A cystic hygroma is a fluid-filled sac that forms on the head or neck of a baby due to blockages in the lymphatic system. The lymphatic system is a network of organs and tissues that helps move fluids and white blood cells through the body.

A cystic hygroma is a benign cyst, meaning it is not cancerous. It can occur during pregnancy, and is usually detected during the 11-14 week dating ultrasound scan that is offered to all women.

A cystic hygroma is considered abnormal and would result in referral to a fetal medicine specialist who would offer tests such as CVS or amniocentesis to investigate why it had occurred in the pregnancy. Some cases of cystic hygroma happen due to an underlying genetic or chromosomal condition such as Turner’s syndrome, or Noonan’s syndrome. In other cases a cause is not found in the baby. The cystic hygroma may spontaneously resolve during pregnancy, in which case the outlook is good.

More information on cystic hygroma and treatment can be found here.