Type AB thymoma with brain metastasis: Report of a case.

Type AB thymomas are considered to be nonaggressive tumors, and the great majority are classified as Masaoka stage I or II. This report presents a case with Masaoka stage I and type AB thymoma, which metastasized to the brain 2 years 5 months after removal of the primary tumor. The original mediastinal lesion was adhesive but not invasive to the lung. The patient is now alive with multiple tiny pulmonary metastases 3 years after complete resection of the brain metastasis. Some reports of recurrent thymomas have suggested that the presence of peritumoral adherence to the adjacent structures might be a risk factor for recurrence in patients with such noninvasive thymomas. During the development of fibrosis which thus causes adhesion, the tumor may have an increased chance to metastasize because of the increased vessels and lymphatics.