14 Orbital Decompression, Optic Decompression, Supraorbital Approach, and Transorbital Approach

The sinonasal cavity can be used as a corridor toward the orbital cavity and the optic canal. In particular, the ethmoid complex and the maxillary sinus are adjacent to the medial and inferior orbital walls, respectively, while the optic canal can be reached at the junction between the lateral and superior walls of the sphenoid sinus. Consequently, transnasal endoscopic surgery is currently employed for performing orbital and optic decompression (mainly for Graves’ disease and posttraumatic optic neuropathy), ^{1 , 2} repair of some fractures of the orbital walls, ^{3 , 4} and resecting selected orbital tumors and skull base lesions that compress the optic nerve. ^{5 – 8} Additionally, transnasal endoscopic surgery is an excellent approach to drain subperiosteal and orbital abscesses resulting from complicated acute rhinosinusitis. ^{9 , 10}

This chapter includes the description of four procedures: orbital decompression, optic decompression, supraorbital approach, and transorbital approach.

Orbital decompression is indicated when intraorbital pressure increases (causing exophthalmos, strabismus, and/or diplopia) as a result of dysthyroidism (especially Graves’ disease) or infection (i.e., abscesses requiring surgical drainage), leading to impairment of the optic nerve function. The medial wall and the portion of the inferior one medial to the infraorbital nerve can be removed through a transnasal approach. Furthermore, periorbital incision and lysis of the intraorbital connective septa further decrease intraorbital pressure in cases of severe orbital hypertension.

Optic decompression is indicated when retrobulbar compressive optic neuropathy occurs as a consequence of trauma, dysthyroidism, or skull base tumors or tumor-like lesions (e.g., fibrous dysplasia). The main clinical manifestations leading to indicate an optic decompression are visual field/acuity impairment, dyschromatopsia, and alteration in visual evoked potentials. Decompression can be obtained by removing the medial wall of the optic canal, incising the optic periosteum, and sectioning the annulus of Zinn. While performing these maneuvers, particular attention should be paid to not damage the ophthalmic artery, which commonly runs in the inferomedial quadrant of the optic canal.

The transnasal supraorbital approach consists of a subperiosteal dissection along the inferior face of the orbital roof. This route can be adopted to address lesions or fluid collections (i.e., subperiosteal abscesses) located below the orbital roof or to expand the transcribriform or transplanum–transtuberculum approach in lesions with lateral extension. To reach the orbital roof via a subperiosteal plane, the ethmoidal arteries must be sectioned to have a full view of the dihedral corner between the lamina papyracea and the fovea ethmoidalis. Craniectomy of the lesser sphenoidal wing and removal of the optic strut are also possible through this approach, providing subtotal exposure of the paraclinoid tract of the internal carotid artery.

The transnasal transorbital approach allows access to the extraconal and intraconal compartments of the orbit passing through the periorbit. Removal of orbital tumors is usually performed by blunt dissection with the help of cottonoids gently pushed along the surface of the lesion; this minimizes the chance of injury to neurovascular structures. However, from cadaveric dissection aiming to acquire sound anatomical knowledge of the position and relationship of the most important orbital structures, it is suggested to meticulously remove the orbital fat and identify the nerves and vessels running within the orbit. The main landmarks guiding orbital dissection are the extrinsic orbital muscles, which can be adequately exposed by removing the extraconal fat. Schematically, three triangles between the skull base, the medial rectus muscle, the inferior rectus muscle, and the orbital floor can be identified to access the intraconal orbital content.

In recent years, transorbital endoscopic approaches through eyelid skin and/or conjunctiva are gaining increasing popularity. ¹¹ – ¹⁵ Although the step-by-step description of these techniques (i.e., superior eyelid crease approach, precaruncular approach, preseptal lower eyelid approach, and lateral retrocanthal approach) is beyond the purposes of the present atlas, it is of note that transorbital endoscopic approaches are progressively included in the toolkit of skull base surgeons, thus warranting dedicated study and training. Therefore, the reader is strongly recommended to acquire familiarity with these approaches and use a cadaver dissection setting to compare the different degrees of maneuverability and exposure provided by endoscopic transnasal and transconjunctival/transcutaneous transorbital approaches when targeting orbital compartments and related skull base areas.

Related posts:

1 Classification of Endoscopic Transnasal Approaches to the Skull Base and Adjacent Areas 9 Transsellar Approach 10 Transsellar Transdorsal Approach 17 Medial Transcavernous Approach 18 Lateral Transcavernous Approach 21 The Suprapetrous (Meckel’s Cave) Approach

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