Hyperplasia of the thymic gland can occur in pediatric patients as a reactive process.
Thymic hyperplasia may go unrecognized if the patient is asymptomatic and no imaging studies are performed.
Features:
(1) diffuse enlargement of the thymus
(2) biopsy show reactive hyperplasia with a normal proportion of connective tissue
(3) other causes of thymic enlargement such as Hodgkin's disease or thymoma are excluded
(4) flow cytometry shows no clonal proliferation of lymphocytes
(5) the thymic enlargement reverses with time
If imaging studies are performed it appears as a mass in the anterior mediastinum.
Massive hyperplasia (weight > 100 g according to Arliss et al) may compress the trachea and cause dyspnea.
The thymus may shrink in size with steroid therapy. If the patient has respiratory distress then surgical resection may be performed.
A cause may not be found. Some cases are related to an autoimmune disease, especially Grave's disease. Viral infection and drug exposures need to be looked for.
