CTICasesThymic Hyperplasia Associated with Graves Disease
Imaging findings
CT and PET-CT in a young woman demonstrate a homogeneous, bilobed soft tissue mass in the prevascular mediastinum with mild diffuse FDG uptake and no internal fat lobulation, initially suspected to be lymphoma. The thyroid gland is diffusely enlarged with increased FDG uptake consistent with diffuse toxic goiter.
Key takeaways
Thymic hyperplasia is a recognized complication of autoimmune thyroid disease, particularly Graves disease and Hashimoto thyroiditis, due to shared immune dysregulation. The enlarged thymus can closely mimic lymphoma on CT and PET-CT. Key distinguishing features include the lower FDG avidity compared to lymphoma, a wraparound morphology, and the concurrent finding of autoimmune thyroid disease. Awareness of this association can prevent unnecessary biopsy.
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