Rapidly-growing ectopic pituitary adenoma within the sphenoid sinus--case report.

A 75-year-old male with left abducens nerve paresis presented with an ectopic pituitary adenoma invading the posterior wall of the sphenoid sinus. The sphenoidal mass grew rapidly for 6 months with left ophthalmoplegia and was partially removed via the transsphenoidal approach. The histological examination showed a benign pituitary adenoma, but the MIB-1 proliferating cell index was 6.8%, reflecting the clinically malignant behavior. The symptom gradually improved without tumor regrowth over 1.5 years after conventional irradiation.