ABSTRACT
Lymphangiomas are congenital malformations of lymphatic vessels that have the potential to infiltrate surrounding structures. In 95% of cases, they are located in the neck (cystic hygroma), head and axilla. But they can occur in a variety of anatomical locations, such as the abdominal cavity, extremities and urinary bladder. Pathologically they can be classified into three group: lymphangioma simplex; carvenous lymphangioma; and cystic lymphangiomas or hygromas. Mixed lesions may coexist in different areas of the same lymphangioma. Although these lesions are benign, they have a propensity for rapid growth and invasion into the underlying muscles and connective tissues. A extensive mass can compress adjacent vital organs, which determines the severity of the lesion. Accurate prenatal diagnosis and anatomical evaluation are important as they permit planned delivery and prompt postnatal resuscitation, and allow the option of terminating the pregnancy if a poor outcome is predicted. Prenatal MRI can confirm ultrasonographic findings, provide detailed fetal anatomical evaluation, and demonstrate the extent and character of lymphangiomas. We present a case of a huge retroperitoneal cystic lymphangioma diagnosed prenatally using ultrasound and MRI at 26 weeks gestation.