FRI310 Massive Gonadotropin-Secreting Adenoma In A Young Man: A Challenging Differential Diagnosis Of A Sellar Mass

Disclosure: C. Nava Suarez: None. J. Prater: None. N. Blocher: None. S. Sathi: None. Introduction: Gonadotropin-secreting adenomas are usually nonfunctioning representing 90% of silent pituitary masses. However, functioning gonadotropin-secreting adenomas (FGA) are rare, with unknown incidence given their infrequent recognition. FGA usually presents with high FSH and variable sex hormone levels. Usually misdiagnosed, these tumors present with late mass effect symptoms. Neuroimaging usually shows a sellar mass with extrasellar extension and compression of nearby structures. We present a case of a man with a massive FGA with craniopharyngioma features on imaging. Case: A 33-year-old male with left eye blindness for 3 years presented for evaluation of acute headache and right eye blurriness but no other symptoms. Ophthalmologic evaluation demonstrated left optic atrophy, right optic disc edema, and temporal field cut from optic chiasm involvement. Hormonal workup showed a markedly elevated FSH at 36.8 mIU/ml (<12 mIU/ml), normal total testosterone at 835 ng/dL (250-1000 ng/dL), and mildly elevated prolactin at 28.6 ng/dL (<29.4 ng/dL), all other pituitary hormones were normal. Brain MRI demonstrated a multilobulated, heterogeneously enhancing solid-cystic mass in the sellar and suprasellar area. It was T1 iso-hypointense, T2/FLAIR isointense, and had a few calcifications. There was mass effect on the optic chiasm, left frontal and temporal lobes, and left lateral ventricle causing obstructive hydrocephalus. Craniopharyngioma was the initial diagnosis given radiographic features. The patient required an extended left frontotemporal craniotomy for tumor debulking. Pathology reported pituitary macroadenoma with positive FSH immunostaining. He is planned for radiation therapy given the presence of residual tumor. Discussion: This case illustrates the late presentation of gonadotrophin pituitary adenoma. Up to 90% of silent pituitary adenomas stain for FSH or LH, but are not clinically active. A minority of these secrete functioning hormones which can result in clinically relevant effects with FSH elevation more commonly seen than LH elevation. In our case one would have expected low testosterone in the setting of high FSH as seen in primary hypogonadism, but testosterone levels can range from low to high in FGA. Men usually complain of erectile dysfunction and decreased libido. Our case is particularly interesting because of the imaging features (mixed cystic-solid components with calcifications) suggestive of craniopharyngioma. Radiologic features have over 90% accuracy in distinguishing craniopharyngioma from pituitary adenomas. An accurate pre-operatively diagnosis is important as it may affect the surgical approach and prognosis. Clinicians should have a high level of suspicion for FGA in patients with neurological and visual symptoms, especially when associated with sexual dysfunction, although the last is not always present. Presentation: Friday, June 16, 2023