Background: Primary synovial sarcoma (SS) of the thyroid (PSST) is extremely rare. Its differential diagnosis from other neoplasms is essential since it has different management protocols and prognosis. Case: A 26-year-old man with a 4.5-cm solid lobulated mass was seen at an outside hospital. Fine needle aspiration (FNA) was interpreted as a papillary carcinoma, and a total thyroidectomy was performed. The final histologic diagnosis was spindle epithelial tumor with thymus-like differentiation (SETTLE). No metastases were detected at that time, and the patient received radioactive iodine treatment. Two years post-surgery, he was seen at our hospital with a local recurrence, and FNA was considered as consistent with SETTLE. The mass was resected, and a left modified radical neck dissection was performed. The tumor revealed necrosis and a high mitotic index. Following histologic, immunohistochemical, and molecular studies, the tumor was classified as a PSST. The patient received chemotherapy and targeted immunotherapy, but he died 41 months after the initial presentation. Conclusion: The main diagnostic pitfall of PSST is SETTLE. The presence of mitotic figures and basal lamina material, negative staining for smooth muscle actin, and positive staining for transducer-like enhancer of split 1 antibody favor SS over SETTLE. SYT gene rearrangement is essential to establish the definitive diagnosis of PSST.
Acta Cytologica

中文翻译：

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甲状腺原发性滑膜肉瘤：细胞学诊断和文献复习中的挑战。

背景：甲状腺原发性滑膜肉瘤（SS）（PSST）极为罕见。由于它具有不同的治疗方案和预后，因此与其他肿瘤的鉴别诊断至关重要。案件：在一家室外医院看到一名26岁的男子，身体小叶质量为4.5厘米。细针穿刺术（FNA）被解释为乳头状癌，并进行了全甲状腺切除术。最终的组织学诊断为纺锤体上皮肿瘤，胸腺样分化（SETTLE）。当时未发现转移，患者接受了放射性碘治疗。手术两年后，他在我们医院被发现局部复发，FNA被认为与SETTLE一致。切除肿块，并进行左改良根治性颈清扫术。肿瘤显示坏死和高有丝分裂指数。经过组织学，免疫组织化学和分子学研究，将肿瘤分类为PSST。该患者接受了化疗和靶向免疫治疗，结论： PSST的主要诊断陷阱是SETTLE。有丝分裂图形和基底层材料的存在，平滑肌肌动蛋白的阴性染色和拆分1抗体的换能器样增强子的阳性染色都比SS更有利于SS。SYT基因重排对于建立PSST的明确诊断至关重要。
细胞学学报