Ectopic thymic hyperplasia in a patient treated for Burkitt lymphoma.

Thymic hyperplasia results from thymic regrowth after atrophy during stressful conditions such as burns, surgery, infection, and chemotherapy. Although thymic lesions are relatively common causes of anterior mediastinal masses, they also can develop in other mediastinal compartments on rare occasions. It is well known that thymic tissue can develop in ectopic intrathoracic lesions. Few cases of ectopic thymus associated with disturbance during thymus embryogenesis have been reported as incidental findings. We report the case of a 4-year-old boy with true thymic hyperplasia from an ectopic thymus after successful treatment for Burkitt lymphoma. This is a rare finding in the differential diagnosis of a middle mediastinal mass in a child following chemotherapy for lymphoma. The diagnosis of thymic hyperplasia from an ectopic thymus can be confirmed only histologically.