Cystic hygroma is a benign lymphatic malformation characterized as macrocystic, with collections of large lymphatic cysts lined by endothelium. It may occur anywhere on the body but typically involves the neck (75%) or axillae (20%). Less common sites (5%) are the mediastinum, retroperitoneum, abdominal viscera, groin, bones, and scrotum. There is no sex predilection.

The frequency is 1 in 6000 births. Most lesions (65%) are present at birth; otherwise, lesions present by the age of 2 years.

Lesions occur in otherwise healthy infants, but there is an association with Turner, Down, Edwards, and Noonan syndromes. Aside from an associated chromosomal abnormality, airway obstruction is the most critical complication.

Cystic hygromas arising in adults have rarely been reported in the literature, with some cases thought to be associated with traumatic exposure.

Complications include infections that most commonly occur secondary to trauma or following an upper respiratory infection. Infected cystic hygromas may present with pain, fever, and/or erythema. Infection can also result in rapid enlargement of the mass, which may cause airway compromise. An additional complication of cystic hygromas includes hemorrhage, which should be considered with an enlarging, painful lesion in a child with evidence of acute blood loss.