Mediastinal Thymolipoma: A Rare Occurrence with Striated Myoid Cells

We describe a 49-year-old man who presented to hospital with unstable angina and who underwent emergency coronary artery bypass grafting. During the surgical procedure, an incidental anterior mediastinal mass was discovered. Histological examination of this mediastinal mass revealed a thymolipoma containing numerous polygonal, striated myoid cells that were immunoreactive for desmin, muscle-specific actin and myoglobin. Electron microscopy demonstrated numerous Z band structures confirming myoid differentiation. Even though the appearance of myoid cells in thymolipoma may be alarming, this tumor should be recognized as a benign entity. Thymolipomas containing striated myoid cells should be differentiated from more ominous thymic neoplasms, including teratomas and thymic liposarcomas. To our knowledge, this is only the third reported case of thymolipoma containing striated myoid cells.