Clival Ectopic Pituitary Adenoma Mimicking a Chordoma: Case Report and Review of the Literature.

Background. Purely ectopic pituitary adenomas are exceedingly rare. Here we report on a patient that presented with an incidental clival mass thought to be a chordoma. Endonasal resection, tumor pathology, and endocrinology workup revealed a prolactinoma. Case Presentation. A 41-year-old male presented with an incidental clival lesion presumed to be a chordoma. On MRI it involved the entire clivus, extended laterally to the petroclival junction, and invaded the cavernous sinuses bilaterally, encasing both internal carotid arteries, without direct extension into the sella. Intraoperatively, it was clear that the tumor originated from the clivus and that the sellar dura was completely intact. Frozen-section pathology was consistent with a pituitary adenoma. Immunostaining was positive for synaptophysin and prolactin with a low Ki-67 index, suggestive of a prolactinoma. Additional immunohistochemical stains seen in chordomas (EMA, S100, and Brachyury) and other metastatic tumors were negative. A postoperative endocrine workup revealed an elevated serum prolactin of 881.3 ng/mL (normal < 20). Conclusions. In conclusion, it is crucial to maintain an extensive differential diagnosis when evaluating a patient with a clival lesion. Ectopic clival pituitary adenomas, although rare, may warrant an endocrinological workup preoperatively as the majority may respond to medical treatment.