Solitary Fibrous Thyroid Tumor: A Case Report

Introduction: Solitary fibrous thyroid nodules are rare tumors and can mimic benign thyroid goiter and neoplasms. Case Description45 years old Caucasian female, with no significant past medical history, who presented to endocrinologyclinic for left neck mass evaluation. She denied previous history of thyroid disease, weight loss, cold/heatintolerance, menstrual irregularity, toxic or obstructive thyroid related symptoms. Her family history issignificant for maternal pancreatic cancer. Clinical exam was unremarkable except for left thyroid mass. An initial thyroid ultrasound showed left thyroid nodule 20 x16 x 25 mm in size five years prior topresentation. Repeated Fine Needle aspiration yielded benign follicular cells, histiocytes and fewlymphocytes. The nodule continued to increase in size reaching 46 mm in the long axis per thyroidultrasound at presentation to clinic. Her TSH, FT4 and total T3 remained within normal ranges. She wasreferred for surgical evaluation and underwent left thyroid lobectomy. Pathology reported 50 mm wellcircumscribed intrathyroidal neoplasm composed of spindle cells with pauci to moderate cellularity with noincreased mitotic activity, nuclear atypia, or necrosis. Immunohistochemistry was positive for STAT 6 andCD34and negative for PAX-8, TTF-1, S100 and SMA. The patient remains euthyroid with no lymph nodeor organ involvement after 5 years from initial presentation. Discussion: Solitary fibrous tumors (SFT) of the thyroid are rare although they have been described in differentanatomic sites (1). It presents as slow growing, painless, non toxic nodule in middle age of both sexes (1,2). The diagnosis of these tumors via FNA is difficult due to cellular paucity. Histologic findings may bechallenging due to shared features with other thyroid undifferentiated, papillary and follicular cancervariants. Immunohistochemistry are warranted to assist in confirmation-STAT6 and CD34 (3). SFT tumorsare mostly benign tumors and carries favorable prognosis. References: (1) Thompson, L.D.R., Wei, C., Rooper, L.M. et al. Thyroid Gland Solitary Fibrous Tumor: Report of 3 Cases and aComprehensive Review of the Literature. Head and Neck Pathol13, 597–605 (2019)(2) Ghasemi-Rad M, Wang KY, Jain S, Lincoln CM. Solitary fibrous tumor of thyroid: a case report with review ofliterature. Clin Imaging. 2019;53:105–107. doi: 10.1016/j.clinimag.2018.09.011.(3) Matoso A, Easley SE, Mangray S, Jacob R, DeLellis RA. Spindle cell foci in the thyroid gland: an immunohistochemicalanalysis. Appl Immunohistochem Mol Morphol. 2011;19(5):400–7.