Report of a case of gross thymic hyperplasia in a child.

A large thoracic mass and a mediastinal lymph node were excised from an infant with a peripheral blood and bone marrow lymphocytosis. The 224-mass was composed of histologically normal thymus, and the lymph node architecture was partially effaced. Hypogammaglobulinemia was detected two years after thymectomy. The enormous thumus in this case fits the classic gross pathologic definition of hyperplasia. The possibility of associated thymic hyperfunction in this case is discussed.