What Is Hemifacial Microsomia?
Hemifacial microsomia (HFM) is a condition present at birth in which the structures on one side of the face are smaller or less developed than the other side. The lower jaw (mandible) is the most commonly affected structure, but the condition can also involve the upper jaw (maxilla), the ear, the facial nerve, the muscles of chewing (muscles of mastication), and the soft tissue of the cheek.
The condition goes by several names in the medical literature, including craniofacial microsomia, first and second branchial arch syndrome, and oculo-auriculo-vertebral spectrum (when it occurs with eye and spine abnormalities). The term Goldenhar syndrome is used when hemifacial microsomia occurs together with vertebral anomalies and dermoid cysts near the eye.
In about 10% to 15% of cases, both sides of the face are affected (bilateral involvement), though one side is usually more severely underdeveloped than the other.
How Severity Is Classified
The most widely used classification system for hemifacial microsomia is the OMENS system, which evaluates five key structures affected by the condition.
- O (Orbit): Ranges from normal eye socket size to significantly reduced or displaced orbit
- M (Mandible): Ranges from a mildly small but normally shaped jaw to a severely underdeveloped or absent jaw joint (TMJ) and ascending ramus
- E (Ear): Ranges from a mildly small ear to a completely absent external ear with closed ear canal
- N (Nerve): Ranges from normal facial nerve function to complete paralysis of the facial nerve branches on the affected side
- S (Soft tissue): Ranges from mild soft tissue deficiency to significant underdevelopment of muscle and fat on the affected side
What Causes Hemifacial Microsomia?
The exact cause of hemifacial microsomia is not fully understood. Current research suggests it results from a disruption in the blood supply to the first and second branchial arches during early fetal development (around weeks 4 to 8 of pregnancy). These branchial arches are the embryonic structures that develop into the jaw, ear, and associated facial tissues.
Known Contributing Factors
While no single gene has been identified as the cause, several factors are associated with an increased occurrence of hemifacial microsomia.
- A vascular disruption (interruption of blood flow) during early embryonic development is the leading theory
- Most cases are sporadic, meaning they occur without a family history of the condition
- A small percentage of cases (approximately 2% to 5%) show familial patterns, suggesting a possible genetic contribution in some families
- Some studies have found associations with maternal diabetes and certain medication exposures during pregnancy, though the evidence is not conclusive
- The condition is slightly more common in males and tends to affect the right side more often than the left
Surgical Treatment Options
Treatment for hemifacial microsomia is tailored to the severity of the condition, the patient's age, and which structures are affected. Surgical correction may involve the jawbone, soft tissue, ear, or a combination of these areas. Most patients require multiple procedures staged over several years.
Distraction Osteogenesis
Distraction osteogenesis is a technique that gradually lengthens bone by making a controlled cut and then slowly separating the two segments using a device called a distractor. New bone forms in the gap as it is widened. For hemifacial microsomia, this technique is used to lengthen the underdeveloped side of the jaw to better match the other side.
This procedure can be performed in children as young as 5 to 7 years old, depending on the severity of the jaw asymmetry and its impact on breathing, feeding, or the developing bite. The distractor device remains in place for several weeks while the bone is gradually lengthened, then for an additional period while the new bone hardens.
Costochondral Rib Graft
For patients who are missing the jaw joint (temporomandibular joint) or have a severely underdeveloped condyle (the rounded top of the jawbone that forms the joint), a costochondral rib graft may be used. This procedure takes a small section of rib bone with its attached cartilage cap and transplants it to reconstruct the missing or deficient jaw joint.
The cartilage cap has growth potential, which is an advantage in growing children. However, the growth of the graft is unpredictable, and some patients may experience overgrowth or undergrowth that requires further correction.
Orthognathic (Jaw) Surgery
Orthognathic surgery is typically performed after facial growth is complete, usually around age 16 to 18 for females and 17 to 19 for males. It involves cutting and repositioning the jawbones to correct alignment and improve facial symmetry.
For hemifacial microsomia patients, this may include a bilateral sagittal split osteotomy to reposition the lower jaw, a Le Fort I osteotomy to level the upper jaw (which often develops a cant due to the asymmetric growth), or a combination of both. Orthodontic treatment before and after surgery is essential to align the teeth so the jaws fit together properly after repositioning.
Soft Tissue Correction
Even after the bony framework is corrected, the soft tissue on the affected side is often thinner and less developed. Several techniques are used to restore facial volume and symmetry.
Options include fat grafting (harvesting fat from another area of the body and injecting it into the face), free tissue transfer (microvascular flaps), and dermal fillers for minor volume deficiencies. Fat grafting often requires multiple sessions because the body reabsorbs some of the transferred fat over time.
Recovery and Long-Term Care
Recovery from hemifacial microsomia surgery varies depending on the specific procedures performed. Because treatment typically involves multiple surgeries over several years, patients and families should plan for an extended treatment journey.
Recovery From Distraction Osteogenesis
After distraction osteogenesis, the patient remains in the hospital for 1 to 3 days. Once home, the distractor device is activated daily (typically by a parent for younger patients), turning a screw that gradually separates the bone segments by about 1 millimeter per day. The active distraction phase lasts 2 to 4 weeks, followed by a consolidation phase of 6 to 12 weeks while the new bone hardens. The device is then removed in a second, shorter surgical procedure.
Recovery From Orthognathic Surgery
Recovery from jaw surgery typically involves 1 to 2 nights in the hospital, followed by 4 to 6 weeks of limited activity. A soft or liquid diet is required for the first 2 to 6 weeks, depending on the extent of the surgery. Swelling peaks around day 3 to 5 and gradually resolves over 2 to 3 months, though subtle swelling may persist for up to a year.
- Orthodontic treatment continues after surgery, with fine-tuning of the bite typically taking 6 to 12 additional months
- Regular follow-up imaging monitors bone healing and jaw position stability
- Physical therapy may be recommended to restore jaw range of motion and muscle function
- Long-term follow-up with the surgical team is important to monitor for relapse or asymmetric growth (in younger patients)
Cost of Hemifacial Microsomia Treatment
The total cost of hemifacial microsomia treatment depends on which procedures are needed, how many surgeries are required over time, and where treatment is performed. These figures are estimates and can vary significantly. Always request detailed cost estimates and insurance pre-authorization before each phase of treatment.
Individual procedures typically fall within these general ranges: distraction osteogenesis ($15,000 to $40,000 including the device, surgery, and device removal), costochondral rib graft ($20,000 to $50,000), orthognathic surgery ($20,000 to $60,000), and fat grafting ($3,000 to $8,000 per session). Many patients require some combination of these procedures over their treatment journey.
Insurance Coverage
Because hemifacial microsomia is a congenital condition that affects function (breathing, chewing, speaking), most medical insurance plans cover surgical treatment as medically necessary. However, coverage details vary, and some plans may require prior authorization or classify certain procedures (such as soft tissue augmentation) as cosmetic.
Working with the surgical team's insurance coordinator early in the treatment planning process can help ensure that prior authorizations are obtained and that families understand their out-of-pocket responsibilities before each surgery.
When to Seek Specialist Evaluation
Children with hemifacial microsomia benefit from early evaluation by a craniofacial team, even before surgical treatment is needed. Early involvement of specialists helps establish a treatment timeline, monitor growth, and address functional concerns like hearing loss or breathing difficulties.
Key Milestones for Evaluation
- At birth or during infancy: Initial craniofacial team evaluation to establish baseline severity and create a long-term treatment plan
- Age 3 to 5: Assessment of jaw growth and breathing function. Some children with severe airway narrowing may need early intervention.
- Age 5 to 7: Evaluation for possible early distraction osteogenesis if the jaw asymmetry is significant and affecting function or dental development
- Age 8 to 12: Orthodontic evaluation and planning for mixed dentition (combination of baby and adult teeth) management
- Age 14 to 18: Comprehensive surgical planning for definitive orthognathic surgery once growth is nearing completion
- Young adulthood: Final soft tissue procedures and any revision surgeries to optimize long-term results
Find a Craniofacial Specialist for Hemifacial Microsomia
Treatment for hemifacial microsomia should be managed by a multidisciplinary craniofacial team, typically based at a children's hospital or academic medical center. The team usually includes an oral and maxillofacial surgeon, a plastic surgeon or craniofacial surgeon, an orthodontist, an ENT (ear, nose, and throat) specialist, a speech-language pathologist, and an audiologist.
When seeking care, look for centers that are accredited by the American Cleft Palate-Craniofacial Association (ACPA). These teams have the experience, infrastructure, and multidisciplinary coordination needed to manage complex craniofacial conditions throughout childhood and into adulthood.
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