Invasive thymoma with osseous metaplasia and cystic change in a case of myasthenia gravis: a rare presentation.

A 35-year-old woman, a known case of myasthenia gravis, was found to have an anterior mediastinal mass, which was surgically removed. The preoperative clinical and radiologic diagnosis was that of a thymoma, but foci of calcification and prominent cystic change suggested the remote possibility of a teratoma. Histopathologically, it was confirmed to be a type B3 invasive thymoma with intratumoral ossification. Up to the present, three cases of thymoma with osseous metaplasia, including only one with myasthenia gravis, have been reported in the English literature. The present case report highlights the rare occurrence of osseous metaplasia in thymomas and the diagnostic challenge that it can pose, especially if it is associated with cystic degeneration.