Acromegaly due to an ectopic pituitary adenoma in the clivus: case report and review of literature

Pituitary adenomas rarely originate outside the sella turcica. Ectopic locations include the suprasellar region, sphenoid sinus, cavernous sinus and clivus. We describe a 50-year-old female who presented with clinical signs and biochemical evidence of acromegaly. Pituitary MRI demonstrated a 2 mm hypointense lesion on the right side of the pituitary gland. However upon drilling of the upper clival bone to expose the sella during endoscopic transsphenoidal surgery, soft tumor-like tissue was encountered within the clivus. Exploration of the sella, including the area of hypointensity noted on preoperative imaging, did not identify any other abnormality. Immunohistochemical examination of the fully resected tumor demonstrated growth hormone immunoreactivity. Failed preoperative diagnosis of this rare ectopic GH-producing tumor was compounded by the presence of a misleading pituitary abnormality consistent with a microadenoma. The epidemiology and pertinent literature of this uncommon condition is discussed.