The Medial Endoscopic Approach to the Orbit

15 The Medial Endoscopic Approach to the Orbit

M. Zoli, Thiago Albonette Felicio, D. A. Hardesty, Bradley A. Otto, Ricardo L. Carrau, and Daniel M. Prevedello

Abstract

Endoscopic endonasal resection of orbital intraconal retrobulbar lesions has gained popularity in last few years. In this region, knowledge of anatomy is paramount to orient and guide the surgeon. The aim of this chapter is to describe the anatomy of the orbit from the endoscopic endonasal perspective. Two surgical cases are reported to enlighten the advantages and limits of this approach. We also provided detailed description of the surgical technique, emphasizing the important anatomical landmarks with cadaveric dissection pictures.

At the end of the chapter, the reader will be able to select lesions that can be approach through this route, considering their location and relationship to key anatomical landmarks, thus maximizing its efficacy and reducing its morbidity.

Keywords: Keywords: EEA, medial orbital approach, endoscopic medial orbital approach

15.1 Introduction

Recently, few cases have been reported of endoscopic endonasal resection for orbital intraconal lesions.1 ^, ² ^, ³ ^, ⁴ ^, ⁵ ^, ⁶ ^, ⁷ ^, ⁸ ^, ⁹ ^, ¹⁰ ^, ¹¹ ^, ¹² ^, ¹³ ^, ¹⁴ ^, ¹⁵ ^, ¹⁶ This route was proposed by Sethi and Lau, who described in 1997 a series of six endoscopic endonasal biopsies for orbital apex lesions,¹⁰ while in 1999 Herman et al reported the first resection of an orbital cavernoma located inferomedial to the optic nerve.⁹ The orbit is one of the most complex regions of the skull base, and the anatomical knowledge of its structures, particularly the location and relationship of vessels and nerves, is crucial to orient the surgeon.¹⁷ The aim of this chapter is to describe the anatomy of the orbit and its contents from an endoscopic endonasal perspective, and to investigate the advantages and limits of this approach, utilizing cadaveric dissections. Two surgical cases are reported to enlighten the results of this approach.

15.2 Materials and Methods

Anatomical dissections of 12 orbits have been performed in six colored latex injected cadaveric specimens, simulating the endoscopic endonasal approach (EEA). Endonasal anatomical dissections were carried out using 0, 30, and 70 degrees rod lens endoscopes (Karl Storz, 4 mm in diameter, 18 cm in length, Hopkins II – Karl Storz Endoscopy-America, Inc., Culver City, CA) with a high-definition camera. We also provided pre- and postoperative images from two clinical case to illustrate the chapter.

15.3 Surgical Technique

The endoscopic endonasal dissection started with a middle turbinectomy followed by anterior and posterior ethmoidectomy and wide anterior sphenoidectomy to expose the posterior wall of sphenoid sinus and laterally the lamina papyracea ( Fig. 15.1a). The medial portion of the posterior wall of the maxillary sinus was resected to expose the posterior wall of the maxillary antrum and the vertical process of the palatine bone. The orbital apex was identified after localizing and following the optic nerve protuberance in the posterior wall of sphenoid sinus. With a 30 degrees optic, the lamina papyracea was easily fractured with a Cottle dissector; then it was detached from the orbital floor and roof with a Kerrison punch or simple traction and elevation ( Fig. 15.1b). The periorbita was therefore linearly incised starting from the orbital apex. Subsequently, the medial and inferior rectus and superior oblique muscles were identified from their insertion at the annulus of Zinn to the ocular bulb ( Fig. 15.2a). Considering the relationship of these three muscles, two triangles can be identified: one inferior between the inferior and medial rectus muscle and one superior between the medial rectus and the superior oblique ( Fig. 15.2b). Both these windows give access to the medial compartment of the entire retrobulbar space. After careful removal of the fat in the retrobulbar space, the contents of the medial compartment of the orbit, consisting the optic nerve, ciliary nerves, nasal division of the nasociliary nerve, the two divisions of the oculomotor nerve, ophthalmic artery and its main branches (anterior and posterior ethmoidal and central retina artery), and few highly variable venous vessels, can be identified. The perspective obtained passing through the inferior triangle is different from when passing through the superior. From the former window the inferolateral quadrant of the orbit and the apex are exposed. The main eloquent structures are located in the periphery of this work trajectory. Indeed, the inferior division of the cranial nerve (CN) III, which gives branches for the inferior rectus and inferior oblique muscles, passes at the orbit apex in the ventral surface of the former muscle, embedded, and thus protected, in it ( Fig. 15.2c). Similarly, the superior division of the CN III, which provides the innervation for the medial and superior rectus, runs from the apex embedded in the ventral surface of the medial rectus ( Fig. 15.2c). The optic nerve and the ophthalmic artery are identifiable and represent the lateral limit of this approach ( Fig. 15.3a). The ophthalmic artery gives off the ciliary arteries, which course surrounded by the long ciliary nerves (the former supply the eyeball and the latter, which are sympathetic nerves to dilator pupillae, derive from the ciliary portion of the nasociliary nerve). The vascular structures present in this compartment are medial branches of ophthalmic artery to the periorbita and muscles, such as the artery for inferior muscle, observed in all the specimens, which present a superoinferior direction in the posterior third of the retrobulbar space. Few inconstant venous structures, mostly tributaries of the superior orbital vein (different from the inferior orbital vein, which is formed on lateral orbital corner, the superior orbital vein receives its tributaries from the medial orbital corner and represents the main venous drainage of the orbit) are observed in this space. To enlarge the exposure of the medial compartment of the orbit superiorly, a gentle superior retraction of the medial rectus muscle can be necessary ( Fig. 15.3a). The superior triangle permits to identify the superomedial branches of the ophthalmic artery, mainly represented by the ethmoidal arteries ( Fig. 15.3b). In all our specimens these arteries originated independently by the ophthalmic artery in its superomedial surface. Through this window the bottom-up course of the nasal division of the nasociliary nerve (the only division of V1 passing through the annulus of Zinn, above the optic nerve) is similarly visualized. This nerve gives origin to the clearly visible anterior and posterior ethmoidal nerves in correspondence to the homonymous arteries ( Fig. 15.3b). At the orbital apex the CN VI and the ciliary division of the nasociliary nerve (the division occurs on the orbit apex) run deeply and laterally to optic nerve and thus are protected by their location from surgical injuries throughout this approach. Similarly, the frontal and lacrimal divisions of V1, which pass outside and superiorly to the annulus of Zinn, are protected by the superior rectus muscle, above which the frontal nerve runs, and by its lateral position, because the lacrimal nerve runs along with the lacrimal artery and vein toward the lacrimal gland in the anterosuperolateral corner of the orbit. The CN IV passes into the orbit outside the common tendon as well, and it is directed medially to run embedded in the inner surface of the superior oblique muscle. Thus, it could be considered as the superior limit of the EEA at the level of the apex and of the posterior third of the retrobulbar space. Extending anteriorly by removing the lacrimal and maxillary (partially) bones, the inferior oblique muscles and the terminal branches of the inferior division of the CN III reaching it are appreciable through angled optic (30, 45 and 70 degrees). At this level the lacrimal sac and duct are visible. The need of angled optic and angled instruments and the unfavorable trajectory make the access to this anterior part of the orbit highly demanding, but feasible, from the endoscopic endonasal route.

Fig. 15.1 Endoscopic endonasal cadaveric dissection. 30 degrees angled endoscope. Right Orbit. (a) The lamina papyracea is exposed after a posteroanterior ethmoidotomy and sphenoidotomy. (b) After the removal of the lamina papyracea using a Kerrison punch or retractor, the periorbita is exposed. The anterior ethmoidal artery is visible.

Fig. 15.2 Endoscopic endonasal cadaveric dissection. 30 degrees angled endoscope. Right Orbit. (a) After opening of the periorbita, the inferior and medial rectus and superior oblique muscles are visible. (b) After dissection of the muscles and removal of the periorbital fat, two triangular spaces can be identified (dotted lines), one superior, between medial rectus and superior oblique, and one inferior, between inferior and medial rectus. The inferior triangle gives access to the inferomedial quadrant of the orbit, while the superior to the upper part of the medial compartment. (c) The orbital apex is exposed. The optic nerve and ophthalmic artery are visible. Embedded in the inner surface of the medial and inferior rectus muscle, the two divisions of the CN III are appreciable. CN III divides into two division before entering the annulus of Zinn at the level of the superior optical fissure. A., artery; CN, cranial nerve; Inf. Div., inferior division of CN III; M., muscle; ON, optic nerve; Sup. Div., superior division of CN III.

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