Ectopic cervical thymoma: a report of two cases of a rare entity frequently misdiagnosed on fine needle aspiration cytology and frozen section.

Ectopic cervical thymoma (ECT) is a rare tumor that is frequently misdiagnosed on fine needle aspiration cytology and frozen section. Using conventional light microscopy and immunohistochemistry, we characterized the only two cases of ECT found in our institutional files over a period of 20 years. Both tumors were classified as type AB-thymoma. Neoplastic cells expressed cytokeratins but not CD5. Non-neoplastic T-lymphocytes were positive for CD3 and CD5. Lymphocytes expressed CD1a in only one case. One tumor breached the capsule and had positive surgical margins. For this patient, adjuvant radiotherapy was given. The other patient has had an uneventful follow-up for 20 years with no other therapy than surgery. Both cases of ECT showed identical histomorphological and immunohistochemical features of type AB-thymomas originating in the thymus. Short follow-up precludes conclusion on the implication of positive margins in conjunction with adjuvant radiotherapy for one of the patients presented herein.