Thymolipoma with sebaceous differentiation: a hitherto unreported variant of thymolipoma

Thymolipoma is a very rare anterior mediastinal mass of thymic origin, accounting for only 2% to 10% of all thymic neoplasm. Histologically, the tumor is usually composed of adipose tissue interspersed with thymic tissues. We report a case of a 58-year-old man who presented with a few weeks history of shortness of breath, cough, and chest pain, found to have a retrocardiac infiltrate on chest X-ray. Computed tomography scan of the chest showed a large anterior mediastinal mass. Surgical excision revealed an ovoid fatty mass, which on histological examination displayed thymic tissue intermixed with lipomatous tissue consistent with a thymolipoma. Of note was the presence of a microscopic nodule of thymic epithelial proliferation with sebaceous differentiation and focal cylindroma-like architecture. Although sebaceous tissue has been rarely reported in thymic tissue, to the best of our knowledge, this is the first case report of sebaceous differentiation in a thymolipoma.