Thymic atrophy and regrowth in response to chemotherapy: CT evaluation.

Twenty-nine consecutive patients 2-35 years old underwent serial thoracic CT evaluations for metastatic disease. Thymic volumes were determined for each patient during cycles of chemotherapy and were compared with the patient's clinical status. This group included patients with Hodgkin's disease (13 patients), osteogenic sarcoma (five), testicular neoplasm (four), Wilms' tumor (three), rhabdomyosarcoma (two), malignant fibrous histiocytoma (one), and Ewing's sarcoma (one). Seven patients with mediastinal lymphoma had tumor involvement of the thymus and therefore were excluded. The 22 remaining patients showed cyclic thymic volume changes in response to chemotherapy or its discontinuance. During the first course of chemotherapy the thymic volume decreased by an average of 43% in 20 of 22 patients. Between the first and second course, regrowth was observed in all 20 of these patients. Among the six patients who received a second course of therapy, an average volume decrease of 36% was observed during the second course with regrowth again occurring during recovery from chemotherapy. Thymic rebound (regrowth 50% greater than baseline volume) occurred in five patients, three of whom were in clinical remission. The thymus appears to atrophy during the administration of chemotherapy and regrow during the recovery phase of chemotherapy in 90% of the patients studied. Thymic hyperplasia or rebound is a relatively common phenomenon occurring in 25% of patients. The size of the thymus appears to be extremely sensitive to chemotherapy.