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.
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