Chemical-shift MRI of rebound thymic hyperplasia with unusual appearance and intense 18F-FDG uptake in adulthood: report of two cases

Rebound thymic hyperplasia (RTH) with increased 18F-FGD uptake at positron emission tomography (PET) computed tomography (CT) is typical of pediatric patients after chemotherapy, although it may occasionally occur in adults. At CT, RTH usually appears as a diffusely enlarged thymus with areas of fatty attenuation. We report two cases of RTH in adults detected at follow-up: both showed unusual morphology on CT and were confirmed at PET-CT as areas of strongly increased radiopharmaceutical uptake, which suggested disease recurrence. Chemical-shift magnetic resonance imaging, however, demonstrated fat infiltration within the tissue. Such finding was consistent with the diagnosis of RTH and was paramount in preventing unnecessary invasive procedures or treatments.