Fact: The incidence of hemihyperplasia is estimated to be 1 in 86,000.

What is hemihyperplasia?
Hemihyperplasia, also called hemihypertrophy, refers to overgrowth of one side of the body in comparison with the other. The overgrowth may be limited to a portion of the body, such as the legs, or it may involve several different areas of the body, including the arms, face (causing asymmetry of the nose, eyes or cheeks), tongue, jaw, teeth and ears. All tissue types can be affected, including the bones, skin, muscle, fat and nerves that are connected to the area of overgrowth.

Hemihyperplasia can occur by itself (isolated), or it can be one of several characteristics of Beckwith-Wiedemann syndrome or another genetic syndrome. It can be diagnosed at birth or appear later in childhood, and can follow an irregular growth pattern. At times new growth may be excessive, while at other times it may be modest.

No one is exactly sure what causes hemihyperplasia, but there is some evidence that the disorder runs in families. Genetics seem to play a role, but the genes that seem to cause hemihyperplasia can differ from person to person. A mutation on chromosome 11 is suspected to be associated with hemihyperplasia.

Statistics vary on how many people actually have this disorder. There are several reasons for this. First, the symptoms of hemihyperplasia are similar to other diseases, so sometimes the diagnosis can be confused with others. Also, sometimes the asymmetry or overgrowth of one side can be so slight that it isn’t easily recognizable.

What are the symptoms?
The most obvious symptom of hemihyperplasia is the tendency for one side of the body to be larger than the other side. An arm or a leg can be longer or larger in circumference. In some cases, the trunk or the face on one side is larger. Sometimes this isn’t really noticeable unless the individual lies on a bed or flat surface (called the bed test). In other cases, the difference in posture and gait (how someone walks) is noticeable.

Children with hemihyperplasia are at an increased risk for tumors, specifically those that occur in the abdomen. Tumors are abnormal growths that can be benign (noncancerous) or malignant (cancer). In hemihyperplasia, the cells that form a tumor have often lost the ability to stop or “turn off” the growth mechanism. Wilms’ tumor, which is a cancer that occurs in the kidneys, is the most common. Other types of cancerous tumors that are associated with hemihyperplasia are hepatoblastomas (of the liver), adrenocortical carcinomas (of the adrenal gland), and leiomyosarcomas (of the muscle).

How is it diagnosed?
A diagnosis is usually made by a physical exam. Symptoms are associated with other conditions, like Beckwith-Wiedemann syndrome (BWS), Proteus syndrome, Russell-Silver syndrome, and Sotos syndrome. Before diagnosing, your health care provider should rule these out. They may also order diagnostic imaging to screen for tumors.

Because this disorder is rare and often overlooked, it is recommended that the diagnosis be made by a clinical geneticist who is familiar with it.

What to do after diagnosis?
If you think your child has hemihyperplasia or if you have been diagnosed, consider the following:

  • Get a referral to a clinical geneticist for evaluation.
  • Know your doctor’s plan for tumor surveillance. Some guidelines recommend screening for tumors for the first six years. Others recommend abdominal ultrasounds every three months until the age of 7.
  • Consult your doctor on whether a serum alpha-fetoprotein (SAF) measurement should be taken. Some guidelines recommend that the SAF level be measured every three months until the age of 4. In some cases, the SAF, a type of protein, is very high in infants with hemihyperplasia.

If your child is diagnosed with hemihyperplasia, it is a good idea to regularly perform an abdominal examination of your child. Ask your doctor for recommendations on how to do this. Parental involvement in treatment has shown to be effective in some cases.


Treatment of hemihyperplasia addresses both functional and appearance-related purposes. Procedures performed include suction-assisted lipectomy, excision of excessive skin and subcutaneous tissue, and contouring or reducing facial bones.

The goal of surgery is to preserve as much nerve and muscle function as possible. Surgery can occur on an outpatient basis, or if it is more extensive it will require hospitalization for a one to two day period.

Incisions can vary around the face depending on the area that is hyperplastic but, in general, are hidden in creases, folds, or intraorally. A moderate amount of soft tissue swelling can occur following surgery and eating may be compromised short term following discharge. Swelling will improve over time and any numbness or the like as a consequence of the surgery will generally improve.

Information on this page taken directly from:​
Children's Hospital of Philadelphia

Want to learn more?

The following are organizations and/or websites dedicated to providing information and education surrounding Hemihyperplasia. These organizations are dedicated to research, education, awareness, and/or support. They are listed in Alphabetical order without any preference or prejudice. Listing these organizations is not a recommendation or referral in any regard for seeking treatment or consultation or support for treatment.

Children's Hospital of Philadelphia