26 - Orbital Apex Surgery and Tumor Removal

Abstract

The orbital apex is a small, cone-shaped region located between the posterior ethmoidal foramen anteriorly, and the openings of the optic canal and superior orbital fissure posteriorly. It contains many critical neurovascular structures, such as the optic, oculomotor, abducens, and ophthalmic branch of the trigeminal nerve, along with the cavernous sinus, carotid artery, and periarterial sympathetic plexus. At this level extraocular muscles attach to the annulus of Zinn, a fibrous ring that surrounds the optic canal and the inferior part of the superior orbital fissure. Lesions in the orbital apex are rare, and they usually produce symptoms such as visual acuity reduction, extraocular muscle impairment with diplopia, pain, and exophthalmos. The differential diagnosis is broad and includes inflammatory, infectious, traumatic, vascular, and neoplastic causes. External surgical approaches to the orbit are well established. External orbitotomies can be performed with or without osteotomy and, in cases of more extensive tumors, the orbitozygomatic craniotomy offers a wide exposure of the orbital contents. However, medial and inferior orbital lesions are the most difficult to reach and are usually addressed via a transcutaneous or transconjunctival medial orbitotomy. These approaches are demanding for posterior tumors, because the cone-shaped surgical field is narrow and damage to neural, muscular, or vascular structures of the orbit can have serious consequences. For intraconal lesions, a temporary section of the medial rectus muscle and retraction of the globe can be required. Reports of endoscopic transnasal approaches to the orbit have been frequently published during the past several years, so endoscopic orbital surgery can now be considered as an alternative option to traditional external approaches in the management of selected orbital lesions.