8203 A Solitary Fibrous Tumor Mimicking a Non-functional Pituitary Macroadenoma

Abstract Disclosure: L. Bernacet Rivera: None. S. Omay: None. A. Huttner: None. S.E. Inzucchi: None. Background: A solitary fibrous tumor (SFT), also known as hemangiopericytoma (HPC), is a rare subset of soft tissue tumors of mesenchymal origin. This type of tumor tends to have aggressive behavior and a high risk of recurrence. Approximately less than 1% of central nervous system (CNS) tumors have been identified as part of this subtype. Case Presentation: A 73-year-old female with medical history of primary hypothyroidism, myelodysplastic syndrome (MDS), and IgM kappa MGUS initially presented to her primary care physician for evaluation of progressive visual loss over several weeks, accompanied by worsening headaches. Ophthalmologic exam revealed bitemporal hemianopsia which prompted urgent imaging. Pituitary MRI with IV contrast revealed a solid sellar mass with suprasellar extension measuring 1.8 x 1.3 x 1.9 cm. The lesion was noted to superiorly displace the optic chiasm as well as to cause mild impingement of the anterior cerebral arteries. Patient was urgently referred to neurosurgery and endocrinology for further evaluation. Initial neuroendocrine laboratory assessment, performed at 8 am, revealed a cortisol 16.5 ug/dL, free T4 1.2 ng/dL, TSH 0.77 mIU/L, prolactin 9.9 ng/mL, IGF-1 17 ng/mL, the latter value consistent with adult growth hormone deficiency. Her LH and FSH were 4.3 mIU/mL and 12.6 mIU/mL, respectively, lower than expected for a post-menopausal woman. She underwent a transnasal transsphenoidal resection of the sellar lesion. Surgery was difficult due to the fibrous nature of the tumor, for which complete resection was not achieved. Post-operative course was complicated by thrombocytopenia due to MDS. Hormonal workup following surgery was consistent with central adrenal insufficiency, hypogonadotropic hypogonadism, and central hypothyroidism. Pathology showed densely cellular spindle cell neoplasm with a collagenous background consistent with hemangiopericytoma. She underwent fractionated radiotherapy and tumor has since remained stable in size. Her visual symptoms resolved quickly following surgery. Discussion: SFT is an aggressive mesenchymal tumor which rarely appears in the sellar region. There are no identified brain MRI findings that would suggest the nature of this tumor. As a result, endocrinologists should be aware of this rare condition while evaluating pituitary neoplasms. Presentation: 6/3/2024