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What Is Micrognathia?

Reviewed by Dan Brennan, MD on April 22, 2021

Micrognathia is a condition in which the lower jaw is smaller than usual. It is also known as mandibular hypoplasia. Those with micrognathia are usually born with it, and it may cause babies to have feeding and breathing problems. Sometimes micrognathia will correct itself as the child grows. 

Causes of Micrognathia

Micrognathia can be a part of a genetic disorder, or it can happen because of a random mutation. Sometimes the cause remains unknown.

When a baby is in the womb, the jaw develops through a complex process. Several elements must grow separately and then fuse. The complexity of the process may make it more likely that something could go wrong.

Diagnosing Micrognathia in the Womb

Sometimes doctors detect micrognathia before a baby is born. They can see the jaw with ultrasound as early as 10 weeks if the baby's head is in the right position. Three-dimensional ultrasound may show the jaw more clearly.

Babies are diagnosed with micrognathia in the womb using two methods. Doctors can make a subjective judgment based on the appearance of the ultrasounds, or they can attempt to measure the jaw using the ultrasound images.

When doctors diagnose micrognathia in utero, the primary concern is whether or not the micrognathia is part of a larger genetic condition. Further testing, perhaps including genetic testing, may answer that question. With an accurate diagnosis, the health care team can offer the parents prenatal counseling and arrange better postnatal care for the baby.

Diagnosing Micrognathia After Birth

Micrognathia is most often diagnosed after a baby is born, usually by a craniofacial specialist, a doctor who specializes in the face and head. The doctor will look for other abnormalities that sometimes appear with micrognathia.

Although micrognathia is usually present at birth, it can appear later. Besides the appearance of the jaw, parents and health professionals should be alert to feeding difficulties and breathing problems, including noisy breathing and pauses in breathing. Difficulty sucking and swallowing may also accompany micrognathia, sometimes resulting in slow weight gain. 

Diagnostic testing often includes X-rays or CT scans. A sleep study can measure heart function, breathing, and brain function. It can also check oxygen levels.  

Treatment of Micrognathia

Sometimes an undersized jaw gets better by itself, so monitoring the child’s progress can be a form of treatment. If micrognathia corrects itself, it usually occurs when the child is between 6 and 18 months old. Other treatments can be surgical or non-surgical. They aim to keep the tongue from blocking the airway and otherwise ensure an adequate air supply.

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Non-Surgical Treatments

Doctors may prescribe different sleeping positions to keep a baby's airway open. A device called a nasopharyngeal tube can serve the same purpose. It is inserted into a nostril and through the mouth into the throat. 

You may know that some snorers use devices called CPAPs, which stand for continuous positive airway pressure. Children with micrognathia can use similar machines to improve their air supply.  

Surgical Treatments

Three main surgical procedures are available for children with micrognathia:

Tongue-lip adhesion. This surgery attaches the tongue differently to the lower jaw so that it can't obstruct breathing.  

Mandibular distraction osteogenesis (MDO). A surgeon makes cuts in the lower jawbone on both sides. He inserts devices that spread the gaps apart, promoting bone growth in the space. This surgery carries some risks, such as infection and nerve damage, but it can improve the airway in a matter of weeks.

Tracheostomy. In this procedure, doctors make a hole in the neck and insert a tube into the windpipe to create an airway. Tracheostomies require careful tending and sometimes frequent suctioning. One reason for performing an MDO is that it may allow children with micrognathia to avoid having a tracheostomy.

Syndromes Associated With Micrognathia

There are several syndromes that have micrognathia as a symptom, including these: 

Pierre Robin sequence. This condition is called a sequence because the sequence of development in the womb is disrupted. The undersized jaw pushes the tongue back and may keep the palate from closing, creating a cleft palate. Pierre Robin is one of the most common conditions associated with micrognathia, occurring once in every 8,500 births. It can be mild or more serious. 

Treacher Collins syndrome. This syndrome causes the bottom half of the head to be underdeveloped, including the jaw, palate, cheekbones, and mouth. The eyes and ears may be affected. Some cases are serious. Others are so mild that the child is never diagnosed. Treacher Collins could occur as often as once in 10,000 children, or it could be rarer. Undiagnosed cases make it hard to tell.

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Stickler syndrome. Children with Stickler syndrome have abnormal collagen, which is the fibrous protein that connects and supports the body's tissues. They commonly have problems with facial features, eyes, ears, and joints. They may have a long list of symptoms or just one or two. Stickler syndrome may occur as often as once in 7,500 people, but many cases go undiagnosed.

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Hemifacial microsomia. In this condition, one side of the face is underdeveloped. Hemifacial microsomia is the most common facial birth defect except for cleft lip and palate. It occurs about once in 4,000 births. It goes by several other names, such as craniofacial microsomia.

If you think you or your child may have Micrognathia, talk to your doctor about getting a diagnosis and discussing what treatment options would be best for you. 

WebMD Medical Reference

Sources

SOURCES:

American Academy of Pediatrics: "Micrognathia & Pierre Robin Sequence." 

American Journal of Medical Genetics: "Prenatal diagnosis of micrognathia in 41 fetuses: Retrospective analysis of outcome and genetic etiologies." 

Boston's Children's Hospital: Stickler Syndrome Symptoms & Causes." 

Children's Hospital Colorado: "Micrognathia."

Children's Hospital of Philadelphia: "Hemifacial Microsomia," "Micrognathia." 

Children's Wisconsin: "Micrognathia and Pierre Robin Sequence." 

National Organization for Rare Disorders: "Treacher Collins Syndrome." 

ULTRASOUND in Obstetrics and Gynecology: "Fetal micrognathia: almost always an ominous finding."

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