Endoscopic Endonasal Approach to the Maxillary Strut: Anatomical Review and Case Series

Transcription

1 The Laryngoscope VC 2014 The American Laryngological, Rhinological and Otological Society, Inc. Endoscopic Endonasal Approach to the Maxillary Strut: Anatomical Review and Case Series Sanjeet S. Grewal, MD; Almaz Kurbanov, MD; Amjad Anaizi, MD; Jeffrey T. Keller, PhD; Philip V. Theodosopoulos, MD; Lee A. Zimmer, MD, PhD Objectives/Hypothesis: The maxillary strut is the bone that separates the foramen rotundum and superior orbital fissure. Tumors involving the lateral wall of the sphenoid sinus, posterior ethmoid, or posterior maxillary sinus may invade this region. The authors detail the anatomy of the strut and present a case series that emphasizes the importance and utility of this useful landmark during an endoscopic endonasal approach to lesions in this region. Study Design: Cadaveric dissections and retrospective case series. Methods: Endoscopic endonasal dissections were performed on six formalin-fixed cadaver heads. Morphometric analyses of 100 skulls were conducted using CT scans and BrainLab. Four patients underwent procedures that exposed the maxillary strut. Results: The maxillary strut was trapezoidal shaped with an average cross-sectional area of mm 2 and average thickness of mm. The maxillary strut was present bilaterally in all skulls examined. Anteroposterior length averaged mm on the right and mm on the left. Our patient series illustrated the clinical utility of the maxillary strut as a landmark during endoscopic approaches to the skull base. Conclusions: An endoscopic endonasal approach can be used to expose the maxillary strut. Improved understanding of this anatomy is important to achieving success when using this approach for the biopsy or resection of lesions in the lateral sellar compartment, pterygopalatine fossa, and aspects of the middle cranial fossa. Key Words: Endoscopy, pterygopalatine fossa, skull base surgery, trigeminal nerve, anatomy. Level of Evidence: N/A. Laryngoscope, 124: , 2014 INTRODUCTION Since the original description of endoscopic approaches for pituitary disease was provided, interest in transnasal endoscopic skull-base surgery has increased. Transnasal, transmaxillary, transethmoid, and transphenoidal endoscopic approaches provide a customizable surgical approach to various skull base tumors Approaches to the pterygopalatine (PtPF) fossa are of special interest to both otolaryngologists and neurosurgeons. Subsequent to the initial description of the endonasal, endoscopic sphenopalatine artery ligation, several anatomic descriptions of this small but anatomically complex region have been published Furthermore, access to the infratemporal fossa, petrous apex, and Meckel s cave lesions requires navigation within the region of the PtPF. 17,18 From the Department of Otolaryngology, Head and Neck Surgery (L.A.Z.); and the Department of Neurosurgery (L.A.Z., S.S.G., A.K., A.A., J.T.K., P.V.T.), University of Cincinnati College of Medicine; the Neurosensory Disorders Center at University of Cincinnati Neuroscience Institute (L.A.Z., S.S.G., A.K., A.A., J.T.K., P.V.T.); and the Mayfield Clinic (L.A.Z., J.T.K., P.V.T.), Cincinnati, Ohio, U.S.A. Editor s Note: This Manuscript was accepted for publication November 18, The authors have no funding, financial relationships, or conflicts of interest to disclose. Send correspondence to Lee A. Zimmer, MD, PhD, Department of Otolaryngology, Head and Neck Surgery, University of Cincinnati College of Medicine, 231 Albert Sabin Way, ML 0528, Cincinnati OH lee.zimmer@uc.edu DOI: /lary Benign and malignant neoplasms, as well as infectious processes of the nasal cavity and paranasal sinuses, may invade the pterygopalatine fossa. Invasion of this fossa results in the spread of the pathology to multiple regions of the skull base, including the inferior orbital fissure and retrobulbar space via the pterygomaxillary fissure to the infratemporal fossa and masticator space, the sphenopalatine foramen to the nasal cavity, the greater palatine canal to the palate, and the foramen rotundum (FR) and pterygoid canal to the middle cranial fossa Knowledge of both the potential pathways of tumor progression and the anatomy transgressed by tumor spread is critical for its endoscopic removal. The maxillary strut, a bony projection of the greater wing of the sphenoid, divides the embryological foramen lacerum anterius into the foramen rotundum and the superior orbital fissure (SOF). The medial aspect of the maxillary strut is the medial portion of the pterygoid process and the lateral wall of the sphenoid sinus. The lateral border of this strut is the temporal lobe dura. We describe the endoscopic anatomy of the maxillary strut and adjacent structures in cadaveric and morphometric studies (Fig. 1 and Fig. 2) and highlight its importance as a landmark in this retrospective cases series. MATERIALS AND METHODS Of six cadaveric heads for dissection, two specimens were frozen cadaveric heads and four specimens were fresh cadaveric heads in which the internal carotid arteries (ICAs) and internal 1739

2 The nasal mucosa over the crista ethmoidalis was then elevated to identify the sphenopalatine palatine artery as it exits the pterygopalatine fossa. Using a Kerrison Rongeur (Karl Storz, Tuttingen, Germany), the surgeon removed bone laterally from the posterior wall of the maxillary antrum to the lateral border of the pterygoid plate. Fat lying posterior to the posterior maxillary wall was then bluntly dissected to identify the contents of the pterygopalatine fossa. The internal maxillary artery was dissected from the more posteriorly located infraorbital and vidian nerves. The infraorbital nerve was then dissected in a posterior and medial direction to the inferior orbital fissure, and then to the foramen rotundum (Fig. 2A). The posterior lateral wall of the sphenoid sinus was then removed to expose the internal carotid artery and the optic nerve. At this point, a 30-degree lens was used to provide better visualization. Bone was dissected from the lateral wall of the sphenoid sinus to expose the orbital apex and cavernous sinus. Bone overlying the medial surface of the foramen rotundum was removed with a high-speed 3-mm drill, allowing visualization of V2 and dissection toward the cavernous sinus and Meckel s cave. Following V2 back toward the cavernous sinus led to the maxillary strut, which was identified between the contents of the SOF and V2 (Fig. 2B). Removal of this bone with a combination of a Kerrison Rongeur and a high-speed diamond drill (Stryker, Kalamazoo, MI) allowed access to the dura of the middle cranial fossa (Fig. 2C and D). Fig. 1. Maxillary strut of dry skull viewed through an endoscopic endonasal approach. A) From CT scans, BrainLab software (Feldkirchen, Germany) was used to measure its cross sectional area. B) Caliper used to measure the anteroposterior length of the maxillary strut, between the inferior aspect of the superior orbital fissure and the superior rim of foramen rotundum. MS 5 maxillary strut. jugular veins were injected with colored latex solution before dissection. 22 Bilateral dissection of the maxillary sinus, sphenoid sinus, and pterygopalatine fossa were performed using 0-degree endoscopy (total 12 sides) and standard rhinologic/ skull base instrumentation. Images were captured with a Stryker 1288 high-definition imaging system (Kalamazoo, MI) with Medtronic 0- and 30-degree endoscopes (Jacksonville, FL). Surgical Technique All surgical descriptions pertain to a left-sided endoscopic endonasal approach via a transmaxillary and transphenoidal approach. Dissections were performed with a combination of 0- and 30-degree 4-mm nasal endoscopes (Medtronic). After the head was positioned in a cupped holder, a large maxillary antrostomy was performed endoscopically, preserving the inferior and middle turbinates. The limits of the maxillary antrostomy included the lacrimal bone, inferior turbinate, lamina papyracea, and posterior maxillary antrum. A complete anterior and posterior ethmoidectomy and sphenoidotomy were performed on the left, and the sphenoidotomy was extended to the lateral wall of the sphenoid sinus. Anatomical Measurements Using calipers, we measured the anteroposterior (AP) length of the strut on 100 dry skulls. With CT scans of the dry skulls, BrainLab (Feldkirchen, Germany) software was then used to determine the cross-sectional area and thickness of the strut accessed through an endoscopic endonasal approach (Fig. 1A and B). Results are presented as mean 6 standard error of mean (SEM). Illustrating the relevance of the maxillary strut as a landmark in endoscopic procedures, our retrospective review includes four representative patients who underwent an endoscopic endonasal approach for the removal of lesions. RESULTS Based on the exposure provided by the endoscopic endonasal approach with a transmaxillary and transphenoidal approach using the 0- and 30-degree 4-mm nasal endoscope, the strut is trapezoidal in shape in cadaveric specimens. In all 100 dry skulls studied, the maxillary strut was present bilaterally. Measured by calipers (mean 6 SEM), the anteroposterior length of the strut averaged 4.18 mm on the right and 3.90 mm on the left. With CT imaging, the averages were 5.25 mm for the cross-sectional area of the strut and 4.43 mm in thickness. Clinical Series This retrospective series of four patients highlights the anatomical considerations of using an endoscopic endonasal approach. Case 1. When this 53-year-old presented with nasal obstruction and epistaxis, imaging showed a large lesion occupying the nasal cavity, sphenoid sinus, and adjacent to but not invading the anterior cranial fossa. An endoscopic biopsy was inconclusive. Endoscopic resection was successful and revealed a squamous cell carcinoma. Six 1740

3 Fig. 2. Endoscopic endonasal dissection of the left pterygopalatine fossa. A) Dissection of the infraorbital nerve to the inferior orbital fissure and then the foramen rotundum. B) Identification of the maxillary strut between the superior orbital fissure and the foramen rotundum. Drilling the maxillary strut gains access to the dura (C) and temporal lobe (D). FR 5 foramen rotundum; ICA 5 internal carotid artery; ION 5 infraorbital nerve; MS 5 maxillary strut; SPA 5 sphenopalatine artery; SS 5 sphenoid sinus. months after radiation, the tumor recurred in the pterygopalatine fossa, extending posteriorly to the foramen rotundum. Planning an endoscopic endonasal resection of the residual growing tumor, the maxillary sinus was accessed and the posterior wall was removed with margin, allowing access to the pterygopalatine fossa and the residual lesion. Tumor resection progressed smoothly by following the tumor to the middle fossa floor at the foramen rotundum. There the maxillary strut was drilled to expose the intracranial component of the tumor along V2, permitting a gross total resection. The patient tolerated the procedure without complications, and a postoperative PET scan revealed no residual disease. The patient had numbness in the distribution of V2, postoperatively related to resection of the nerve (Fig. 3A). Case 2. When this 31-year-old woman presented with a several month history of left facial pain, computed tomography revealed an expansile lesion involving the left pterygopalatine fossa and petrous apex. By endoscopy via a transmaxillary and transsphenoidal route, V2 was visualized and followed back to the foramen rotundum. Drilling the maxillary strut provided access to the middle fossa and revealed abnormal bone. Pathology was consistent with a benign bone cyst. The patient tolerated surgery without complications, but had numbness in the distribution of V2 due to resection of the nerve. Case 3. A 49-year-old man presented with a recurrent T4 squamous-cell carcinoma that involved the lateral nasal cavity wall at the posterior maxillary sinus, invading the medial wall of the posterior maxillary sinus and the pterygopalatine fossa with obvious perineural invasion of the inferior orbital nerve posteriorly toward the foramen rotundum and second branch of the trigeminal nerve. The patient underwent resection with positive margin at V2 extending into Meckel s cave (Fig 3B). Five days after surgery, when a delayed cerebrospinal fluid (CSF) leak occurred, imaging revealed significant pneumocephalus. The CSF leak was repaired using a combined endoscopic and transcranial approach. After receiving adjuvant radiation for a positive margin at Meckel s cave, the patient is recurrence-free at 18 months. V2 was functional and intact at the most recent follow-up examination. Case 4. When this 84-year-old woman presented with progressive right visual loss, imaging revealed a lesion arising from the foramen rotundum on the right, expanding into the SOF and compressing the optic nerve. It was located just posterior to the pterygopalatine fossa and anterior to the cavernous sinus. With the decision to resect this lesion endoscopically and decompress the optic nerve, the endoscopic endonasal exposure of the sphenoid and maxillary sinuses to access the pterygopalatine fossa yielded excellent tumor exposure (Fig. 3C). The lesion was then resected to its origin at the foramen rotundum. At this point, the maxillary strut was drilled to give access to the middle fossa and achieve gross total resection. The optic nerve was then decompressed endoscopically to maximize the potential for recovery of the patient s vision. Pathology was consistent with a V2 schwannoma. Owing to resection of V2, the patient has numbness in the distribution of the nerve. DISCUSSION Rhoton introduced the term maxillary strut to define the strut of bone separating the SOF from the foramen rotundum. 23 In our study, the maxillary strut was a trapezoid-shaped bone that separates the embryological foramen lacerum anterius into the SOF and the 1741

4 FR. Formation of the maxillary strut is usually completed between weeks 12 to 16 during gestation. 24 However, literature related to the maxillary strut is sparse. 23,25,26 Noting the presence of the maxillary strut bilaterally in all skulls, we propose that this structure serves as a reliable landmark for endoscopic endonasal approaches to lesions in the anterior and medial regions of the middle fossa. This includes lesions that arise in the pterygopalatine fossa, infratemporal fossa, foramen ovale and rotundum, cavernous sinus, ICA, and dura surrounding the temporal lobes. The lesions in this region can vary greatly, from T4 invasive tumors of the maxillary sinus with extension into the pterygopalatine fossa and foramen rotundum to neurilemmomas of the lower cranial nerves or sympathetic chain and parasellar tumors (e.g., chordomas, meningiomas). In our patients, the foramen rotundum and SOF functioned as corridors for tumor extension from the pterygopalatine fossa, infratemporal fossa, and maxillary sinus to the middle fossa and vice versa. Although a small structure, the strut was reliably present and easily identified in the dry skulls. Improved understanding of the anatomy in this region can enable safe removal of the maxillary strut, providing improved exposure for tumor resection. However, the close proximity of the strut to the temporal lobe dura requires careful removal with a high-speed diamond drill under continuous irrigation. Furthermore, judicious use of bipolar cautery is recommended because thermal spread can damage the dura and lead to an intraoperative or delayed CSF leak, as demonstrated in patient 3. Many studies have detailed the anatomy of this region; most studies excluded the importance of the maxillary strut. For example, in studying the anatomic landmarks in the pterygopalatine fossa, including the vascular anatomy and V2 and its course to the foramen rotundum, Sandu et al. do not mention the maxillary strut. 27 Noting its consistency in this region, we addressed the previous studies that noted the lack of familiar landmarks for expanded endonasal approaches. While others 15,27,28 noted useful landmarks, such as the vidian canal and lateral pterygoid plate, we propose that the maxillary strut can be added to the list of distinct and consistently present landmarks. CONCLUSION The expanded endoscopic endonasal approach is increasingly used for a variety of pathologies. Understanding the anatomy of the maxillary strut allows for its exposure and safe removal, which provides access to the anterior and middle fossa. As a surgical landmark, it can expand the utility of the endoscopic approaches for lesions originating from the pterygopalatine fossa, infratemporal fossa, and maxillary sinus that extend into the middle fossa. Fig. 3. Endoscopic endonasal resections of patients in case series. A) Left-sided resection of squamous cell carcinoma illustrating the foramen rotundum, sphenoid sinus, pterygoid buttress, and vidian nerve. B) Left-sided resection of squamous cell carcinoma showing the expanded foramen rotundum and pterygoid buttress. C) Right-sided view showing a V2 schwannoma with an expanded foramen rotundum. FR 5 foramen rotundum; PtB 5 pterygoid buttress; SS 5 sphenoid sinus; VC 5 vidian canal. 1742

5 BIBLIOGRAPHY 1. Al-Nashar IS, Carrau RL, Herrera A, Snyderman CH. Endoscopic transnasal transpterygopalatine fossa approach to the lateral recess of the sphenoid sinus. Laryngoscope 2004;114: Anand VK, Schwartz TH. Practical Endoscopic Skull Base Surgery. San Diego, CA: Plural Publishing; Burkart CM, Theodosopoulos PV, Keller JT, Zimmer LA. Endoscopic transnasal approach to the clivus: a radiographic anatomical study. Laryngoscope 2009;119: Cavallo LM, Cappabianca P, Galzio R, Iaconetta G, de Divitiis E, Tschabitscher M. Endoscopic transnasal approach to the cavernous sinus versus transcranial route: anatomic study. Neurosurgery 2005; 56(suppl): Cavallo LM, Messina A, Gardner P, et al. Extended endoscopic endonasal approach to the pterygopalatine fossa: anatomical study and clinical considerations. Neurosurg Focus 2005;19:E5. 6. de Divitiis E, Cappabianca P, Cavallo LM. Endoscopic transsphenoidal approach: adaptability of the procedure to different sellar lesions. Neurosurgery 2002;51: Jho HD, Ha HG. Endoscopic endonasal skull base surgery: Part 1 The midline anterior fossa skull base. Minim Invasive Neurosurg 2004;47: Kassam AB, Gardner P, Snyderman C, Mintz A, Carrau R. 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 2005;19:E6. 9. Kassam AB, Snyderman C, Gardner P, Carrau R, Spiro R. The expanded endonasal approach: a fully endoscopic transnasal approach and resection of the odontoid process: technical case report. Neurosurgery 2005; 57(suppl 1):E213 (abstract). 10. Laufer I, Anand VK, Schwartz TH. Endoscopic, endonasal extended transsphenoidal, transplanum transtuberculum approach for resection of suprasellar lesions. J Neurosurg 2007;106: Schwartz TH, Fraser JF, Brown S, Tabaee A, Kacker A, Anand VK. Endoscopic cranial base surgery: classification of operative approaches. Neurosurgery 2008;62: Stamm AC, Pignatari SSN, Vellutini E. Transnasal endoscopic surgical approaches to the clivus. Otolaryngol Clin North Am 2006;39: Alfieri A, Jho H-D, Schettino R, Tschabitscher M. Endoscopic endonasal approach to the pterygopalatine fossa: anatomic study. Neurosurgery 2003;52: Magro F, Solari D, Cavallo LM, et al. The endoscopic endonasal approach to the lateral recess of the sphenoid sinus via the pterygopalatine fossa: Comparison of endoscopic and radiological landmarks. Neurosurgery 2006;59(suppl 2):ONS237 ONS Fortes FSG, Sennes LU, Carrau RL, et al. Endoscopic anatomy of the pterygopalatine fossa and the transpterygoid approach: Development of a surgical instruction model. Laryngoscope 2008;118: Budrovich R, Saetti R. Microscopic and endoscopic ligature of the sphenopalatine artery. Laryngoscope 1992;102: Kassam AB, Prevedello DM, Carrau RL, et al. The front door to meckel s cave: an anteromedial corridor via expanded endoscopic endonasal approach- technical considerations and clinical series. Neurosurgery 2009;64(suppl 3):ONS71 ONS Theodosopoulos PV, Guthikonda B, Brescia A, Keller JT, Zimmer LA. Endoscopic approach to the infratemporal fossa: anatomic study. Neurosurgery 2010;66: Ginsberg LE. Imaging of perineural tumor spread in head and neck cancer. Semin Ultrasound CT MR 1999;20: Nemzek WR, Hecht S, Gandour-Edwards R, Donald P, McKennan K. Perineural spread of head and neck tumors: how accurate is MR imaging? AJNR Am J Neuroradiol 1998;19: Gandhi D, Gujar S, Mukherji SK. Magnetic resonance imaging of perineural spread of head and neck malignancies. Top Magn Reson Imaging 2004;15: Sanan A, Aziz KM, Janjua RM, van Loveren HR, Keller JT. Colored silicone injection for use in neurosurgical dissections: anatomic technical note. Neurosurgery 1999;45: Seoane E, Rhoton AL, de Oliveira E. Microsurgical anatomy of the dural collar (carotid collar) and rings around the clinoid segment of the internal carotid artery. Neurosurgery 1998;42: Shapiro R, Robinson F. The foramina of the middle fossa: a phylogenetic, anatomic and pathologic study. Am J Roentgenol Radium Ther Nucl Med 1967;101: Dallan I, Castelnuovo P, de Notaris M, et al. Endoscopic endonasal anatomy of superior orbital fissure and orbital apex regions: critical considerations for clinical applications. Eur Arch Otorhinolaryngol 2013;270: Laws E, Sheehan J. Sellar and Parasellar Tumors: Diagnosis, Treatment and Outcomes. New York, NY: Thieme; Sandu K, Monnier P, Pasche P. Anatomical landmarks for transnasal endoscopic skull base surgery. Eur Arch Otorhinolaryngol 2011;269: Snyderman CH, Pant H, Carrau RL, Prevedello D, Gardner P, Kassam AB. What are the limits of endoscopic sinus surgery? the expanded endonasal approach to the skull base. Keio J Med 2009;58: