What was the cause of third nerve palsy in our case? One possibility is that it was related not to the tumor but to the patient's underlying vascular disease. This would be consistent with the painless onset of the palsy and its complete resolution after about 7 months, although this is somewhat longer than one would expect in such a setting. Although lesions of the sphenoid sinus do not commonly produce third nerve palsies, a few such examples have been reported.5,6 Thus, the mass could have affected the oculomotor nerve in the anterior cavernous sinus by compression, by producing an inflammatory reaction, or by causing focal ischemia. Any of these mechanisms could account for the rapid resolution of the palsy following resection of the lesion. In any event, this case provides support for the recommendation that a patient with an isolated, complete, pupil-sparing OMNP be evaluated with neuroimaging when there is no evidence of improvement after several months.