Ectopic thymus in the differential diagnosis of neck masses

Ectopic thymus is a rare benign cause of paediatric neck masses. Because of embryologic migrational defects, ectopic thymic remnants can be found along the descent pathway from the mandible angle to the superior mediastinum. Clinically, between 2 and 13 years of age, ectopic thymus presents as a painless neck mass, secondary to hyperplasia (like in the normal thymus gland). Ectopic thymus rarely determinates symptoms of compression of adjacent cervical structures. Radiologic imaging and biopsy (especially in cases of intra-thyroidal nodules) help to determine the nature of the mass. If ectopic thymus is definitively diagnosed before surgery, it can be treated conservatively. In asymptomatic cases surgery is not mandatory because there is no convincing evidence of malignant degeneration and bleeding is very rare and typical of adulthood. A spontaneous involution of thymic tissue after puberty is expected.