PSUN343 Ectopic Prolactinoma in the Bony Clivus: A Common Disease in an Uncommon Location

INTRODUCTION: Ectopic prolactinoma has previously been reported and may be found in various locations, including sphenoid sinus, cavernous sinus, suprasellar region, nasopharynx, and rarely the clivus. We report a case of prolactinoma without any evidence of adenoma in the pituitary, which was subsequently found to be located to be in the bony clivus, after 36 years of initial presentation. CASE DESCRIPTION: A 66-year-old woman was seen in the clinic for known history of hyperprolactinemia. She was first diagnosed at the age of 30 when she presented with headaches, irregular menstrual cycles, and galactorrhea. MRI Pituitary at that time was not suggestive of a pituitary adenoma. She was thought to have a microadenoma not visualized on imaging and was only treated with dopamine agonist therapy for 2-3 years at that time. Presently, she complained of mild headaches intermittently but denied any symptoms of galactorrhea. Physical examination, including visual field testing, was unremarkable. Lab tests were suggestive of elevated prolactin levels, which had increased to 171ng/ml as compared to 121 ng/ml a year ago (RR: 3.3- 26.7 ng/ml). Chemistry panel, thyroid function test were in the normal range. Given uptrending prolactin levels, MRI Pituitary was repeated, which showed normal pituitary gland for age, and an enhancing mass with intermediate T1 and T2 signal in the bony sella measuring 1.4×1.1×1.5 cm, previously measuring 1.3×1.1×1.2 cm (3y ago), with loss of the normal bony cortex abutting the pituitary gland. Pt subsequently underwent endoscopic transsphenoidal biopsy of the clival lesion. Histopathology and immunochemical staining results showed findings consistent with pituitary adenoma, prolactinoma. DISCUSSION: Ectopic pituitary tissue, as well as prolactinoma, have been reported at various locations along the migratory path of the pituitary gland. The craniopharyngeal canal, which provides the opening for oral ectoderm, which is also known as Rathke's pouch, to migrate superiorly into the sella, leaves a bony layer separating the intracranial sella turcica from the extracranial sinuses and nasopharynx. Growing mass in the bony sella, as seen in our patient, is concerning for several rare pathologies with malignant potential, hence requiring biopsy. Tumors of the clivus constitute less than 1% of all intracranial neoplasms- which include chordoma, lymphoma, metastatic carcinoma, chondrosarcoma, meningioma, craniopharyngioma, germ cell tumor, astrocytoma, and pituitary adenoma. Less than 15 cases of clival ectopic prolactinoma have been reported in the past. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.