Hemifacial microsomia is a condition in which one side of the face is smaller or underdeveloped or has parts that are missing. While the hallmark is unevenness (asymmetry) of the face, one or both sides may be affected. It is the second most common facial birth defect after cleft lip and palate. It happens more often in males than in females.

The condition usually affects the lower part of the face and may include the cheekbone, lower jaw, facial nerves, muscles, and ear. However, sometimes it affects the eye and forehead. Some babies born with hemifacial microsomia have minor facial changes, while others may have more severe changes to the face. The condition may also cause dental and speech problems along with difficulties feeding or eating, breathing, seeing, and hearing.

For most people with hemifacial microsomia, the cause is unknown. It is believed that something occurs in the early stages of development, such as a disturbance of the blood supply to the first and second branchial arches in the first 6 to 8 weeks of pregnancy.

Studies have suggested multiple possible risk factors for hemifacial microsomia. Environmental risk factors include the use of medications during pregnancy such as Accutane, pseudoephedrine, aspirin, or ibuprofen. Other environmental factors include second trimester bleeding, maternal diabetes, being pregnant with multiples, or the use of assisted reproductive technology. A genetic cause is found in some families, such as a chromosome disorder or a genetic syndrome.

Some possible explanations when the cause of hemifacial microsomia is unknown include a very small chromosome deletion or duplication that is not detected, a mutation in an unknown gene, or changes in multiple genes associated with development of the face. It is also possible that a combination of genetic changes and environmental risk factors could cause hemifacial microsomia.

Hemifacial microsomia most often occurs in a single individual in a family and is not inherited. If the condition is caused by a chromosomal abnormality, it may be inherited from one affected parent or it may result from a new abnormality in the chromosome and occur in people with no history of the disorder in their family. In a very small number of cases, hemifacial microsomia is inherited in an autosomal dominant pattern, which means one copy of an altered gene in each cell is sufficient to cause the disorder. In rare cases, the condition is inherited in an autosomal recessive pattern, which means both copies of a gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. The gene or genes involved in hemifacial microsomia are unknown.

In some affected families, people seem to inherit an increased risk of developing hemifacial microsomia, not the condition itself. In these cases, some combination of genetic changes and environmental factors may be involved.

The signs and symptoms of hemifacial microsomia vary; however, most of the time, the ear and lower jaw are affected. See the chart below for possible signs and symptoms of hemifacial microsomia and the areas that can be affected by the condition.

Babies and children with hemifacial microsomia also may have medical problems involving the spine, ribs, heart, and kidneys that should be evaluated.

Changes in the face can sometimes be seen in an ultrasound during pregnancy, and the physician may suspect hemifacial microsomia before birth. However, doctors usually diagnose hemifacial microsomia by examining the face after the baby is born. The doctor also may order x-rays and a CT scan to evaluate the bones, muscles, and tissue structures of your baby’s face.

The doctor may order genetic testing if there are others in the family with features of hemifacial microsomia, or if he or she wants to rule out other conditions that may be associated with some of the same symptoms.

After diagnosis and testing, your child’s doctor may refer you to a craniofacial center for evaluation and treatment planning. These centers, which are usually part of children’s hospitals or university medical centers, have a team of health care professionals who will provide a complete treatment plan.

Treatment depends on your child’s symptoms and overall general health. When your child is an infant, treatment focuses on making sure your baby is breathing and feeding well. When your child is older, the goal is to improve the evenness of the face, jaw movement, and bite. You will work with your child’s doctors to develop a specific treatment plan, which may include surgeries to repair, rebuild, and expand the upper and lower jaws, improve the evenness of the face, or reconstruct or repair the ear.

In addition to surgeries, your child may need other treatments, such as a feeding tube to provide nutrition, speech therapy, dental care and orthodontia, or hearing and vision aids.

Treatment may occur over many years to adjust the shape of your child’s face and to help him/her breathe, eat, speak, and hear. Overall, the goal remains the same: to help your child develop and thrive.

• Before visiting a doctor, write down questions or topics you would like to discuss at the appointment.
• Ask your health care team questions and write down their answers. If you don’t understand something, ask them to explain.
• After each visit, write down any tests, treatments, or instructions you received. This can help you remember them and communicate with other members of your child’s health care team.
• Remember to take your child to the dentist for regular checkups. Discuss with the dentist the dental care and teeth cleaning routine your child should follow at home.
• Ask your physicians for community resources or support groups in your area for both you and your child.
• Ask for support from family and friends.