Giant Cystic Hygroma of the Thymus in a Child

Abstract

A 4-year-old asymptomatic boy was found to have a large multicystic mass occupying the anterior mediastinum and approximately 80% of the left chest cavity. The lesion was resected and consisted of a large cystic hygroma measuring 18.0 cm in largest dimension, involving the thymus and the adjacent mediastinal soft tissues. The multicystic spaces were filled with straw-colored fluid, consistent with old hemorrhage, and were lined by endothelial-lined vascular spaces showing smooth muscle bundles and patchy lymphoid aggregates in their walls. Focal areas of stromal calcification were present. No teratomatous elements were identified within the mass. The patient recovered fully from the surgical procedure. Cystic hygromas (cystic lymphangiomas) are unusual tumors in children that usually develop in the neck but have been described in the thorax, abdomen, extremities, and other locations. Approximately 10% of cervical cystic hygromas extend to the mediastinum, but primary mediastinal lymphangiomas are extremely rare neoplasms that have been described mostly in fetuses and a few children and adult patients. The clinicopathologic findings of this unusual case and the differential diagnosis of mediastinal cysts in young children are discussed.