A cystic hygroma is a fluid-filled sac that results from a blockage in the lymphatic system. The lymphatic system is a network of vessels that maintains fluids in the blood, as well as transports fats and immune system cells. Cystic hygromas are thought to arise from failure of the lymphatic system to communicate with the venous system in the neck. Cystic hygromas are single or multiple cysts found mostly in the neck region. A cystic hygroma in a developing baby can progress to hydrops (an excess amount of fluid in the body) and eventually fetal death.
Cystic hygromas occur in approximately 1% of fetuses between weeks 9 and 16 of pregnancy.
The majority of prenatally diagnosed cystic hygromas are associated with one of the following: Turner Syndrome (Monosomy X- an abnormality where a female has only one X chromosome, not two), Trisomy 13, Trisomy 18 (Edward's Syndrome), Trisomy 21 (Down Syndrome) and Noonan Syndrome. For a baby with no known genetic or chromosomal abnormality, a cystic hygroma may be caused by a birth defect (heart defect, digestive system defect, musculo-skeletal defect, etc.). In some situations, a cystic hygroma can be present in a healthy baby.
Overall, there is generally a poor prognosis associated with fetal cystic hygromas. In cases where genetic or chromosomal abnormalities were not present, there is research to indicate that a cystic hygroma may resolve on its own. In cases where a cystic hygroma did not resolve on its own by 20 weeks gestation, the outcome was generally poor. Hydrops (retaining of fluids in the body) results from vascular damage and high output heart failure. Hydrops occurs up to 75% of the time with a cystic hygroma and is almost always associated with miscarriage or fetal death.
Recurrence of fetal cystic hygroma in subsequent pregnancies is extremely rare. I have only found around 20 documented cases that have been published in medical research. While it is possible that it can happen by chance and be caused by completely unrelated events, it is unlikely. There is literature to suggest that recurrence can be the result of a familial inheritance pattern, most likely an autosomal recessive gene.