Ectopic primary intrathyroidal thymoma: a clinicopathological and immunohistochemical analysis of 3 cases.

Thymomas are rare tumors that occasionally arise from ectopic locations. Ectopic thymomas originating within the thyroid gland are an exceedingly uncommon clinical entity that has only been described sporadically. In this study, we present the clinicopathological and immunohistochemical features of 3 primary intrathyroidal thymomas. The patients were 2 women and 1 man between the ages of 43 and 53 years (average, 48 years). Clinically, the patients presented with neck pain or enlarged thyroid glands. Physical examination and thyroid ultrasound revealed the presence of nodular masses confined to the thyroid parenchyma. No concurrent mediastinal tumors were identified in any of the cases, and none of the patients had a history of thymoma. Fine needle aspirate performed in 1 case was interpreted as possibly Hashimoto thyroiditis. Surgical resection was performed in all cases. Grossly, the lesions were circumscribed masses measuring from 1 to 4 cm in size. Histologically, the lesions showed the classic biphasic cellular proliferation of thymomas characterized by varying proportions of epithelial cells and lymphocytes. Two patients remain alive and well 1.5 to 2 years after their surgical resection, whereas the third patient was lost to follow-up. The cases herein presented highlight an unusual tumor entity that can be clinically confused for more common lesions affecting the thyroid gland. Awareness of this entity is important to avoid misdiagnosis and secure appropriate clinical management.