An ectopic hamartomatous thymoma.

An ectopic hamartomatous thymoma is an extremely rare benign tumor of the lower neck that is the most common in middle-aged males. Pathologically, the tumor is characterized by a mixture of spindle cells, epithelial cells, mature adipose tissue, and lymphocytes. The histogenesis of this tumor is controversial. Recently, an origin from a remnant of the cervical sinus of His was proposed. Malignant lesions such as synovial sarcomas or malignant peripheral nerve sheath tumors can have similar clinical features and radiologic images. Thus, recognition of this tumor is important because it follows a benign clinical course and conservative surgical excision is the treatment of choice. Here, we report the case of a 34-year-old man with an ectopic hamartomatous thymoma in the left supraclavicular region and a review of the literature on this tumor.