Inflammatory Myofibroblastic Tumor of Thyroid Gland: A Case Report

Introduction. Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm characterized by differentiated myofibroblastic spindle cells accompanied by an inflammatory infiltrate of plasma cells and lymphocytes. While typically localized in the lungs, its primary manifestation within the thyroid gland is exceptionally rare, posing significant diagnostic challenges due to its ability to mimic aggressive thyroid malignancies on clinical and radiological assessments. Case Report. A 48-year-old female healthcare professional with a history of a benign contralateral thyroid lobectomy 10 years prior presented with a painless left neck swelling. Ultrasonography revealed a 40 × 22 mm solid, hypoechoic, lobulated nodule (TI-RADS 4). Following the 5-month observation period, the lesion exhibited rapid dimensional growth to 47 × 27 mm and demonstrated severe stiffness on shear-wave elastography. Considering the American Thyroid Association guideline criteria and clinical concern, completion thyroidectomy was performed. Histopathological examination and immunohistochemical analysis revealed a neoplastic spindle cell proliferation that was diffusely positive for smooth muscle actin (SMA) but completely negative for anaplastic lymphoma kinase-1 (ALK-1) and thyroid transcription factor-1 (TTF-1), establishing a definitive diagnosis of primary thyroid IMT. No recurrence was observed during the 1-year follow-up. Conclusion. Primary thyroid IMT is a unique entity that should be considered in the differential diagnosis of rare spindle cell thyroid lesions. Definitive diagnosis relies on postoperative histopathological and immunohistochemical characterization rather than preoperative biopsy alone.