Cavernous malformations (CMs) arising intrinsically to the cisternal segment of the trochlear nerve are extremely rare. This case of a trochlear nerve cavernous angioma is the third to be reported in the neurosurgical literature and the first to be resected by a middle fossa approach.
The authors present a case of a 31-year-old woman with progressive left-sided headache and left hemisensory symptoms, whose magnetic resonance imaging showed a solid enhancing tumor in the left ambient cistern at the level of the midbrain-pontine junction causing significant brainstem compression. Intraoperatively, a left trochlear nerve cavernous angioma circumferentially enveloping the nerve was visualized. The angioma was microsurgically resected by a middle fossa approach under frameless stereotactic guidance. Gross total resection of the intrinsic trochlear nerve lesion was achieved, although the trochlear nerve could not be preserved intact.
CMs should be considered in a possible differential diagnosis of cisternal trochlear nerve tumors. Surgical resection remains the standard of care, and is indicated for relief of compressive symptoms and prevention of future bleeds. Postoperative diplopia often persists; however, resolution of diplopia reported in the literature can be attributed to either regeneration after direct surgical repair of the sacrificed nerve or a spontaneous adaptation over time.
