Ectopic thymus presenting as neck mass.

A 3-month-old girl presented with an asymptomatic soft tissue mass in the right neck. Her preoperative data were normal. CECT of the neck showed a 3-cm solid mass with homogeneous mild enhancement without mass effect. CECT of the thorax showed a normal thymus. MR images showed a right submandibular mass with signal intensity identical to that of the mediastinal thymus. Although it was difficult to make a correct preoperative diagnosis, surgical microscopic examination demonstrated normal thymic tissue. Because ectopic thymus can occasionally present with life-threatening symptoms, and malignant transformations have been documented, complete excision of cervical ectopic thymus was advocated.