[A Case of Infantile Cervical Ectopic Thymus].

We report herein on a case of ectopic cervical thymus in a 5-year-old boy and the literature is reviewed. Swelling of the right neck was seen in the patient in his newborn period and it was diagnosed as cystic disease of the neck in a previous hospital at 4 months of age. Ultrasonography (US) and MRI revealed a cervical tumor consisting of a solid component in our hospital, and histopathologic examination showed no evidence of malignancy. The lesion revealed almost no change in size but showed a mosaic pattern on US, whereon the parents agreed to the removal of the tumor. Intraoperatively, the tumor could be easily dissected from the surrounding tissue and resected. The pathological diagnosis was normal thymic tissue. The postoperative course was uneventful and no complication or immunological disorders were seen. A cervical ectopic thymus is a congenital lesion that results from abnormal thymic migration during embryogenesis. Most patients are asymptomatic and the condition is found incidentally. Preoperative diagnosis of cervical ectopic thymus in children is rarely made, so surgical treatment is the definitive means of pathological diagnosis. This disease should be listed in the differential diagnosis for neck masses in children, and should be suspected when the mosaic pattern is detected in the lesion on US.