Thymic rebound hyperplasia is considered a from of true thymic hyperplasia.
In periods of bodily stress the thymus may acutely shrink to 40% of its original volume (depending on the severity and duration of the stress). During the recovery phase it can grow back to its original size or even larger (up to 50% larger). This "rebound effect" is known as thymic rebound hyperplasia. It typically takes the thymus 9 months to return to its original size 1.
Examples of acute stress events that can trigger thymic atrophy and later rebound include:
- corticosteroid therapy
- radiation therapy
- post-chemotherapy 10-25% will undergo rebound hyperplasia, usually occurring within 2 years of treatment 2
Rebound hyperplasia is typically seen in children, but can also occur in adults 2.
Thymic rebound hyperplasia typically shows diffuse enlargement, a fine mixture of fat and lymphoid tissue, a smooth contour, and normal vessels 2.
The normal thymus is typically barely visible on PET. However, in rebound hyperplasia it show intense FDG uptake. This can lead to confusion, and misdiagnosis of lymphoma 3.
- 1. Webb WR, Higgins CB. Thoracic Imaging. Lippincott Williams & Wilkins. (2010) ISBN:1605479764. Read it at Google Books - Find it at Amazon
- 2. Kissin CM, Husband JE, Nicholas D et-al. Benign thymic enlargement in adults after chemotherapy: CT demonstration. Radiology. 1987;163 (1): 67-70. doi:10.1148/radiology.163.1.3823458 - Pubmed citation
- 3. Nasseri F, Eftekhari F. Clinical and radiologic review of the normal and abnormal thymus: pearls and pitfalls. Radiographics. 2010;30 (2): 413-28. Radiographics (full text) - doi:10.1148/rg.302095131 - Pubmed citation
- 4. Gawande RS, Khurana A, Messing S et-al. Differentiation of normal thymus from anterior mediastinal lymphoma and lymphoma recurrence at pediatric PET/CT. Radiology. 2012;262 (2): 613-22. doi:10.1148/radiol.11110715 - Pubmed citation
- 5. Bogot NR, Quint LE. Imaging of thymic disorders. Cancer Imaging. 2005;5 (1): 139-49. doi:10.1102/1470-7330.2005.0107 - Free text at pubmed - Pubmed citation