A healthy 6-month-old female with recent upper respiratory infection who has been found to have a cystic hygroma presents for magnetic resonance imaging to determine the extent of the lesion. She developed stridor after her respiratory infection.

Neck x-ray: Large soft tissue growth in left lateral neck with mild tracheal deviation, trachea patent.

Physical exam: 7 kg. Large, mobile, bluish soft tissue bulge in lateral neck. Inspiratory stridor 99% O₂ saturation on room air.

Cystic hygroma, also known as cystic lymphangioma, is a benign congenital malformation of the lymphatic system that typically affects the head and neck (75% of the time) with a left predilection, the axilla (20% of the time), and, more infrequently, the mediastinum, groin, and retroperitoneum. It is a result of a failure of the lymphatics to connect to the venous system, abnormal budding of the lymphatic tissue, and sequestered lymphatic rests that retain their embryonic growth potential, resulting in penetration of adjacent structures and fascial planes leading to retention of secretions as a result of a lack of venous drainage.

The incidence of cystic hygromas is 1:12,000 births. More than 50% of cystic hygromas are present at birth, with 80-90% presenting by age 2. Some people believe that all cystic hygromas are present at birth but are undetected. They can be visualized prenatally with ultrasound by 10 weeks’ gestation. They often present after a sudden increase in size as a result of an upper respiratory infection or intralesional bleeding. Spontaneous shrinkage or decompression of a cystic hygroma is uncommon. Giant cystic hygromas can involve both sides of the face and neck and extend to the mediastinum, causing acute airway obstruction and compression of the main vessels.

Genetic abnormalities are present in 25-75% of children with cystic hygroma. They are commonly found in Turner syndrome, Down syndrome, Klinefelter syndrome, trisomy 18, and trisomy 13. In addition, intrauterine alcohol exposure has been associated with cystic hygroma formation.

When cystic hygroma is suspected prenatally, patients should undergo chromosomal analysis or amniocentesis. Magnetic resonance imaging is the gold standard test to delineate the composition, location, and extent of the lesion. Careful observation of the cystic hygroma is recommended for asymptomatic patients only, and while medical treatment with sclerosing agents is available, the definitive treatment is still surgical excision in one- or multistage resections.