A Rare Presternal Soft Tissue Tumor: Ectopic Hamartomatous Thymoma (Branchial Anlage Mixed Tumor)

Ectopic hamartomatous thymoma is a rare benign tumor in adults, mostly located in the lower neck region. It was first reported in 1982 by Smith and McClure. Histopathologically these tumors are typically well marginated and composed of a mixture of spindle cells, mature adipose tissue, and epithelial cells, including both glandular and squamous elements. The histogenesis of this tumor is controversial. Recently, an origin from a remnant of the cervical sinus of His was proposed. Ectopic hamartomatous thymoma needs to be differentiated from malignant lesions such as synovial sarcomas or malignant peripheral nerve sheath tumors. These tumors can have similar clinical features and radiologic images. Recognition of this tumor is important because it follows a benign clinical course and conservative surgical excision is the treatment of choice. To our knowledge, 61 cases have previously been reported. We present the case of a 45-year-old women with an uncomplicated presternal located ectopic hamartomatous thymoma. The morphological and immunohistochemical findings are discussed and a review of literature is made.