What Is Hemifacial Microsomia?

Hemifacial microsomia is a birth defect that affects the development and appearance of the face. Hemifacial microsomia is the second most common birth defect, after cleft lip. Microsomia causes the structures of the face such as the jaw, cheek, lips, and skull to appear malformed.

Hemifacial microsomia affects only one side of the face. There are several potential causes behind the development of this condition, but all are linked to changes that occur during pregnancy. In many cases, the condition is spontaneous or the result of genetic errors that may occur during fetal development.

Fortunately, there are many treatments to correct the effects of hemifacial microsomia. These include surgical and dental procedures. This article will review the common causes, classifications, and treatments for hemifacial microsomia. 

Causes

The exact causes behind hemifacial microsomia are not well understood but are thought to be the result of errors in fetal development. Some theories suggest the condition is the result of abnormal blood flow and bleeding that occurs within the early fetus. Other theories have suggested that the cells responsible for forming the face, head, and spine fail to properly develop.

During pregnancy, the fetus develops from an egg, and the features that will become the face, cheeks, jaw, and mouth are formed. Facial development involves specific regions of the fetus called the branchial arches, which are located around the regions that will become the head, neck, and face.

As the fetus matures, the branchial arches combine to form the mouth, face, cheek, and jaw. When the fusion of the branchial arches is disrupted, there can be misalignment and malformation of the facial structures.

As a result, hemifacial microsomia can arise from this abnormal development during pregnancy. In some cases, the condition is very minor and only noticeable in certain areas such as the jaw. In other cases, the microsomia can alter the symmetry of the face, which then appears out of proportion. In extreme cases, facial features and structures can be significantly affected and critical functions like breathing or eating may be impacted.

Genetic Conditions

The causes of hemifacial microsomia are not completely understood and no exact cause has been identified. In fact, a majority of cases arise spontaneously during development, without a clear trigger. There are genetic conditions that carry a higher risk of hemifacial microsomia. This includes Goldenhar syndrome (also called Goldenhar-Gorlin syndrome, oculoauriculovertebral syndrome, and facioauriculovertebral dysplasia).

Some genetic abnormalities that have been linked to hemifacial microsomia are:

• Trisomy 10p
• 12p13.33 microdeletion
•  22q11.2 microdeletion
• Large 5p deletion
• 10.7 cM on chromosome 14q32

Symptoms and Classification

The signs of hemifacial microsomia may be apparent at birth. Possible symptoms include an underdeveloped eye, jaw, mouth, ear, or impaired opening of the mouth. In some cases, the structures may be deformed. The functional movements of the face may also be disrupted due to abnormal development of the nerves in the face.

A useful classification system known as OMENS has been developed to appropriately identify the impacted areas. The OMENS classification system is used by healthcare providers to better understand the areas and structures of the face that are affected by hemifacial microsomes since every child's situation is unique. Once the deformities and deficits are categorized, providers can work to develop a personalized plan of care and optimize treatment approaches.

Hemifacial microsomia may affect the following areas of the face:

• Eye socket (orbit): Abnormally small, closed, or altered vision
• Jaw (mandible): Crooked jaw, misaligned teeth, mandible motion, cleft lip or palate
• Ear: Absent or abnormal ear, misshapen ear, ear canal, impaired hearing 
• Nerves: Impaired function, any weakness, any abnormal feeling
• Soft tissues (including the skin, muscle, fat, tendons, and ligaments): Flattened cheeks or forehead, unequal cheek fullness, asymmetrical mouth with lateral cleft
  

Treatment

Hemifacial microsomia can affect multiple structures in the face, and many treatments focus on correcting the deformities through surgery. Surgery often focuses on reconstructing the face to correct facial symmetry and restore a natural appearance. Hemifacial microsomia can impact several different regions of the body at the same time. As a result, multiple doctors, surgeons, and other healthcare professionals may be involved in the care and treatment. 

Orthodontic Treatments 

The teeth and jaw are the most commonly affected structures in hemifacial microsomia. In some cases, the teeth can become overcrowded within the mouth, and some may be removed. Additionally, the jaw can develop out of proportion with the rest of the face, making it appear oversized.

Treatments for tooth and jaw deformities associated with microsomia are available. These include a procedure known as distraction osteogenesis, in which the jaw is lengthened by implanting a device in the jaw.

Another treatment is a bone graft procedure, in which a piece of bone is harvested from another part of the body and then used to expand the jaw and realign it to be proportional to both sides of the face. These procedures are often performed by surgeons with experience in repairing the mouth and face. 

Plastic and Facial Reconstruction

Surgery may be needed to ensure that the person can eat and breathe normally. In some severe cases, hemifacial microsomia can impact the ability to breathe and eat, which will require urgent correction. Once these key abilities have been restored, the focus can shift to correcting the appearance of deformities.

Plastic and reconstructive surgeons can help to restore the appearance and natural symmetry of the affected parts of the face. Procedures to correct hemifacial microsomia may include tissue transfers, muscle and skin grafts, fillers, and nerve repair. Often, as children grow, their facial structures change. Some treatments may be reserved for when children are older so that correction can be more successful. 

Ears and Hearing

The shape and appearance of the ear can sometimes be affected by hemifacial microsomia. In some cases, the ear canal and specialized structures within the ear responsible for hearing may also be impacted by hemifacial microsomia.

Audiologists, medical professionals who test hearing, may assess the child's hearing. Specialized ear, nose, and throat surgeons may also work to repair the ear and any hearing issues. Often, these procedures are completed separately from other reconstructive procedures. 

Summary

Hemifacial microsomia is a birth defect that affects the development and appearance of the face. It impacts only one side of the face and may change the appearance of the eyes, nose, cheeks, jaw, ears, or mouth.

The exact cause is often unknown but is likely the result of genetic changes that take place during pregnancy. There is no cure for hemifacial microsomia, and possible treatments include surgery, orthodontic work, and audiology treatment.

A Word From Verywell

Learning that your child has hemifacial microsomia can be alarming and distressing. The vast majority of hemifacial microsomia cases are spontaneous and the exact cause may never be identified. Fortunately, many treatments, surgeries, and procedures have been developed to help correct hemifacial microsomia. These advances can help children with hemifacial microsomia live healthy and normal lives.