Cystic hygroma. Coloured magnetic resonance imaging (MRI) scan of a coronal (frontal) view through the neck of a 2-year-old male patient with a cystic hygroma (yellow). A cystic hygroma is a congenital condition manifesting itself as a slow- growing fluid-filled growth of the lymphatic tissues. It may be single or multiple. Cystic hygromas may spontaneously reduce or disappear. Treatment involves the removal of the abnormal tissue. However, cystic hygromas often invade other neck structures and in these cases the use of steroids, radiation therapy and chemotherapy agents have been used with limited success.