6672 Pituicytomas and Spindle Cell Oncocytomas: Rare Posterior Pituitary Tumors

Abstract Disclosure: Y. Park: None. A. Shen: None. M. Christie: None. J. Wentworth: None. C.J. Yates: None. J. King: None. Background: Pituicytomas and spindle cell oncocytomas (SCO) are rare non-functioning benign posterior pituitary tumors that can present as suprasellar or sellar-suprasellar masses.[1] Pituicytomas originate from the pituicytes in the neurohypophysis and infundibulum of the pituitary gland.2 SCO were previously thought to derive from the adenohypophysis,3 however, are now classified as a tumor of the neurohypophysis characterized by immunohistochemical reactivity to thyroid transcription factor 1 (TTF1).4 According to the World Health Organization 2021 classifications, pituicytomas, granular cell tumors and SCO may represent morphologic variations of the same tumor expressing TTF1.5 Due to their rarity, their clinical characteristics are not yet well-defined and can be mistaken as non-functioning pituitary adenomas. Methods: We retrospectively reviewed the clinical data of two patients with pituicytomas and two patients with SCO confirmed on histopathology at our institution, evaluating their clinical characteristics and management outcomes. Results: Two male patients, aged 59 and 79, were diagnosed with pituicytoma, and two male patients, aged 33 and 55 were diagnosed with SCO. Three presented with visual impairment from mass effects and three patients had hypogonadotropic hypogonadism. None had pre-operative arginine vasopressin (AVP) deficiency. All lesions were isointense on T1-weighted, and most were hyperintense on T2-weighted magnetic resonance imaging. Three cases had non-gross total resection due to hypervascularity. Postoperatively, two patients developed AVP deficiency and three developed persistent anterior pituitary insufficiency (Table 1). Pituicytomas had a Ki67 of 1-3%, and SCO had a Topoisomerase labelling index of <1%. In one case of pituicytoma, due to tumor recurrence 2 years after initial surgery, adjuvant radiotherapy was considered. However, the patient developed a severe peri-tumoral subarachnoid hemorrhage and died prior to receiving radiotherapy. In contrast, the progression of the residual SCO occurred at a slower rate. Discussions: Posterior pituitary tumor differentials are broad, including pituicytoma, SCO, granular cell tumor, craniopharyngioma, meningioma and germinoma;6 hence, histopathological diagnosis is crucial. Although benign, pituicytomas and SCO can result in increased morbidity and postoperative complications, such as AVP deficiency and hypopituitarism. Recurrence and progression are common.7, 8 Gross total resection is optimal, but this is difficult due to hypervascularity.9 Our case of peri-tumoral subarachnoid hemorrhage resulting in death emphasizes the hypervascular nature of pituicytomas. Patients with pituicytomas and SCO should be monitored for tumor progression or recurrence and hemorrhagic complications. Adjuvant radiotherapy may be considered for the management of tumor recurrence. Presentation: 6/3/2024