A cystic hygroma is a fluid-filled sac that results from a blockage in the lymphatic system. It is most commonly located in the neck or head area, but can be located anywhere in the body. It may be discovered in a fetus during a pregnancy ultrasound, or it may be apparent at birth as a soft bulge under the skin. When it is identified on pregnancy ultrasound, there is an increased risk for miscarriage. In some cases, it is not discovered until a person is older. Symptoms can vary depending on its size and specific location, and it can potentially cause problems with nearby structures or organs.

A cystic hygroma may be caused by genetic or environmental factors that cause abnormal development of the lymphatic vascular system during embryonic growth. It may occur on its own or as part of a genetic syndrome with other features, such as Turner syndrome, Down syndrome or Noonan syndrome. In adults it may result from trauma, or from earlier respiratory infections. In many cases, the cause is not known.

Treatment involves removing the cystic hygroma, although removing all of it may not be possible. Other treatments that have been tried with limited success include chemotherapy, injection of sclerosing medicines, radiation therapy, and steroids.

The signs and symptoms of a cystic hygroma can vary depending on its size and location. Regardless of size, a cystic hygroma can potentially cause functional impairment of nearby structures or organs, as well as disfigurement of affected areas. When identified after birth, it most often looks like a soft bulge under the skin. The overlying skin may have a bluish tint. The cystic hygroma typically grows as the child grows, and may become apparent after a sudden increase in size, due to an infection or bleeding within the cyst. Feeding difficulties and failure to thrive may be present. Rarely, a child with a cystic hygroma may have symptoms of obstructive sleep apnea. Other symptoms or complications may include airway obstruction, hemorrhage, infection, or deformation of surrounding bony structures or teeth (if it is left untreated).

Treatment options for a cystic hygroma depend on the size, location and symptoms present. Options may include surgery (recommended when possible), percutaneous drainage, sclerotherapy, laser therapy, radiofrequency ablation, or medical therapy. These different treatment options may be used in various combinations. When surgery removes all abnormal tissue, the chance of complete recovery is good. If complete removal is not obtained, the cystic hygroma will often return. In very rare cases, a cystic hygroma will shrink or go away without treatment.

Cystic hygromas detected prenatally on ultrasound are associated with an increased risk for chromosome abnormalities (particularly Down syndrome) and birth defects (particularly heart defects). Both of these increase the risk for miscarriage, hydrops, fetal demise, and neonatal death. Increasing size is associated with an increasing risk of an underlying abnormality.

As a person with a cystic hygroma ages, morbidity is often related to cosmetic disfigurement and how the cystic hygroma affects other critical structures, such as nerves, blood vessels, lymphatics, and the airway. Quality of life can be significantly impaired in many cases. Recurrent inflammation can lead to cellulitis, which can cause pain and disfigurement of the affected area. Bleeding in the lesion can cause rapid pain, hardening, and swelling or enlargement of the affected area. Complications from surgery may also occur, and depending on the location may include damage to neurovascular structures (including cranial nerves), chylous fistula or chylothorax (leakage of lymphatic fluid), or hemorrhage. Specific possible complications, and areas of the head or body affected, will vary from person to person.

Some studies have reported an associated mortality rate of up to 2-6%, usually due to pneumonia, bronchiectasis, or airway compromise.

Unfortunately for the rare diseases, there is often not a calculated incidence or prevalence rate. There is no official method for tracking these conditions and no official statistics exist, only estimates. In our search of the medical literature, the most commonly quoted incidence estimate for cystic hygroma is 1 in 6,000 live births. This means that approximately 1 baby in 6,000 is born with a cystic hygroma.