Upper thymic prolongation simulating mediastinal lymphadenomegaly Prolongamento tímico superior simulando linfonodomegalia mediastinal

aBstract The thymus is located in the anterior portion of the upper mediastinum, immediately behind the sternal manubrium, and extends to the anterior mediastinum, anteriorly to the pericardium. Two patients were evaluated due to nodulations at the transition from the cervical region to the anterior mediastinum, which simulated lymphadenomegaly. The first patient, a seven-year-old male, presented with a rhabdomyosarcoma of the masticatory space; during progressive follow-up, a nodule was noted with FDG uptake on the positron emission tomography coupled with the computed tomography (PET-CT). The second patient, a 51-year-old female, presented with a nodulation characterized on the magnetic resonance image for follow-up of a papilliferous carcinoma of the thyroid. In both cases, the nodulation displayed an upper prolongation of the thymus. These nodulations showed the same density on the computed tomography and the same signal intensity on the magnetic resonance image as the adjacent thymic tissue, and there was no adipose tissue layer between the nodulations and the thymus. Knowledge of the upper prolongation of the thymus as an anatomical variation is vital for differentiating it from mediastinal lymphadenomegaly, thus avoiding unnecessary biopsies or procedures.