Ectopic Hamartomatous Thymoma: A Review Of The Literature With Report Of New Cases And Proposal Of A New Name: Biphenotypic Branchioma.

Ectopic hamartomatous thymoma (EHT) is a rare benign neoplasm of the lower neck suggesting branchial origin. Despite use of the term thymoma in the nomenclature, there is no evidence of thymic origin or differentiation. It affects middle-aged adults with a remarkable male predominance. To date less than 80 cases have been reported in the English literature. We present here two additional cases of EHT. The first is a benign case in a 31-year-old man, showing typical histological features. The second is a malignant case in a 70-year-old woman, showing intraductal carcinoma arising in intimate association with an EHT. These cases are presented in the context of a review of cases reported in the English literature. The exact origin has not been identified, but is considered to be of branchial apparatus, creating a quandary about the best terminology. Recently, the designation "branchial anlage mixed tumor" or "thymic anlage tumor" were proposed, but do not quite reflect the true nature of the neoplasm. To avoid taxonomic confusion, international consensus on terminology is desired. As this entity is a neoplasm that shows dual mesoderm and endoderm derivation/differentiation, we propose a new name "biphenotypic branchioma."