Oculomotor Nerve Schwannoma Located in the Oculomotor Cistern

Background: OSs are extremely rare tumors, most often located in the interpeduncular cistern or the CS. We report an OS located predominantly within the oculomotor cistern, the arachnoid sac that surrounds the nerve for a short distance in the roof of the CS. We discuss a possible growth pattern for cavernous OSs.

Case Description: We report the case of a 34-year-old woman presenting with a right oculomotor nerve palsy. Magnetic resonance imaging revealed a mass within the borders of the roof of the CS extending forward toward the superior orbital fissure. A right pterional approach was undertaken, and the roof of the CS was opened just above the oculomotor nerve toward the superior orbital fissure. Although the part of the OS inside the oculomotor cistern was excised completely while preserving the anatomical continuity of the nerve, a subtotal removal was performed for the more anterior part of the tumor toward the superior orbital fissure. At 5 months follow-up, her third nerve paresis had improved dramatically.

Conclusions: Resection of cavernous OSs within the oculomotor cistern, where the third nerve is clearly separated from the adjacent neurovascular structures, is feasible with functional preservation of the nerve. The chance of occurrence of the nerve palsy may increase as the resection proceeds more anteriorly toward the superior orbital fissure.