[Thymic cyst in the neck. Apropos of a case].

Cervical thymic cyst is an uncommon lesion. It is usually diagnosed after cervicotomy for lateral swelling of the neck. We present a case in a 12-year-old boy. Clinical diagnosis was cystic hygroma, but computed tomography revealed extension of the cyst to the anterior mediastinum, suggesting its thymic origin. Successful excision was performed through a neck incision alone. There has been no recurrence of the cyst nor immune deficiency within a 2-year follow-up. Pathogenesis and diagnostic modalities are discussed.