Optic nerve sheath fenestration: a revised lateral approach for nerve access

Abstract

Idiopathic intracranial hypertension (IIH), also known as pseudotumor cerebri, describes a disease of poorly understood pathophysiology with a specific set of signs and symptoms including potentially irreversible and blinding visual loss. Optic nerve sheath fenestration (ONSF) is a well-described surgical treatment for patients with IIH and progressive visual loss despite maximally tolerated medical therapy. A number of optic nerve access procedures have been described including medial transconjunctival, superomedial lid crease, and lateral orbitotomy with and without bone takedown. The purpose of this report is to describe a revised lateral approach for temporal optic nerve access that obviates the need to traverse through the intraconal fat of the central surgical space in the previously described lateral approach techniques.

Keywords: Idiopathic intracranial hypertension; lateral orbitotomy; optic nerve sheath fenestration; pseudotumor cerebri.

Figure 1.

Axial cut through the mid-orbit demonstrating the 3 previously reported approaches to the optic nerve (dashed lines) as well as the revised lateral approach (solid line).

Figure 2.

The revised lateral approach begins with a small lateral canthotomy without cantholysis (A). The conjunctiva and Tenon’s is then elevated and divided in continuation with the canthotomy (B). Care is taken to avoid damage to the insertion of the lateral rectus muscle which is isolated on a muscle hook after the lateral quadrants have been cleared with Stevens scissors in the manner of an enucleation procedure (C).

Figure 3.

Blunt dissection with thin, narrow malleable retractors along the episcleral surface in the superotemporal quadrant above the lateral rectus is used to reach the posterior globe. Dry 1⁄2” neurosurgical cottonoids are used to retract the fat and aid visualization (A). With the pupil as a reference point, the optic nerve sheath is easily located (B).

Figure 4.

Schematic diagram representing manipulation and fenestration of the optic nerve sheath. Beginning at top-left, the dura and arachnoid are grasped together with forceps perpendicular to the axis of the optic nerve. The dura and arachnoid are incised with microsurgical scissors until a fluid gush is observed (top-right). Vertical back cuts are then made in parallel with the axis of the optic nerve and the sheath window is then amputated transversely at its posterior base (bottom-right).