A 68-year-old man had a rapidly growing, painless neck mass, thought to be nodular goiter. Ultrasonography showed a giant, heterogeneous mass occupying the middle and superior poles and protruding outside of the left thyroid lobe. The results of the thyroid function tests were normal. Thyroid scintigraphy revealed a large hypoactive nodule in the left thyroid lobe. Complete surgical removal of tumor was performed and macroscopically demonstrated a well-demarked lesion outside the thyroid gland. Microscopically, the lesion was composed of fibroblast-like spindle cells in a patternless architecture and extensive stromal hyalinization. Immunohistochemistry showed positive reaction for CD34 in spindle cells and diffuse bcl-2 staining. The pathology was confirmed as solitary fibrous tumor. In the follow-up period after surgery, thyroid scintigraphy showed normal left thyroid lobe. Solitary fibrous tumor originated from or associated with thyroid gland is extremely rare. According to our knowledge, this is the first reported solitary fibrous tumor presenting like a cold thyroid nodule. This pathology must be considered for differential diagnosis of neck masses in the thyroid region. 1. Introduction Solitary fibrous tumor (SFT) is a rare spindle cell neoplasm of mesenchymal origin that was first described in the pleura . Since then, SFT has been recognized in various sites other than the pleura, such as mediastinum, pericardium, and peritoneum [2–4]. Head and neck SFTs are exceedingly rare, and they were firstly described as a case report in 1991 . They were presented as asymptomatic slow-growing massess or with local symptoms due to compression. In most cases, complete surgical resection is the only appropriate treatment . Diagnosis is often difficult and not definite until morphologic or immunohistochemical evaluation. SFT arising from the thyroid gland is also uncommon. It was first described by Taccagni et al. in 1993 . Up to date and to the best of our knowledge, 23 cases of SFT in the thyroid gland have been reported in the literature, approximately all of them with benign characteristics [8–10], only 2 of them with malignant clinical features like local recurrence and metastasis . Here, we present the first reported SFT mimicking hypoactive thyroid nodule in thyroid scintigraphy. 2. Case Report A 68-year-old man presented with a 2-month history of a rapidly growing mass in the left neck on the thyroid gland region. He did not have any history of thyroid disease. He did not describe any symptoms like hoarseness, dyspnea, local pain, or
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