Pupil-sparing third cranial nerve palsy with aberrant regeneration secondary to cavernous sinus arachnoid cyst.

A 66 year-old woman presented with a pupil-sparing partial third cranial nerve palsy with aberrant regeneration. Imaging revealed a cystic lesion in the right cavernous sinus, demonstrating signal characteristics consistent with arachnoid cyst. Oculomotor synkinesis and a pupil-sparing third cranial nerve palsy from an arachnoid cyst of the cavernous sinus have not been previously reported. Intracavernous arachnoid cysts are in the differential diagnosis of cranial nerve III palsies, with and without synkinesis or pupil involvement.