Focal thymic hyperplasia in an adult: report of a case.

We report herein an unusual case of a 35-year-old Japanese man who underwent thoracotomy for a mass in the mediastinum which was found to be a well circumscribed localized tumor within the thymus. Focal thymic hyperplasia in adults is extremely rare and the clinicopathological features of this case were particularly interesting and posed great difficulty in establishing a diagnosis.