Cervical extension of the thymus mimicking metastatic recurrence of Ewing sarcoma on PET/CT

Occasionally the thymus may extend in the neck, from its normal location in the anterior mediastinum. The cervical extension, especially when the native thymus is hyperplastic, can mimic a mass. We describe the detection of cervical extension of the hyperplastic thymus, presenting as a suspicious recurrent soft tissue mass in the neck in a patient with Ewing's sarcoma.