August 11, 2016
A 14-year-old boy with history of hepatocellular carcinoma on PET/CT (A, top) treated surgically, followed by 4 cycles of adjuvant chemotherapy, who presents for surveillance imaging (A, bottom; B–C).
Ectopic Thymus Mimicking Lymph Node Metastasis
- Background:
- The thymus gland is very sensitive to stresses such as chemotherapy.
- Following chemotherapy, it can rebound to a larger size, known as reactive thymic hyperplasia, which may be misdiagnosed as disease relapse.
- Homogeneous enlargement of the thymus in the presence of mediastinal or hilar lymphadenopathy may suggest lymphoma.
- Biopsy should be performed to obtain histopathologic confirmation and to avoid unnecessary chemotherapy.
- Clinical Presentation:
- Asymptomatic patient with history of prior hepatocellular cancer undergoing surveillance imaging
- Key Diagnostic Features:
- FDG-PET is well known as the modality used to stage cancers. However, tumors may be indistinguishable from reactive thymic tissue, as FDG uptake is increased in both.
- Tissue sampling is necessary to confirm the diagnosis of ectopic thymus.
- Differential Diagnoses:
- Reactive lymphadenopathy, lymphoma, metastatic disease, granulomatous disease
- Thyroid or parathyroid mass
- These lesions may be indistinguishable on both PET and cross-sectional imaging
- Treatment:
- None
