Micrognathia

Micrognathia or micrognathism is a condition where the lower jaw is abnormally small. It’s usually something a child is born with.

Micrognathia often leads to complications such as difficulty breathing, problems with eating, and malocclusions. Some cases improve or completely resolve with time as the child grows up. 

Technically, a small upper jaw (maxilla) can also be referred to as (maxillary) micrognathia. However, in this article, we’ll focus on the lower jaw.

What Causes Micrognathia?

Micrognathia is usually present at birth (congenital). It can sometimes develop after a baby is born due to trauma or infection affecting the jaw joint.

Congenital micrognathia often occurs as part of a birth defect called Pierre Robin sequence (PRS). PRS is known as a sequence because these issues seem to develop in a particular order, starting with micrognathia.

One study found that about 40% of people had PRS alone, with the other 60% having syndromic PRS, meaning they had other conditions associated with PRS.

Other risk factors for micrognathia include:

• Stickler syndrome — Affects the collagen in connective tissues, resulting in abnormal facial features, vision and hearing problems, and extreme joint mobility.
• Treacher Collins syndrome — Affects the cheekbones, jaw, ears, and eyelids.
• Hemifacial microsomia — A similar congenital condition that affects only one side of the face.
• DiGeorge syndrome — Causes micrognathia in addition to heart defects, immune deficiency, and other problems.

Symptoms of Micrognathia

Those with micrognathia have small jaws, including a small or recessed chin. A recessed chin can also be caused by retrognathia, where the lower jaw is of normal size but is further back than usual.

Babies with micrognathia can also have other symptoms, including:

• Trouble feeding, leading in some cases to poor weight gain
• Breathing problems, including episodes of apnea
• Poor sleep due to sleep apnea
• Tongue retraction

Tongue retraction and a cleft palate are also associated with micrognathia as part of PRS. If micrognathia or PRS occurs as part of a syndrome, other symptoms may be present, such as other abnormal facial features or skeletal, muscular, or organ issues.

How is Micrognathia Treated?

Treatment for micrognathia varies depending on severity and the presence or absence of an underlying syndrome. In severe cases, surgery may be necessary.

Conservative Treatment

Micrognathia can often be treated without surgery. This is especially likely if it occurs on its own and not as part of a syndrome.

Non-surgical treatment focuses on managing breathing problems. For example, babies may be kept on their stomachs or sides to let gravity pull the tongue forward and improve airflow.

Additionally, special equipment, such as continuous positive airway pressure (CPAP) machines, can improve breathing in children with micrognathia.

Surgical Treatment

Surgery may be required in more severe cases of micrognathia. For example, syndromic PRS is much more likely to require surgery than isolated PRS.

There are a few possible surgeries your doctor can choose to do, depending on the case.

• Tongue-lip adhesion ⁠— It’s the least invasive option and prevents the tongue from falling back and making breathing difficult. It can be temporary in cases where the lower jaw catches up in growth over time.
• Mandibular distraction osteogenesis⁠ — This lengthens the lower jaw by breaking the bone at specific points and allowing new tissue to grow as it heals. 
• Tracheostomy⁠ — This is more likely to be performed if the airway is obstructed in multiple places. The procedure creates an opening in the windpipe and front of the neck to allow breathing without using the nose or mouth. 

All of these surgeries come with potential complications, including infection and damage to surrounding tissues.

What’s the Outlook for Micrognathia?

The long-term outlook for babies with micrognathia depends on the underlying cause and accompanying issues. In many cases of micrognathia, the mandible may grow during childhood or puberty to catch up with the rest of the face. 

Feeding and breathing problems will eventually go away in these cases. However, if micrognathia occurs as part of a syndrome such as Treacher Collins, the child can grow up healthy, perhaps with corrective surgery.

Some syndromes that cause micrognathia, such as trisomy 18 (Edwards syndrome), have a poor long-term prognosis. With this condition, most babies don’t survive infancy.