What is Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)?
Hemifacial microsomia (HFM), also called unilateral otomandibular dysostosis or lateral facial dysplasia, is a condition that people are born with, where one side of the face is smaller than the other. It involves the 1st and 2nd branchial arches (areas developing into parts of the face, neck, and throat). This is the second most common facial abnormality after a cleft lip and palate, which are openings or splits in the mouth roof and lip.
People with this condition often have a smaller ear on one side, the facial skeleton (jawbone, cheekbone, and temples), and the tissue near these bones. HFM is closely related to Goldenhar syndrome, and they both fall under the category of oculoauriculovertebral spectrum (OAVS) disorders. Goldenhar syndrome includes features of HFM but also includes specific eye (epibulbar dermoid) and spine (vertebral) abnormalities.
What Causes Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)?
Hemifacial microsomia (HFM) is a condition that affects the development of the face and is connected to issues with the tissues and structures inside the face and neck, known as the 1st and 2nd branchial arches. These are made from certain cells called neural crest cells, yet the reasons for HFM are unclear.
There are two main theories currently being explored. One suggests that damage to an artery in the face, called the stapedial artery, could be the cause. Another theory considers improper migration of neural crest cells as the culprit.
The different ways HFM can look in different people (its ‘heterogenous phenotypical appearance’) might be due to a mix of genes and environmental factors disrupting the development of these branchial arches. These developing arches are mediated by blood vessels, and they typically form during the first 4 weeks of pregnancy.
To understand better, during development, the first branchial arch ultimately forms major parts of the face, like the upper and lower jaws and major muscles and nerves responsible for chewing. The rest, like the hyoid bone and muscles for facial expression, are formed by the second branchial arch.
Disturbances in the growth of these arches can be caused by many factors including genetics, harmful external influences such as medications or drugs, smoking, hormonal therapy, or injury. Certain conditions in the mother, such as diabetes, hypothyroidism, or celiac disease, can also impact the development.
Specific genetic mutations and chromosomal abnormalities, for example, trisomy 10p, 12p13.33 microdeletion, 22q11.2 microdeletion, large 5p deletion, and 10.7 cM on chromosome 14q32, are also associated with HFM.
Risk Factors and Frequency for Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)
Hemifacial microsomia (HFM) is the second most common birth defect affecting the face and skull, only after cleft lip and palate. Usually, HFM happens randomly with no prior family history. However, some studies propose it may be genetically passed down in families. In the United States, it’s estimated to occur in between 1 in 3500 to 1 in 5600 babies.
- Hemifacial microsomia (HFM) is the second most common birth defect of the face/skull, following cleft lip and palate.
- Most cases occur randomly and are not inherited.
- It affects between 1 in 3500 to 1 in 5600 babies in the United States.
- Some studies show it’s more common in males and usually affects the right side, but other studies found no such patterns.
- There’s a 10% chance it can affect both sides of the face, mostly in cases where it’s inherited.
Signs and Symptoms of Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)
When examining a child for HFM, or Hemifacial Microsomia, a thorough family history is needed. This should span three generations to pinpoint any distinguishing features linked to HFM. It’s also important to gather details on the mother’s health and habits during pregnancy, like if she had gestational diabetes, an underactive thyroid, or used any medications or drugs. Particular attention should be given to any issues the child may have with sleep, eating, swallowing, and their speech development.
The physical examination should pay special attention to any irregularities in the child’s face. These could include differences or asymmetries in:
- The auricle (external part of the ear)
- The ossicles (tiny bones in the middle ear)
- The zygoma (or cheekbone area)
- The maxilla (upper jaw)
- The mandible (lower jaw)
- Jaw movement
- Teeth alignment (occlusion)
Naturally, seeing cleft lip and palate – common in children with HFM – is important. Likewise, conditions like ocular dermoid cysts (cysts in the eye) and scoliosis (curvature of the spine) could mark a more severe form of HFM known as Goldenhar syndrome.
Testing for Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)
To diagnose Hemifacial Microsomia (HFM), a condition that affects the development of the lower half of the face, doctors look for either 1) defects in the jaw and outer ear on the same side or 2) unevenness in the jaw or outer ear along with two or more indirectly associated issues or a family history of HFM.
A specific type of X-ray called the posteroanterior cephalogram is the best way to assess any facial asymmetry. This analysis gives doctors crucial measurements, such as the alignment and heights of the jaw, which helps them plan any necessary surgery. Photos are also taken throughout the treatment to monitor progress. Computer Tomography (CT) scans, which are a series of X-ray images from different angles, can also be used to examine the ear ossicles (the tiny bones in your ear), the space within the middle ear, and the form and size of facial bones. These scans can even help create 3D models of the facial skeleton, which can guide the placement of surgical devices.
Many patients with HFM face issues with their airway and feeding because of underdeveloped areas in the throat, larynx (voice box), esophagus (food tube), jaw, and chewing muscles. Conditions like obstructive sleep apnea (a sleep disorder where breathing stops and starts), difficulty swallowing, and cleft lip and palate (a gap in the upper lip or roof of the mouth) are diagnosed in a significant percentage of patients with craniofacial malformations. Therefore, patients with HFM, particularly those with a small jaw and symptoms of obstructive sleep apnea, should undergo sleep studies (polysomnography) and have their swallowing checked by a speech-language pathologist.
Additional tests include an audiogram to look for hearing loss, an analysis of speech development, and an emotional and social evaluation. X-rays of the neck spine for vertebral defects and an ultrasound of the kidney for issues not related to facial structures are also recommended. When a genetic component is suspected, families can also be offered chromosomal analysis and genetic counseling.
Treatment Options for Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)
Hemifacial Microsomia (HFM) is a condition that affects the development of the face and skull, resulting in differences in structure and appearance on one side of the face. Because the symptoms and severity of HFM can vary so much from person to person, each patient needs a unique, well-coordinated plan of care. It’s especially important to address any problems with breathing or swallowing first, as HFM can sometimes cause complications in these areas, due to underdevelopment of parts of the face and jaw. In severe cases, a surgical procedure known as a tracheotomy may be necessary to secure a clear airway. Babies with swallowing difficulties might need a feeding tube.
Reconstructive surgery for HFM aims to improve facial symmetry, jaw function, and teeth alignment. The type of surgery will likely depend on how severe the facial differences are. Here are some of the surgical options:
Grafts involve taking bone or cartilage from one part of the body and using it to augment the underdeveloped side of the jaw. However, complications can include infection, impaired joint movement, potential fracture, degradation of the graft material, and recurrence of asymmetry.
Mandibular Distraction Osteogenesis (MDO) is a procedure that expands the jaw by slowly extending its length. This method encourages new bone growth in the jaw, and generally results in fewer complications and high levels of improvement for patients.
While newer internal MDO devices have shown to provide superior mechanical strength, there are possible disadvantages, such as the need for a second operation for device removal, scarring, hardware malfunction, improper distraction, injury to teeth or jaw joint, nerve injury, infection, and excessive bone growth over the devices.
Soft tissue corrections are generally performed after the alignment of the facial skeleton has been addressed. Methods to enhance surrounding tissue may include the transfer of tissue from one body part to another, fat grafting, or the use of implants.
Ear reconstruction can also be a part of treatment for HFM, as it can cause differences in the structure and appearance of the ear. Techniques can range from reshaping existing ear cartilage, to grafting or synthetic implants for more significant alterations. For those with more profound deformities, a prosthetic ear may be the most suitable option.
Overall, while HFM can propose challenges, there are a variety of treatment options available to help ensure each person can live a normal, healthy life. Coordinating with a team of healthcare professionals to come up with an individualized treatment plan is crucial.
What else can Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia) be?
Hemifacial microsomia is a medical condition involving facial defects, which can vary greatly in how severe they are. It can sometimes be confused with other disorders that also cause facial irregularities. Here are several such disorders:
- CHARGE syndrome
- Restricted growth and development
- Treacher Collins syndrome
- Townes-Brocks syndrome
- Goltz syndrome
- Pierre Robin syndrome
- Traumatic postnatal deformity
- Parry-Romberg syndrome
- Juvenile rheumatoid arthritis
- Nager acrofacial dysostosis syndrome
- Branchio-oto-renal syndrome
- Maxillofacial dysostosis
What to expect with Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)
Research has shown that the use of internal devices in a specific type of jaw surgery, known as mandibular distraction osteogenesis, can effectively lengthen the jaw (mandible) and improve aspects like facial balance, attractiveness and teeth alignment. This conclusion is based on post-surgery image analysis.
That being said, there is a lack of long-term data regarding these surgeries. One specific study observed patients for a period between 1 and slightly over 7 years post-surgery and found that 51% to 100% of these patients experienced a return of their original jaw length and facial balance or symmetry during the 42 to 92 months duration.
This significant portion of patients who experienced a regression in their symptoms needing a further corrective operation shows the necessity for continued monitoring and care. A 2012 research document further confirms this view, suggesting that the uneven facial proportions and growth patterns observed in patients with HFM, a facial growth disorder, are likely due to genetic factors. Furthermore, these proportions and patterns may bounce back to their pre-surgery state even after the jaw lengthening procedure.
Families and patients considering this kind of surgery should be made aware that there’s a very high chance that repeat surgery may be needed as the patient grows and develops throughout childhood and adolescence.
Possible Complications When Diagnosed with Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)
The treatment of choice for patients with Hemifacial Microsomia (HFM) is known as mandible distraction osteogenesis. However, this comes with certain complications and difficulties. According to a widespread review by Verlinden and colleagues, complication rates were found to be almost 44%. Out of these, around 14% needed additional surgery, hospitalization, or led to lasting health problems. Depending on the individual case, nerve injuries—in particular to the inferior alveolar nerve or mental nerve—happened in 4.2% to 37.5% of patients.
Problems with the mucosal and soft tissue can happen in 1.6% to 3.1% of instances, often because of the thin soft tissue that covers the underdeveloped bone. The mylohyoid muscle’s traction on the bone segment that has been cut can cause lingual displacement, meaning the tongue is moved from its natural position, in 7.6% of patients.
Other complications include the mandible not aligning properly (0.6% of cases), and mandible fractures occurring in 2.8% of the examined patients. Additional complications ranged from the bones not properly bonding, inadequate bone formation, hardware exposure, facial scars, infections at the wound site, and in extreme cases, decay and death of the mandible tissue itself.
Outlined Complications:
- Nerve injuries to the inferior alveolar nerve or mental nerve (4.2% to 37.5% of patients)
- Mucosal and soft tissue problems (1.6% to 3.1%)
- Tongue displacement (7.6% of cases)
- Mandible not aligning properly (0.6% of cases)
- Mandible fractures (2.8% of cases)
- Bones not properly bonding
- Inadequate bone formation (less common)
- Exposure of the hardware used in surgery
- Facial scarring
- Infection of the incision site
- Decay and death of mandible tissue
Recovery from Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)
Once the surgeon places devices inside the body to slowly change the shape or position, patients stay in the hospital for monitoring of their breathing. They are allowed to return home when they can comfortably breathe and eat without any problems. For school-aged kids, there’s a wait of about 4 to 7 days before these devices, called distractors, are started up. They are adjusted to extend by 1 millimeter per day until the desired result is achieved, which was planned before the surgery. Parents learn how to make these adjustments and how to keep the surgical area clean at home.
When the bone reformation is finished, any parts of the machines poking out of the skin are removed. After another 2 to 3 months, the patient comes back to the hospital for another operation to remove the internal parts of the device. To track the success of the treatment, pictures (known as cephalograms) are taken at key points: when the adjustments start, once they’re complete, before the device removal, and then a year after the operation.
Preventing Hemifacial Microsomia (Unilateral Otomandibular Dysostosis or Lateral Facial Dysplasia)
Explaining hemifacial microsomia, a condition that affects the development of one side of the face, can be difficult due to the various ways it can present and the need for a team of experts in different areas for treatment. It’s important to engage a speech therapist early on to help with any difficulties with speaking and swallowing. Meeting with a genetic counselor can offer valuable insights into potential genetic or chromosomal irregularities in the family.
It’s crucial for patients and their families to understand the various treatment choices, as well as the timeline for surgeries to rebuild facial features. There’s notable evidence suggesting that an uneven growth of the bones on one side of the face can reoccur following initial surgery. Often, it’s recommended to delay surgery until the patient’s skeleton and teeth fully mature to avoid the need for repeated surgery in the future.
Yet, it’s also crucial to consider how having noticeable and functional impairments for an extended period can significantly affect a child’s social development and personality formation. So, it’s vital for patients and parents to weigh the benefits and drawbacks of having surgery at an early age to give the child a more normal childhood, but with the understanding that further corrective surgery might be required in the future versus waiting for surgical intervention. This ensures a well-informed decision is made, taking into account the child’s well-being.
