CTICasesThymic Hyperplasia Associated with Graves' Disease
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Imaging findings
Serial CT angiograms obtained six months apart show a dramatic interval increase in the volume of soft tissue in the anterior mediastinum. The tissue drapes over the mediastinal vessels, retains a typical triangular shape, and shows preserved fat interdigitated in the interstices without mass effect, characteristic of thymic hyperplasia. Lab work and thyroid scintigraphy confirm Graves' disease with elevated thyroid hormones, low TSH, and 73% diffuse thyroid uptake.
Key takeaways
Lymphoid thymic hyperplasia is a well-recognized but frequently misdiagnosed association with Graves' disease and other hyperthyroid states. On CT, the hyperplastic thymus can mimic a mediastinal mass, but it typically maintains its standard shape, drapes over the cardiovascular structures, and contains interspersed fat. Recognizing this benign association can prevent unnecessary biopsies or thymectomies, as the hyperplasia typically regresses once a euthyroid state is restored.
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