[Ectopic hamartomatous thymoma. Case report with special reference to differential diagnosis].

We report the case of an ectopic hamartomatous thymoma in a 56-year-old male patient. The lesion arose subcutaneously in the supraclavicular region. Histologically, the well-circumscribed but unencapsulated tumour was composed of uniform fusiform tumour cells. In addition, mature fatty tissue, scattered T-lymphocytes, and an epithelial and a myoepithelial tumour cell component were found. The epithelial differentiation of the spindle cell tumour component was confirmed immunohistochemically and by electron microscopy. Ectopic hamartomatous thymoma has to be distinguished from ectopic cervical thymoma, thymolipoma, ectopic salivary tissue, teratoma, peripheral nerve sheath tumours, malignant epithelial tumours with thymus-like differentiation, biphasic synovial sarcoma, and skin adnexal tumours.