Sistrunk 法で切除した甲状舌管癌例

Thyroglossal duct cyst is a benign cystic disease that arises from remnants of the thyroglossal duct during fetal life, but it rarely shows malignant transformation. In most reported cases, thyroglossal duct carcinoma was diagnosed by postoperative histopathology after surgery for thyroglossal duct cysts that were considered benign prior to the surgery. The rate of correct diagnosis by preoperative puncture aspiration cytology is also only about 50%–55%. We report a case in which we were able to diagnose carcinoma of the thyroglossal duct by preoperative aspiration cytology. A 55-year-old man visited our hospital with the chief complaint of a painless anterior cervical mass that had been present for six months. Ultrasonography revealed an irregularly shaped hypoechoic tumor with a mixture of cysts and solid components, and calcification around the hyoid bone. The tumor was located close to the tip of the pyramidal lobe. Aspiration cytology suggested the diagnosis of papillary carcinoma. We performed Sistrunk surgery with additional neck dissection of the submental area and prelaryngeal area. There was no recurrence of the tumor until the end of 5-year follow-up period. The postoperative histopathology showed papillary carcinoma with cysts lined by striated columnar epithelium and squamous epithelium, which are components of the thyroglossal duct cyst, based on which we made the diagnosis of thyroglossal duct carcinoma. Extracystic infiltration was noted, and lymph node metastasis was found in the submental area and prelaryngeal area. When planning surgery for a thyroglossal duct cyst, the possibility of thyroglossal duct carcinoma should be considered. Malignancy should be suspected in the presence of thickening or irregularity of the cyst wall, solid lesions within the cyst, and/or calcified lesions. If extension outside the cyst wall is suspected, it is necessary to select a surgical procedure considering the possibility of lymph node metastasis.