Cystic hygromas are anomalies of the lymphoid system characterized by single or multiple cysts within the soft tissues, that occur at sites of lymphatic-venous connection, usually in the posterior neck but also axillary or cervico-mediastinal.. They are frequently found in associationĀ with chromosomal aberrations (mainly Turner"s syndrome), various malformation syndromes, and several teratogenic agents. Large cystic hygromas like this one (1.5 MB video) are fatal. Also note the abnormal heart, although no autopsy was performed.