Mediastinal rhabdomyoma.

An 80-year-old black male with gastric adenocarcinoma, liver metastases, and parathyroid adenomas also had a rhabdomyoma of the anterior-superior mediastinum. This appears to be the first reported case of mediastinal rhabdomyoma in the literature. The ultrastructural demonstration of haphazardly arranged myofilaments with prominent Z bands and the absence of demosomes indicates that it is of extra-cardiac type. The probable origin of this tumor from the myoid cells of the thymus is discussed.