Cystic hygroma is a congenital lymphatic malformation—a fluid-filled sac that develops due to an error in the lymphatic system. While not solely genetic, its presence is frequently associated with underlying genetic factors and chromosomal abnormalities. Understanding this complex etiology, which involves both inherited and non-inherited components, is key to comprehending the diagnosis.
Understanding Cystic Hygroma Definition and Types
A cystic hygroma is a type of lymphangioma, an abnormal growth of the lymphatic system that typically develops during the first trimester of pregnancy. The lymphatic system is a network of vessels and organs that moves lymph fluid throughout the body. The hygroma forms when lymphatic vessels fail to connect properly, causing lymph fluid to collect in one or more sacs, most commonly in the neck or axillary (armpit) regions.
Although the neck area accounts for about 75% of all cases, cystic hygromas can also be found on the chest wall, abdomen, or groin. These malformations are classified based on the size of the fluid-filled cavities: Macrocystic hygromas contain large cysts, microcystic hygromas consist of many smaller cysts, and a mixed type includes both. This classification influences the choice of medical management and treatment approach.
Genetic Links Chromosomal Abnormalities and Syndromes
Cystic hygroma is strongly linked to specific chromosomal abnormalities. Approximately 50% of fetuses diagnosed with the condition have an abnormal number of chromosomes, making genetic testing a standard procedure following diagnosis.
The most frequent chromosomal abnormality associated with cystic hygroma is Monosomy X, resulting in Turner Syndrome (where a female has only one X chromosome). Other common associations include trisomies, which are the presence of an extra copy of a chromosome. These include Trisomy 21 (Down Syndrome), Trisomy 18 (Edwards Syndrome), and Trisomy 13 (Patau Syndrome).
Beyond whole chromosome errors, cystic hygroma can also be a feature of certain single-gene disorders. Noonan Syndrome, caused by a mutation in specific genes, is frequently associated with the condition. Other rare conditions like Multiple-pterygium syndrome and Fryns syndrome are also linked to this lymphatic malformation.
Sporadic Cases and Other Developmental Factors
While many cases are tied to genetic or chromosomal abnormalities, many instances are considered “sporadic,” meaning no identifiable genetic cause is found. In these cases, the hygroma is thought to be a localized, non-inherited error in lymphatic system formation during the first few weeks of fetal development. This failure of the lymphatic vessels to properly connect to the venous system causes the fluid to back up and form the cyst.
These non-genetic cases are often attributed to developmental “accidents” that occur early on. Although some studies suggest environmental factors, such as maternal viral infections or exposure to drugs or alcohol, might play a role, these are not typically the primary cause. When a cystic hygroma is isolated and resolves on its own during pregnancy, the fetus is much less likely to have an underlying chromosomal abnormality.
Diagnosis and Management Approaches
Cystic hygroma is most frequently diagnosed prenatally during a routine ultrasound, often appearing as increased nuchal translucency (excess fluid at the back of the fetal neck). If visualized, confirmatory prenatal diagnostic testing is offered to determine the underlying cause. These tests include chorionic villus sampling (CVS), performed earlier in pregnancy, or amniocentesis, usually done after 15 or 16 weeks of gestation.
These invasive procedures collect fetal cells for karyotyping or chromosomal microarray analysis. Management following diagnosis is individualized, depending on the size, location, and presence of associated conditions. Treatment options are generally reserved until after birth and include complete surgical excision for localized masses or sclerotherapy, which involves injecting a substance into the cyst to cause inflammation and shrinkage.
Genetic Counseling and Future Recurrence Risk
Genetic counseling plays a role for families following a cystic hygroma diagnosis, providing a personalized assessment of the condition and the likelihood of recurrence. A genetic counselor interprets prenatal testing results to determine the recurrence risk for future pregnancies. If the hygroma was associated with a de novo (new) chromosomal error, such as a sporadic case of Turner Syndrome, the risk of recurrence in a subsequent pregnancy is considered low.
If the underlying cause is an inherited genetic syndrome, particularly one with an autosomal recessive pattern, the risk of recurrence can be as high as 25% in each future pregnancy. Counseling also includes reviewing family and reproductive history, which can alert providers to the possibility of a recessive monogenic condition even when initial karyotyping is normal. The specific genetic test findings guide the counselor in providing accurate information for future family planning.