The Connection Between Turner Syndrome and Cystic Hygroma

The presence of a cystic hygroma on a prenatal ultrasound often prompts investigation into underlying genetic conditions, with Turner syndrome being a common finding. Understanding what these conditions are, how they are related, and the diagnostic process can provide clarity. This article explores the specifics of Turner syndrome and cystic hygromas, the biological connection between them, and what a diagnosis means for an individual’s health.

Understanding Turner Syndrome

Turner syndrome is a genetic condition that affects the development of individuals assigned female at birth. It results from a chromosomal abnormality where cells have only one fully functioning X chromosome instead of the usual two. This change occurs as a random event during the formation of reproductive cells in a parent and is not inherited.

The most common form is Monosomy X, where every cell in the body is missing an X chromosome, represented as 45,X. Another variation is mosaic Turner syndrome, where the chromosomal change does not occur in every cell. The features of Turner syndrome can vary widely among individuals, partly depending on whether the condition is monosomic or mosaic.

Common physical characteristics include short stature, a low hairline at the back of the neck, and low-set ears. Swelling of the hands and feet, known as lymphedema, may be present at birth. Internally, individuals may have developmental differences in the heart and kidneys, and the ovaries often do not develop properly, which can lead to incomplete puberty and infertility without hormone therapy.

What is a Cystic Hygroma?

A cystic hygroma is a malformation of the lymphatic system that appears as a fluid-filled sac, or cyst. These structures, also known as lymphangiomas, are benign and result from a blockage in the lymphatic vessels. The lymphatic system is a network that transports lymph fluid to help remove waste from the body. When these vessels fail to connect properly to the venous system, lymph can accumulate in soft tissues, creating a cyst.

These growths most commonly appear on a baby’s head or neck but can also form in the armpits or groin. On a prenatal ultrasound, a cystic hygroma is visible as a single or multi-chambered fluid-filled space at the back of the fetal neck. It is distinct from the nuchal translucency, which is a normal fluid-filled space measured during first-trimester screening; a cystic hygroma is a structural anomaly.

While frequently associated with genetic conditions like Turner syndrome, they can also occur as an isolated finding or with other chromosomal abnormalities. The presence of a cystic hygroma signals a disruption in the formation of lymphatic pathways, which occurs around the fifth week of gestation.

The Connection: Cystic Hygroma in Turner Syndrome

The frequent co-occurrence of cystic hygroma in fetuses with Turner syndrome stems directly from the syndrome’s genetic basis. The X chromosome contains genes that guide the development of the lymphatic system. In Turner syndrome, the absence of one X chromosome leads to haploinsufficiency, where the single remaining copy of these genes is insufficient to direct normal lymphatic vessel formation.

This genetic shortfall can cause the developing lymphatic sacs to fail to connect properly with the jugular vein in the neck. This connection is needed to drain fluid from the head and neck back into the circulatory system. This process explains why the neck is the most common location for these growths in fetuses with Turner syndrome.

The severity of the lymphatic abnormality can vary. The classic 45,X karyotype is often associated with more significant findings, such as large, septated cystic hygromas. These septations, or walls within the cyst, are visible on ultrasound and suggest a more complex malformation. The fluid buildup can also manifest as lymphedema in the hands and feet of newborns with the condition.

Diagnosis During Pregnancy

The detection of a cystic hygroma is often the first sign that leads to a prenatal diagnosis of Turner syndrome. During a routine ultrasound, a sonographer may identify a fluid-filled structure at the back of the fetal neck. The appearance of a cystic hygroma, particularly if it is large or has internal septations, prompts a recommendation for further testing to determine the cause.

After an ultrasound finding, genetic screening or testing is recommended. Non-invasive prenatal testing (NIPT) is a screening method that analyzes fetal DNA in the mother’s blood to assess the risk for certain chromosomal conditions. While NIPT can indicate a high probability of Turner syndrome, it is not a definitive diagnosis.

To confirm the diagnosis, an invasive procedure like chorionic villus sampling (CVS) or amniocentesis is required. These tests provide fetal cells for a karyotype analysis, which is a detailed examination of the fetal chromosomes. A karyotype can definitively identify the 45,X chromosomal arrangement or its mosaic variants. Genetic counseling is an important part of this process, helping parents understand the results and implications.

Health Outlook and Supportive Care

The health outlook for a fetus with both Turner syndrome and a cystic hygroma is variable. The presence of a large cystic hygroma is associated with a higher rate of fetal loss, especially if it leads to hydrops fetalis. This condition is a severe, generalized accumulation of fluid that significantly reduces the chance of survival.

In some instances, particularly if the hygroma is smaller and hydrops does not develop, the growth may resolve on its own before birth. If the hygroma resolves and the baby is born, the focus shifts to lifelong supportive care for the health issues associated with Turner syndrome. Infants will require monitoring by specialists, including cardiologists and nephrologists, to manage potential heart and kidney abnormalities.

Ongoing medical care for individuals with Turner syndrome involves a multidisciplinary team. This often includes hormone replacement therapy to induce puberty and support bone health, as well as regular check-ups for conditions like thyroid disorders and hearing loss. While the prenatal finding of a cystic hygroma signals risks, its resolution can lead to a positive long-term outcome with consistent medical support.