39 Transcranial Orbital Approaches
Summary
Transcranial approaches afford circumferential access and visualization of the optic apparatus and serve an important role in the resection of mass lesions involving the optic nerve, especially those at the posterior third of the orbit, with intracranial extension, or with bilateral involvement. Transcranial approaches to the orbit may be conceived as a series of modular advancements, centered about the superior orbital rim, with stepwise expansion to the lateral orbital rim, zygoma, and frontotemporal calvarium. Selection of the operative approach is dictated by specific features of the lesion itself—location, extension outside the orbit, presumed pathology, vascular supply, and anticipated firmness are some important considerations. Additional concerns include existing neurologic symptoms and suspected neurovascular involvement, cosmetic considerations, and surgeon experience. Decompression of the anterior clinoid and optic canal are critical in preservation or restoration of vision in situations of optic nerve compression. Potential risks include postoperative periorbital swelling, temporary impairment of globe motility and extraocular movements, frontalis weakness, and enophthalmos or exophthalmos. Visual integrity is optimized with avoidance of intraoperative hypotension, rapid cerebrospinal fluid drainage, thermal injury from drilling or coagulation, and aggressive dissection around the optic apparatus.
The transcranial approach for intraorbital tumors and intracranial tumors with canalicular or intraorbital extension has been long pursued, as eloquently advocated by Walter Dandy. 1 Strikingly, Dandy noted that prevention of brain swelling through improvements in anesthesia allowed the size of the craniotomy to be greatly reduced and that a small bony opening was equally effective as a larger one. This astute observation of transosseous exposure of the lateral and superior orbit transformed circumferential access to the optic apparatus. In particular, Dandy advised the intracranial approach, for facile exploration and extirpation of tumor from any compartment of the orbit, especially those that extend posterior to the orbit.
39.1 Goals
To provide access to the entire orbit, especially the posterior third, and any lesions with intracranial extension (Fig. 39‑1).
To allow access to bilateral optic nerves with simultaneous access to the intraorbital and intracranial compartments.
To expose periorbita for exploration of infiltrating tumor.
Fig. 39.1 Axial T2 MRI of a right optic nerve sheath meningioma with invasion of the cavernous sinus and retrobulbar orbital space (demarcated by line), leading to proptosis.
39.2 Advantages
Wide access to the full length of the optic nerve, superior orbital fissure, and bony orbit.
Ability to address pathologies that span the cranio-orbital compartments.
Vascular control of the proximal ophthalmic system.
39.3 Expectations
Postoperative periorbital swelling and possible temporary paresis of extraocular movements, depending on the extent of periorbital violation and intraorbital dissection.
Possible frontalis weakness.
Possible enophthalmos or exophthalmos may result from intraorbital scarring and reconstruction.
39.4 Key Principles
Selection of the operative approach is dictated by lesion factors, including its location, pathology, vascular supply, and anticipated firmness; existing neurologic symptoms and suspected neurovascular involvement; cosmetic considerations; and surgeon experience. Transcranial approaches to the orbit may be conceived as a series of modular advancements, centered about the superior orbital rim, with stepwise expansion to the lateral orbital rim, zygoma, and frontotemporal calvarial vault (Fig. 39‑2). Additionally, the endoscope affords a complementary route to the medial and inferior orbit that may be considered for select pathologies as a primary modality or to augment the visualization around angles and critical neurovascular structures.
Orbital pathologies which span extraorbital compartments include meningiomas, gliomas, metastatic tumors, hemangiomas, fibrous dysplasia, tumors of the lacrimal gland, vascular malformations, and inflammatory conditions, among others. Of these, meningiomas are the most common and the most varied in their anatomic involvement. Anteriorly based tumors that involve the periorbita and orbit commonly present with proptosis and impairment of motility; posteriorly based tumors manifest classically with painless progressive visual loss. The presence of proptosis in a bone invasive meningioma mandates exploration of periorbita to excise invasive tumor, while visual loss should prompt exploration and decompression of the optic canal.
39.5 Indications
Exposure of lesions involving both the intraorbital and intracranial compartments.
Access to the posterior third of the orbit.
Access to bilateral optic nerves and the optic chiasm, including a long length of the optic nerve sheath.
When primary orbitotomy provides inadequate access to a lesion.
39.6 Contraindications
Anticipated poor healing with limited reconstructive options if a wide transcranial incision and exposure is performed.
Patient concerns regarding temporary or permanent cosmetic sequelae.
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