rongeur (Fig. 1E). 2.2.1.5. Step 3 – mobilization of the clinoidal ICA. After the bony phase of the dissection was completed, the distal dural ring was cut on both its medial and lateral sides in order to free the clinoidal ICA; the falciform ligament was anteriorly cut as well. This final procedure facilitates mobilization of the optic nerve and of the proximal portion of the clinoidal ICA. 3. Results In all the specimens, we were able to reach the totality of the ACP with minimal retraction of the frontal lobe and without Sylvian fissure dissection. Moreover we were able to continuously visualize the clinoidal portion of the ICA throughout the drilling of the ACP. Also, the undersurface of the ACP could be seen in all the specimens during the clinoidectomy with the help of a 30◦ endoscope
Fig. 1. (A) Endoscopic view (0◦ endoscope): the triangle points to the bare area of the left anterior clinoid process after the overlying dura has been detached using the microscope. (B) Endoscopic view (0◦ endoscope): simultaneous view of the internal carotid artery (ICA), the anterior clinoid process (ACP) and the drill bit. (C) Endoscopic view (0◦ endoscope): the blue shaded area indicates the remnant of the left anterior clinoid process base after its major portion has been removed. The insert shows the optic strut (*) ICA, clinoidal internal carotid artery. (D) Endoscopic view (0◦ endoscope): the hollowed remaining base of the left anterior clinoid process (ACP) is shown. (E) Endoscopic view (0◦ endoscope): the left optic strut (OS) is visualized. The arrow points to the tip of the left anterior clinoid process, which is in the process of being removed.
172
N.B. Baidya et al. / Clinical Neurology and Neurosurgery 115 (2013) 170–174
Fig. 2. (A) Endoscopic view (30◦ endoscope): the undersurface of the left anterior clinoid process (*) is demonstrated. The clinoidal internal carotid artery (ICA) is seen lying inferomedial to the anterior clinoid process. The insert shows a microdissector between the anterior clinoid process (blue arrow) and the clinoidal internal carotid artery (ICA). (B) Endoscopic view (30◦ endoscope): the origin of the left ophthalmic artery (blue arrow) is shown together with the left clinoidal internal carotid artery (ICA) and the left optic nerve (CN II).
(Fig. 2A). The origin of the ophthalmic artery (OA) from the superomedial surface of the ophthalmic segment of the ICA (Fig. 2B) below the optic nerve was observed in 14 out of 16 dissections. The OA origin was better visualized with 30◦ endoscope. In all specimens the origins of the posterior communicating artery (PComA) and of the anterior choroidal artery (AChA) were clearly identified (Fig. 3A). In addition the terminal bifurcation of the ICA and the A1 segment of the anterior cerebral artery (ACA) and the M1 segment of the middle cerebral artery (MCA) were also seen. (Fig. 3B). In 4 specimens the ACP had a distinct vein in it (Fig. 3C). With 30◦ endoscope the intracranial portion of the optic nerve was also well visualized in all the cases (Fig. 2B). 4. Discussion 4.1. Anterior clinoid process The anatomy of the ACP and its relationship with surrounding structures has been extensively studied [4,9–12]. The ACP is a small triangle of bone with a 1-cm base and a 1-cm height [3]. Rhoton [13] has described the ACP as a posterior projection from the lesser wing of the sphenoid bone. According to his description, the base of the ACP continues with the adjacent sphenoid bone at three sites. Anteriorly the ACP base is attached at the medial edge of the sphenoid ridge, formed by the lesser sphenoid wing. Medially the base is attached to the anterior and posterior roots of the lesser wing. The anterior root extends medially from the base of the anterior clinoid to the body of the sphenoid bone and forms the roof of the optic canal. The posterior root (optic strut) extends medially below the optic nerve to the sphenoid body and forms the floor of the optic canal. The base of the anterior clinoid forms the lateral margin of the optic canal. The space obtained by removing the ACP is called the clinoidal space or area [14]. Together with the middle and posterior clinoid processes of the sphenoid bone; the ACP contributes to the superolateral boundary of the sella turcica. Even though pneumatization of the ACP has been reported in up to 9.2% of cases [15], we did not encounter any such pneumatization in our study. Clearly in clinical practice it is mandatory to be aware of the pneumatization of the ACP to avoid a post drilling complication such as Cerebrospinal fluid leaks [15]. 4.2. Clinoidal and ophthalmic segments of the internal carotid artery According to one classification system the ICA may be divided into 7 segments [16]. The clinoidal segment (C5) extends between the proximal and the distal dural rings while the
ophthalmic segment (C6) courses from the distal dural ring to the posterior communicating artery (PComA). The clinoidal segment is typically surrounded on three sides by bony structures, i.e., the ACP laterally, the optic strut anteriorly, and the tuberculum sellae medially [4]. The C5 and C6 segments of the ICA are the ones that are most at risk during removal of the ACP. The clinoidal and ophthalmic segments together are referred to as the paraclinoid ICA because of their intimacy with the ACP [3]. 4.3. Dural structures in relation to the ACP and the clinoidal ICA The ACP is tightly covered with dural folds [2]. Dura lining the anterior cranial fossa floor, anterior temporal fossa, and the sphenoid ridge converges at the ACP [3]. A thin fold of dura mater, the falciform ligament, extends medially from the ACP and covers a small segment of the optic nerve immediately proximal to the optic foramen [17]. As described by Lawton [3] there are two dural rings that are in close relation to the ACP and the clinoidal ICA. Dura from the superolateral aspect of the ACP extends medially in an oblique plane intersecting the ICA thus forming the distal dural ring. Similarly dura arising from the inferomedial aspect of the ACP runs medially in a flat axial plane that intersects with the ICA to form the proximal dural ring. Each dural ring defines important landmarks with the proximal dural ring marking the termination of the cavernous segment of the ICA and the beginning of the clinoidal segment, and the distal dural ring marking the termination of the clinoidal segment of the ICA and the beginning of its ophthalmic segment. The clinoidal segment of the ICA is located within a collar formed by the dura lining the medial surface of the ACP, the posterior surface of the optic strut, and the upper part of the carotid sulcus [6]. The ACP is also the site of attachment of the anteromedial part of the tentorium and the anterior petroclinoid and interclinoid dural folds [13]. 4.4. Neural structure in close relation to the ACP As described by Rhoton [18] the optic nerve has four parts: intraocular, intraorbital, intracanicular, and intracranial. Apart from its close relationship with the clinoidal internal carotid artery the anterior clinoid process is also critically related to the intracranial portion of the optic nerve. Once the intraorbital potion of the ON leaves the orbit the former becomes the intracanalicular ON and passes through the optic canal. After the intracanalicular ON has passed through the optic canal the intracranial portion of the ON runs along the medial aspect of the ACP before the optic nerve is directed posterior, superiorly, and medially toward the optic chiasm.
N.B. Baidya et al. / Clinical Neurology and Neurosurgery 115 (2013) 170–174
173
described in 1985 an extradural clinoidectomy that allows optimal mobilization of the optic nerve and of the internal carotid artery. Others have shown the importance of the anterior clinoidectomy to deal with vascular lesions such as internal carotid arteryophthalmic artery aneurysms, giant ICA aneurysms [7,24], clinoid and paraclinoid aneurysms [25], and basilar artery aneurysms [7]. In addition, removal of the ACP facilitates removal of non-vascular lesions such as sphenoid ridge meningiomas and suprasellar lesions including pituitary adenomas and craniopharyngiomas [7]. 4.6. Significance of the current study Using our technique we were able to accomplish complete ACP removal in all cases with continuous monitoring of the clinoidal ICA. This was accomplished using a combination of 0◦ and 30◦ endoscopes. The endoscope provided continuous panoramic views with adequate magnification of the ACP and its surrounding structures including the clinoidal and ophthalmic segments of the ICA. Our proposed technique contrasts with well-established techniques described by different authors [1–4,7,20,23,26] in many salient features. The key feature of our technique is that the anterior clinoidectomy is performed with a constant direct vision of the clinoidal ICA under endoscopic visualization. We feel that the constant vision of the undersurface of the ACP, and its inferomedially located clinoidal ICA, and medially located intracranial portion of the optic nerve, with the 30◦ endoscope, helps to avoid inadvertent injury to the clinoidal ICA and also to the optic nerve. Drawbacks of the use of the endoscope are the crowding of the surgical field by the endoscope, the lack of 3-d visualization, and the modest spatial and color distortion of the endoscopic image. The second key feature of our technique is that, without dissecting the Sylvian fissure, we were able to visualize the intradural ICA and its branches adjacent to the ACP such as the OA, PComA, AChA, ACA (A1), and MCA (M1). However in clinical practice dissection of the distal part of the fissure may be helpful to decrease tension on the perforating vessels. Another minor advantage is that frontal lobe retraction is minimal, thus decreasing potential complications. Even though we feel that our technique is anatomically safe by allowing continuous visualization of the critical structure (clinoidal ICA) while drilling, still extra care needs to be exercised during the later phases of the endoscopic resection of the ACP. At that stage an endosteal layer of dura should be maintained intact between the undersurface of the ACP and the clinoidal ICA in order to further minimize injury to the clinoidal ICA. 4.7. Limitations of this study Fig. 3. (A) Endoscopic view (0◦ endoscope): origins of the left posterior communicating artery (PComA) and a pair of the anterior choroidal arteries (AChA) are demonstrated. The microdissector is seen retracting the petroclinoid ligament (blue arrow) away from the posterior communicating artery. Oculomotor nerve (CN III) is between the PComA and the petroclinoid ligament (blue arrow). ICA, clinoidal internal carotid artery. (B) Endoscopic view (0◦ endoscope): the left internal carotid artery (ICA) is shown branching into the pre-bifurcation segment of the middle cerebral artery (M1) and the precommunicating segment of the anterior cerebral artery (A1). (C) Endoscopic view (0◦ endoscope): the left anterior clinoid process is visualized; the asterisk (*) is on the vein embedded in the anterior clinoid process.
4.5. Importance of anterior clinoidectomy The ACP is a surgically challenging structure because of its unique anatomy, deep skull base location, and its close proximity to the clinoidal ICA. However its removal clearly facilitates exposure of pathology in the parasellar area. Over the years, several authors have discussed the significance of the anterior clinoidectomy when approaching the paraclinoid and parasellar lesions [4,19–22], and dealing with the upper basilar artery [23]. Dolenc [1] originally
This is a cadaveric study and suffers from the limitation of all such studies. 5. Conclusions Our endoscopic assisted drilling of the ACP provides the capability of removing the ACP while continuously watching the clinoidal ICA. This feature could be advantageous in clinical practice in decreasing inadvertent injury to the ICA as well as to the optic nerve during drilling of the ACP. Clinical studies are needed to prove the validity of this statement.
Conflict of interest The authors report no conflict of interest concerning the materials or methods used in this study or the findings specifies in this paper. Final version of the manuscript was reviewed and approved it for submission by all authors.
174
N.B. Baidya et al. / Clinical Neurology and Neurosurgery 115 (2013) 170–174
References [1] Dolenc VV. A combined epi- and subdural direct approach to carotidophthalmic artery aneurysms. Journal of Neurosurgery 1985;62:667–72. [2] Komatsu F, Komatsu M, Tooru I, Manfred T. Endoscopic extradural anterior clinoidectomy via supraorbital keyhole: a cadaveric study. Neurosurgery 2011;68:334–8. [3] Lawton MT. Seven aneurysms. New York: Thieme; 2011. pp. 124–128. [4] Noguchi A, Balasingam V, Shiokawa Y, McMenomey SO, Delashaw JB. Extradural anterior clinoidectomy. Technical note. Journal of Neurosurgery 2005;102:945–50. [5] Ohmoto T, Nagao S, Mino S, Ito T, Honma Y, Fujiwara T. Exposure of the intracavernous carotid artery in aneurysm surgery. Neurosurgery 1991;28:317–24. [6] Seoane E, Rhoton Jr AL, de Oliveira E. Microsurgical anatomy of the dural collar (carotid collar) and rings around the clinoid segment of the internal carotid artery. Neurosurgery 1988;42:869–86. [7] Yonekawa Y, Ogata N, Imhof HG, Olivecrona M, Strommer K, Kwak TE, et al. Selective extradural anterior clinoidectomy for supra- and parasellar processes. Technical note. Journal of Neurosurgery 1997;87:636–42. [8] Yas¸argil MG. Microneurosurgery, vol. 1. New York: Thieme; 1984. pp. 215–233. [9] Day AL. Aneurysms of the ophthalmic segment. A clinical and anatomical analysis. Journal of Neurosurgery 1990;72:677–91. [10] Hayashi N, Masuoka T, Tomita T, Sato H, Ohtani O. Endo S. Surgical anatomy and efficient modification of procedures for selective extradural anterior clinoidectomy. Minimally Invasive Neurosurgery 2004;47(6):355–8. [11] Inoue T, Rhoton Jr AL, Theele D, Barry ME. Surgical approaches to the cavernous sinus: a microsurgical study. Neurosurgery 1990;26:903–32. [12] Knosp E, Müller G, Perneczky A. The paraclinoid carotid artery: anatomical aspects of a microneurosurgical approach. Neurosurgery 1988;22: 896–901. [13] Rhoton Jr AL. Rhoton cranial anatomy and surgical approaches. Philadelphia: Lippincott Williams & Wilkins; 2007. p. 413.
[14] Umansky F, Valarezo A, Elidan J. The superior wall of the cavernous sinus: a microanatomical study. Journal of Neurosurgery 1994;81:914–20. [15] Mikami T, Minamida Y, Koyanagi I, Baba T, Houkin K. Anatomical variations in pneumatization of the anterior clinoid process. Journal of Neurosurgery 2007;106:170–4. [16] Bouthillier A, van Loveren HR, Jeffrey TK. Segments of the internal carotid artery: a new classification. Neurosurgery 1996;38:425–33. [17] Rhoton Jr AL. Rhoton cranial anatomy and surgical approaches. Philadelphia: Lippincott Williams & Wilkins; 2007. p. 87. [18] Rhoton Jr AL. Rhoton cranial anatomy and surgical approaches. Philadelphia: Lippincott Williams & Wilkins; 2007. p. 342. [19] Citric I, Rosenblatt S. Suprasellar meningiomas. Neurosurgery 2001;49:1372–9. [20] Evans JJ, Hwang YS, Lee JH. Pre- versus post-anterior clinoidectomy measurement of the optic nerve, internal carotid artery, and opticocarotid triangle: a cadaveric morphometric study. Neurosurgery 2000;46: 1018–23. [21] Lee JH, Jeun S-S, Evans J, Kosmorsky G. Surgical management of clinoidal meningiomas. Neurosurgery 2001;48:1012–21. [22] Nutik SL. Removal of the anterior clinoid process for exposure of the proximal intracranial carotid artery. Journal of Neurosurgery 1988;69:529–34. [23] Day JD, Giannotta SL, Fukushima T. Extradural temporopolar approach to lesions of the upper basilar artery and infrachiasmatic region. Journal of Neurosurgery 1994;81:230–5. [24] Heros RC, Nelson PB, Ojemann RG, Crowell RM, DeBrun G. Large and giant paraclinoid aneurysms: surgical techniques, complications, and results. Neurosurgery 1983;12:153–63. [25] De Jesu ˇıs O, Sekhar LN, Reidel CJ. Clinoid and paraclinoid aneurysms: surgical anatomy, operative techniques, and outcome. Surgical Neurology 1999;51:477–87. [26] Takahashi JA, Kawarazaki A, Hashimoto N. Intradural en-bloc removal of the anterior clinoid process. Neurosurgical technique. Acta Neurochirurgica 2004;146:505–9.
Contents lists available at SciVerse ScienceDirect
Clinical Neurology and Neurosurgery journal homepage: www.elsevier.com/locate/clineuro
Intradural endoscope-assisted anterior clinoidectomy: A cadaveric study Nishanta B. Baidya, Chi-Tun Tang, Mario Ammirati ∗ Department of Neurological Surgery, Ohio State University Medical Center, Columbus, OH, USA
a r t i c l e
i n f o
Article history: Received 25 August 2011 Received in revised form 4 March 2012 Accepted 6 May 2012 Available online 5 June 2012 Keywords: Anterior clinoidectomy Clinoidal internal carotid artery Endoscopy
a b s t r a c t Objective: The anterior clinoid process (ACP) is critically related to the clinoidal portion of the internal carotid artery (ICA). The deep location of the ACP makes treatment of vascular and neoplastic lesions related to the ACP challenging. Removal of the ACP is advocated to facilitate treatment of such lesions. However injury to the clinoidal ICA remains a potential and dreadful complication of ACP removal. The aim of this study was to demonstrate an endoscopic assisted technique to perform intradural removal of the ACP via a pterional approach with continuous visualization of the clinoidal ICA. Methods: Sixteen bilateral pterional dissections were performed in 8 glutaraldehyde embalmed, colored silicone injected, adult cadaveric heads. Using a standard pterional approach, we performed drilling of the ACP in 2 stages. Stage 1 consisted of extradural microscopic removal of the sphenoid ridge so as to gain access to the origin of the ACP. Stage 2, the endoscopic stage, consisted of intradural endoscopic removal of the ACP and mobilization of the clinoidal segment of the ICA. We used 2.7 mm, 0◦ and 30◦ angled endoscopes. Results: In all the specimens we were able to remove the ACP while at the same time continuously visualizing the clinoidal ICA. The exposure of the clinoidal ICA and of adjoining neuro-vascular structures including the intracranial optic nerve was excellent and was accomplished with minimal frontal lobe retraction. Mobilization of the clinoidal ICA led to unhindered exposure of the parasellar region. Conclusions: Endoscopic assisted ACP removal with continuous ICA visualization was feasible in our model. Continuous visualization of the clinoidal ICA should theoretically decrease the risk of inadvertent ICA injuries. Clinical studies to validate this laboratory study are necessary. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Surgical management of pathology within the paraclinoid and parasellar regions is challenging. This is due, at least in part, to the fact that the anterior clinoid process (ACP) covers this region and obscures its components. Therefore removal of the ACP facilitates surgery on these areas. However the ACP is closely related to the clinoidal segment of the internal carotid artery (ICA) as well as to the intracranial part of the optic nerve (ON), and the removal of the ACP is therefore associated with potential injury to the clinoidal and ophthalmic segments of the ICA, and the ON. Several techniques have been proposed to remove the ACP, both intradurally and extradurally, with or without endoscopic use [1–7]. None of these techniques has extensively discussed continuous visualization of the clinoidal ICA while removing the ACP and none of them has discussed intradural endoscopic removal of the ACP. We reasoned that continuous visualization of the clinoidal ICA while drilling the ACP could be advantageous in order to reduce risks to
the ICA. Therefore we investigated an endoscopic assisted technique that allows removal of the ACP under continuous clinoidal ICA visualization. 2. Materials and methods 2.1. Materials Eight glutaraldehyde embalmed, alcohol-preserved, colored silicon injected cadaveric heads were used in a total of 16 procedures. The procedures were performed using standard microsurgical instruments, a high-speed drill (Midas Rex, Medtronic, Inc., Minneapolis, MN, USA), a surgical microscope (Moller, Wedel, Germany), Budde-halo retractor system (Integra, Plainsboro, NJ, USA), microsurgical instruments and rigid endoscopes measuring 2.7 mm in outer diameter and 18 cm long with 0- and 30-◦ lenses (MINOP; Aesculap, Tuttlingen, Germany). 2.2. Methods
∗ Corresponding author at: Department of Neurological Surgery, N1025 Doan Hall, 410W, 10th Avenue Columbus, OH 43210, USA. Tel.: +1 614 293 1970; fax: +1 614 293 4024. E-mail address: [email protected] (M. Ammirati). 0303-8467/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.clineuro.2012.05.003
2.2.1. Dissection technique We performed a pterional craniotomy with the cadaveric head fixed in the supine position with Mayfield skull clamp and turned approximately 45◦ to the opposite side. The operating microscope
N.B. Baidya et al. / Clinical Neurology and Neurosurgery 115 (2013) 170–174
was used and the lesser wing of the sphenoid bone was removed extradurally, much as is in the standard pterional approach, described by Yasargil [8], until the meningo-orbital dural band (which marks the lateral edge of the superior orbital fissure) was reached. We divided the remainder of the dissection in 2 stages. 2.2.1.1. Stage I: microscopic stage. The meningo-orbital dural band was identified and a nick was made on it. The orbitofrontal dura was incised in a reversed-U fashion and reflected toward the cranial base. A one-fourth-inch retractor blade, attached to the Buddehalo retractor system, was then applied to support the frontal lobe in such a way that the orbital roof and the ACP were visualized intradurally. The dura overlying the ACP was detached in a triangular fashion by using an arachnoidal knife. This bare area is bounded by the root of the optic canal anteriorly, the lesser sphenoid wing laterally and the tip of the ACP posteriorly (Fig. 1A). The Sylvian fissure was not split. 2.2.1.2. Stage II: endoscopic stage. This stage, endoscopic anterior clinoidectomy, consisted of 3 steps; it was executed with 0◦ and 30◦ endoscopes. While the surgeon was drilling, the assistant surgeon was constantly irrigating and applying suction to the area of dissection by using a suction/irrigator device in order to render the simulated procedure as similar as possible to the real surgery. Continuous saline irrigation and suction are important not only to keep the surgical field clean but also to facilitate heat dissipation, and hence to minimize the possible heat related injuries to the adjacent neurovascular structures. The assistant surgeon was also holding the endoscope. 2.2.1.3. Step 1 – skeletonization of the ACP. The pilot drilling was started from the root of the lesser wing of the sphenoid bone (at the origin of the meningo-orbital band) with a 2 mm-wide cutting
171
burr. The drilling was extended in a lateral-to-medial direction following the dural flap medially toward the falciform ligament. This drilling was performed under 0◦ and 30◦ angled endoscopic guidance that allowed simultaneous visualization of the drill bit and of the clinoidal ICA (Fig. 1B). At the end of this step, the bulk of the ACP had been removed with only the small medial part and its base (optic strut) being left (Fig. 1C). 2.2.1.4. Step 2 – hollowing and complete removal of the ACP. During this phase both the 0◦ and 30◦ angled endoscopes were interchangeably used to visualize once more the under surface of the ACP and its inferomedially located clinoidal ICA. After replacing the cutting burr with a 1 mm-wide diamond burr, the remaining base of the ACP was hollowed and slowly skeletonized (Fig. 1D). After a plane of dissection between the tip of the ACP and the endosteal dura overlying the clinoidal ICA was created with a microdissector, the residual bony pieces were removed with the help of a micro curette and Kerrison rongeur (Fig. 1E). 2.2.1.5. Step 3 – mobilization of the clinoidal ICA. After the bony phase of the dissection was completed, the distal dural ring was cut on both its medial and lateral sides in order to free the clinoidal ICA; the falciform ligament was anteriorly cut as well. This final procedure facilitates mobilization of the optic nerve and of the proximal portion of the clinoidal ICA. 3. Results In all the specimens, we were able to reach the totality of the ACP with minimal retraction of the frontal lobe and without Sylvian fissure dissection. Moreover we were able to continuously visualize the clinoidal portion of the ICA throughout the drilling of the ACP. Also, the undersurface of the ACP could be seen in all the specimens during the clinoidectomy with the help of a 30◦ endoscope
Fig. 1. (A) Endoscopic view (0◦ endoscope): the triangle points to the bare area of the left anterior clinoid process after the overlying dura has been detached using the microscope. (B) Endoscopic view (0◦ endoscope): simultaneous view of the internal carotid artery (ICA), the anterior clinoid process (ACP) and the drill bit. (C) Endoscopic view (0◦ endoscope): the blue shaded area indicates the remnant of the left anterior clinoid process base after its major portion has been removed. The insert shows the optic strut (*) ICA, clinoidal internal carotid artery. (D) Endoscopic view (0◦ endoscope): the hollowed remaining base of the left anterior clinoid process (ACP) is shown. (E) Endoscopic view (0◦ endoscope): the left optic strut (OS) is visualized. The arrow points to the tip of the left anterior clinoid process, which is in the process of being removed.
172
N.B. Baidya et al. / Clinical Neurology and Neurosurgery 115 (2013) 170–174
Fig. 2. (A) Endoscopic view (30◦ endoscope): the undersurface of the left anterior clinoid process (*) is demonstrated. The clinoidal internal carotid artery (ICA) is seen lying inferomedial to the anterior clinoid process. The insert shows a microdissector between the anterior clinoid process (blue arrow) and the clinoidal internal carotid artery (ICA). (B) Endoscopic view (30◦ endoscope): the origin of the left ophthalmic artery (blue arrow) is shown together with the left clinoidal internal carotid artery (ICA) and the left optic nerve (CN II).
(Fig. 2A). The origin of the ophthalmic artery (OA) from the superomedial surface of the ophthalmic segment of the ICA (Fig. 2B) below the optic nerve was observed in 14 out of 16 dissections. The OA origin was better visualized with 30◦ endoscope. In all specimens the origins of the posterior communicating artery (PComA) and of the anterior choroidal artery (AChA) were clearly identified (Fig. 3A). In addition the terminal bifurcation of the ICA and the A1 segment of the anterior cerebral artery (ACA) and the M1 segment of the middle cerebral artery (MCA) were also seen. (Fig. 3B). In 4 specimens the ACP had a distinct vein in it (Fig. 3C). With 30◦ endoscope the intracranial portion of the optic nerve was also well visualized in all the cases (Fig. 2B). 4. Discussion 4.1. Anterior clinoid process The anatomy of the ACP and its relationship with surrounding structures has been extensively studied [4,9–12]. The ACP is a small triangle of bone with a 1-cm base and a 1-cm height [3]. Rhoton [13] has described the ACP as a posterior projection from the lesser wing of the sphenoid bone. According to his description, the base of the ACP continues with the adjacent sphenoid bone at three sites. Anteriorly the ACP base is attached at the medial edge of the sphenoid ridge, formed by the lesser sphenoid wing. Medially the base is attached to the anterior and posterior roots of the lesser wing. The anterior root extends medially from the base of the anterior clinoid to the body of the sphenoid bone and forms the roof of the optic canal. The posterior root (optic strut) extends medially below the optic nerve to the sphenoid body and forms the floor of the optic canal. The base of the anterior clinoid forms the lateral margin of the optic canal. The space obtained by removing the ACP is called the clinoidal space or area [14]. Together with the middle and posterior clinoid processes of the sphenoid bone; the ACP contributes to the superolateral boundary of the sella turcica. Even though pneumatization of the ACP has been reported in up to 9.2% of cases [15], we did not encounter any such pneumatization in our study. Clearly in clinical practice it is mandatory to be aware of the pneumatization of the ACP to avoid a post drilling complication such as Cerebrospinal fluid leaks [15]. 4.2. Clinoidal and ophthalmic segments of the internal carotid artery According to one classification system the ICA may be divided into 7 segments [16]. The clinoidal segment (C5) extends between the proximal and the distal dural rings while the
ophthalmic segment (C6) courses from the distal dural ring to the posterior communicating artery (PComA). The clinoidal segment is typically surrounded on three sides by bony structures, i.e., the ACP laterally, the optic strut anteriorly, and the tuberculum sellae medially [4]. The C5 and C6 segments of the ICA are the ones that are most at risk during removal of the ACP. The clinoidal and ophthalmic segments together are referred to as the paraclinoid ICA because of their intimacy with the ACP [3]. 4.3. Dural structures in relation to the ACP and the clinoidal ICA The ACP is tightly covered with dural folds [2]. Dura lining the anterior cranial fossa floor, anterior temporal fossa, and the sphenoid ridge converges at the ACP [3]. A thin fold of dura mater, the falciform ligament, extends medially from the ACP and covers a small segment of the optic nerve immediately proximal to the optic foramen [17]. As described by Lawton [3] there are two dural rings that are in close relation to the ACP and the clinoidal ICA. Dura from the superolateral aspect of the ACP extends medially in an oblique plane intersecting the ICA thus forming the distal dural ring. Similarly dura arising from the inferomedial aspect of the ACP runs medially in a flat axial plane that intersects with the ICA to form the proximal dural ring. Each dural ring defines important landmarks with the proximal dural ring marking the termination of the cavernous segment of the ICA and the beginning of the clinoidal segment, and the distal dural ring marking the termination of the clinoidal segment of the ICA and the beginning of its ophthalmic segment. The clinoidal segment of the ICA is located within a collar formed by the dura lining the medial surface of the ACP, the posterior surface of the optic strut, and the upper part of the carotid sulcus [6]. The ACP is also the site of attachment of the anteromedial part of the tentorium and the anterior petroclinoid and interclinoid dural folds [13]. 4.4. Neural structure in close relation to the ACP As described by Rhoton [18] the optic nerve has four parts: intraocular, intraorbital, intracanicular, and intracranial. Apart from its close relationship with the clinoidal internal carotid artery the anterior clinoid process is also critically related to the intracranial portion of the optic nerve. Once the intraorbital potion of the ON leaves the orbit the former becomes the intracanalicular ON and passes through the optic canal. After the intracanalicular ON has passed through the optic canal the intracranial portion of the ON runs along the medial aspect of the ACP before the optic nerve is directed posterior, superiorly, and medially toward the optic chiasm.
N.B. Baidya et al. / Clinical Neurology and Neurosurgery 115 (2013) 170–174
173
described in 1985 an extradural clinoidectomy that allows optimal mobilization of the optic nerve and of the internal carotid artery. Others have shown the importance of the anterior clinoidectomy to deal with vascular lesions such as internal carotid arteryophthalmic artery aneurysms, giant ICA aneurysms [7,24], clinoid and paraclinoid aneurysms [25], and basilar artery aneurysms [7]. In addition, removal of the ACP facilitates removal of non-vascular lesions such as sphenoid ridge meningiomas and suprasellar lesions including pituitary adenomas and craniopharyngiomas [7]. 4.6. Significance of the current study Using our technique we were able to accomplish complete ACP removal in all cases with continuous monitoring of the clinoidal ICA. This was accomplished using a combination of 0◦ and 30◦ endoscopes. The endoscope provided continuous panoramic views with adequate magnification of the ACP and its surrounding structures including the clinoidal and ophthalmic segments of the ICA. Our proposed technique contrasts with well-established techniques described by different authors [1–4,7,20,23,26] in many salient features. The key feature of our technique is that the anterior clinoidectomy is performed with a constant direct vision of the clinoidal ICA under endoscopic visualization. We feel that the constant vision of the undersurface of the ACP, and its inferomedially located clinoidal ICA, and medially located intracranial portion of the optic nerve, with the 30◦ endoscope, helps to avoid inadvertent injury to the clinoidal ICA and also to the optic nerve. Drawbacks of the use of the endoscope are the crowding of the surgical field by the endoscope, the lack of 3-d visualization, and the modest spatial and color distortion of the endoscopic image. The second key feature of our technique is that, without dissecting the Sylvian fissure, we were able to visualize the intradural ICA and its branches adjacent to the ACP such as the OA, PComA, AChA, ACA (A1), and MCA (M1). However in clinical practice dissection of the distal part of the fissure may be helpful to decrease tension on the perforating vessels. Another minor advantage is that frontal lobe retraction is minimal, thus decreasing potential complications. Even though we feel that our technique is anatomically safe by allowing continuous visualization of the critical structure (clinoidal ICA) while drilling, still extra care needs to be exercised during the later phases of the endoscopic resection of the ACP. At that stage an endosteal layer of dura should be maintained intact between the undersurface of the ACP and the clinoidal ICA in order to further minimize injury to the clinoidal ICA. 4.7. Limitations of this study Fig. 3. (A) Endoscopic view (0◦ endoscope): origins of the left posterior communicating artery (PComA) and a pair of the anterior choroidal arteries (AChA) are demonstrated. The microdissector is seen retracting the petroclinoid ligament (blue arrow) away from the posterior communicating artery. Oculomotor nerve (CN III) is between the PComA and the petroclinoid ligament (blue arrow). ICA, clinoidal internal carotid artery. (B) Endoscopic view (0◦ endoscope): the left internal carotid artery (ICA) is shown branching into the pre-bifurcation segment of the middle cerebral artery (M1) and the precommunicating segment of the anterior cerebral artery (A1). (C) Endoscopic view (0◦ endoscope): the left anterior clinoid process is visualized; the asterisk (*) is on the vein embedded in the anterior clinoid process.
4.5. Importance of anterior clinoidectomy The ACP is a surgically challenging structure because of its unique anatomy, deep skull base location, and its close proximity to the clinoidal ICA. However its removal clearly facilitates exposure of pathology in the parasellar area. Over the years, several authors have discussed the significance of the anterior clinoidectomy when approaching the paraclinoid and parasellar lesions [4,19–22], and dealing with the upper basilar artery [23]. Dolenc [1] originally
This is a cadaveric study and suffers from the limitation of all such studies. 5. Conclusions Our endoscopic assisted drilling of the ACP provides the capability of removing the ACP while continuously watching the clinoidal ICA. This feature could be advantageous in clinical practice in decreasing inadvertent injury to the ICA as well as to the optic nerve during drilling of the ACP. Clinical studies are needed to prove the validity of this statement.
Conflict of interest The authors report no conflict of interest concerning the materials or methods used in this study or the findings specifies in this paper. Final version of the manuscript was reviewed and approved it for submission by all authors.
174
N.B. Baidya et al. / Clinical Neurology and Neurosurgery 115 (2013) 170–174
References [1] Dolenc VV. A combined epi- and subdural direct approach to carotidophthalmic artery aneurysms. Journal of Neurosurgery 1985;62:667–72. [2] Komatsu F, Komatsu M, Tooru I, Manfred T. Endoscopic extradural anterior clinoidectomy via supraorbital keyhole: a cadaveric study. Neurosurgery 2011;68:334–8. [3] Lawton MT. Seven aneurysms. New York: Thieme; 2011. pp. 124–128. [4] Noguchi A, Balasingam V, Shiokawa Y, McMenomey SO, Delashaw JB. Extradural anterior clinoidectomy. Technical note. Journal of Neurosurgery 2005;102:945–50. [5] Ohmoto T, Nagao S, Mino S, Ito T, Honma Y, Fujiwara T. Exposure of the intracavernous carotid artery in aneurysm surgery. Neurosurgery 1991;28:317–24. [6] Seoane E, Rhoton Jr AL, de Oliveira E. Microsurgical anatomy of the dural collar (carotid collar) and rings around the clinoid segment of the internal carotid artery. Neurosurgery 1988;42:869–86. [7] Yonekawa Y, Ogata N, Imhof HG, Olivecrona M, Strommer K, Kwak TE, et al. Selective extradural anterior clinoidectomy for supra- and parasellar processes. Technical note. Journal of Neurosurgery 1997;87:636–42. [8] Yas¸argil MG. Microneurosurgery, vol. 1. New York: Thieme; 1984. pp. 215–233. [9] Day AL. Aneurysms of the ophthalmic segment. A clinical and anatomical analysis. Journal of Neurosurgery 1990;72:677–91. [10] Hayashi N, Masuoka T, Tomita T, Sato H, Ohtani O. Endo S. Surgical anatomy and efficient modification of procedures for selective extradural anterior clinoidectomy. Minimally Invasive Neurosurgery 2004;47(6):355–8. [11] Inoue T, Rhoton Jr AL, Theele D, Barry ME. Surgical approaches to the cavernous sinus: a microsurgical study. Neurosurgery 1990;26:903–32. [12] Knosp E, Müller G, Perneczky A. The paraclinoid carotid artery: anatomical aspects of a microneurosurgical approach. Neurosurgery 1988;22: 896–901. [13] Rhoton Jr AL. Rhoton cranial anatomy and surgical approaches. Philadelphia: Lippincott Williams & Wilkins; 2007. p. 413.
[14] Umansky F, Valarezo A, Elidan J. The superior wall of the cavernous sinus: a microanatomical study. Journal of Neurosurgery 1994;81:914–20. [15] Mikami T, Minamida Y, Koyanagi I, Baba T, Houkin K. Anatomical variations in pneumatization of the anterior clinoid process. Journal of Neurosurgery 2007;106:170–4. [16] Bouthillier A, van Loveren HR, Jeffrey TK. Segments of the internal carotid artery: a new classification. Neurosurgery 1996;38:425–33. [17] Rhoton Jr AL. Rhoton cranial anatomy and surgical approaches. Philadelphia: Lippincott Williams & Wilkins; 2007. p. 87. [18] Rhoton Jr AL. Rhoton cranial anatomy and surgical approaches. Philadelphia: Lippincott Williams & Wilkins; 2007. p. 342. [19] Citric I, Rosenblatt S. Suprasellar meningiomas. Neurosurgery 2001;49:1372–9. [20] Evans JJ, Hwang YS, Lee JH. Pre- versus post-anterior clinoidectomy measurement of the optic nerve, internal carotid artery, and opticocarotid triangle: a cadaveric morphometric study. Neurosurgery 2000;46: 1018–23. [21] Lee JH, Jeun S-S, Evans J, Kosmorsky G. Surgical management of clinoidal meningiomas. Neurosurgery 2001;48:1012–21. [22] Nutik SL. Removal of the anterior clinoid process for exposure of the proximal intracranial carotid artery. Journal of Neurosurgery 1988;69:529–34. [23] Day JD, Giannotta SL, Fukushima T. Extradural temporopolar approach to lesions of the upper basilar artery and infrachiasmatic region. Journal of Neurosurgery 1994;81:230–5. [24] Heros RC, Nelson PB, Ojemann RG, Crowell RM, DeBrun G. Large and giant paraclinoid aneurysms: surgical techniques, complications, and results. Neurosurgery 1983;12:153–63. [25] De Jesu ˇıs O, Sekhar LN, Reidel CJ. Clinoid and paraclinoid aneurysms: surgical anatomy, operative techniques, and outcome. Surgical Neurology 1999;51:477–87. [26] Takahashi JA, Kawarazaki A, Hashimoto N. Intradural en-bloc removal of the anterior clinoid process. Neurosurgical technique. Acta Neurochirurgica 2004;146:505–9.