Challenges in diagnosing ectopic thymus tissue in children.

The presentation of a fast-growing cervical mass necessitates prompt attention due to risk of the mass effect on vital structures and requires preferential screening for infections, bleeding and malignancies in an extensive list of differential diagnoses. This case report describes a 4.5-year-old boy with a fast-growing, unilateral lesion in the neck, with clinical features in keeping with malignant characteristics. Surgical excision with pathocytological examination revealed an exceptional diagnosis of haemorrhage in an ectopic cervical thymic cyst. Thymic cysts are a rare cause of unilateral masses in the neck, usually presenting as an asymptomatic, painless, slow-growing or stable mass anywhere along the thymopharyngeal duct. Spontaneous haemorrhages in thymic tissue can occur, often due to coagulation defects. Treatment of symptomatic thymic cysts is based on surgical excision. Partial resection of the thymus should be encouraged if possible, since clinical consequences of removing all thymic tissue in children are still unclear.