Ectopic cervical thymoma: a mimic of T-lymphoblastic lymphoma.

Ectopic cervical thymoma is a rare tumor that probably arises from ectopic thymic tissue trapped during migration of thymic primordia in the embryonic stage. To the best of our knowledge, only 20 cases have been reported. Our patient was a 68-year-old woman who had been suffering from a nodular lesion in the anterior neck for several years. She underwent nearly total right thyroidectomy. Eight years and nine months after surgery, she is free of tumor recurrence or metastasis. The tumor was nodular with fibrous septa, and was composed of varying numbers of epithelial cells and lymphocytes, corresponding to AB thymoma as classified by WHO. Using lymphoid markers only, it was initially misdiagnosed as T-lymphoblastic lymphoma. The lymphocytes expressed T-cell antigens and terminal deoxynucleotidyl transferase and exhibited high proliferation fraction. Awareness of ectopic cervical thymoma, careful microscopic examination, and a proper selection of antibodies for immunohistochemistry will lead to the correct diagnosis.