Incidental High-Grade Sellar Solitary Fibrous Tumor Mimicking Non-Functioning Pituitary Adenoma: A Case Report and Literature Review.

BACKGROUND Sellar solitary fibrous tumors (SFT) are uncommon brain tumors belonging to the fibroblastic and myofibroblastic category of the 2021 World Health Organization (WHO) Classification of Central Nervous System (CNS) Tumors. Twenty-two instances of sellar WHO grade II and III SFT (SFT II/III) have been reported since 1983. SFTs II/III clinical and imaging findings resemble non-functioning pituitary adenomas (NFPAs). We report a 62-year-old woman with encephalopathy and an incidental WHO grade III sellar SFT presenting as a non-functioning pituitary mass. CASE REPORT A 62-year-old woman with encephalopathy and urosepsis was transferred for evaluation of an incidentally detected sellar mass. An endocrine workup was unremarkable and a presumed diagnosis of NFPA was made. A partial adenectomy was then performed through a trans-nasal trans-sphenoidal approach. Pathological analysis revealed a mesenchymal neoplasm with haphazardly arranged spindled to epithelioid cells, collagenized background, tortuous vasculature, high mitotic index, and Signal Transducer and Activator of Transcription 6 (STAT6) positivity. According to the 2016 CNS WHO guidelines, the diagnosis was an anaplastic hemangiopericytoma WHO grade III, now termed an SFT under the 2021 CNS WHO guidelines. Proton therapy to the dose of 59.4 gray given in 33 fractions was implemented adjuvantly. The residual tumor demonstrated shrinkage 1.5 years after proton therapy, and absence of recurrent disease after 3 years. CONCLUSIONS Sellar SFTs II/III can present as incidentalomas and be considered in the differential diagnosis of sellar masses. While some cause symptoms by local expansion mimicking NFPA presentations, local invasion and metastasis are reported. Surgical excision and pathologic confirmation guide management.