Biphenotypic Branchioma of the Anterior Neck: A Case Report

We report a case of biphenotypic branchioma, formerly termed ectopic hamartomatous thymoma (EHT), occurring in the suprasternal region of a 54-year-old Asian man. The patient presented with a three-year history of a slowly enlarging, painless nodule. Microscopically, the tumour comprised spindle cells, epithelial nests, and mature adipose tissue. The spindle cells were arranged in fascicular and storiform patterns, epithelial areas formed squamous islands, and adipocytes were distributed in irregular clusters and sheets. Immunohistochemistry showed AE1/AE3 and CK7 positivity in both spindle and epithelial cells, and the spindle cells also expressed vimentin. All components were negative for CK20 and S100. The Ki-67 proliferation index was less than 10%.