Hemifacial Microsomia 

Overview

Children born with hemifacial microsomia require a team of highly experienced physicians, surgeons, and health care providers to properly manage the issues associated with this condition. Facial reconstructive procedures should be performed by experienced craniofacial surgeons in order to achieve the best possible outcomes. The surgeons at our center have an extensive knowledge of hemifacial microsomia and are an integral part of the New Jersey Institute for Craniofacial Surgery functioning as Craniofacial Surgeons, Plastic & Reconstructive Surgeons, and Oral & Maxillofacial Surgeons for the Institute. Members of our team have led the center for more than 30 years.

 

Hemifacial microsomia is the second most common facial birth defect behind cleft lip and palate, affecting approximately 1 in every 3,500 to 5,600 to births.

 

Five major areas are affected by hemifacial microsomia:

  1. External ear

  2. Mandible (lower jaw)

  3. Orbit (eye bones)

  4. Facial nerve (the nerve controlling the muscles of facial expression)

  5. Facial soft tissues (muscle, subcutaneous tissues, fat, and skin)

 

Traditionally hemifacial microsomia occurs on only one side of the face (hemifacial); however, in 10 to 15 percent of cases, it may occur on both sides of the face. When it occurs on both sides of the face, it is referred to as craniofacial microsomia.

  • Hemifacial microsomia may be referred to by many names, including:

  • First and second branchial arch syndrome

  • Otomandibular dysostosis

  • Facio-auriculo-vertebral syndrome

  • Oculo-auriculo-vertebral spectrum

  • Lateral facial dysplasia

 

Hemifacial microsomia is commonly confused with Goldenhar syndrome. However, Goldenhar syndrome is a separate entity of which hemifacial microsomia is just one of the characteristics. Goldenhar syndrome is a rare congenital condition that also includes vertebral anomalies and epibulbar dermoids appearing as “skin patches” that extend onto the conjunctiva and cornea of the eye.

 

Etiology (Cause)

It is unclear exactly what causes hemifacial microsomia. It is believed that the process begins in the first trimester of pregnancy. The facial anomalies are not caused by something the mother did or something she ate; it usually just happens by chance. In a small number of cases, a child inherits the condition from his or her parents. An adult with hemifacial microsomia has about a 3% chance of having a child with the same condition.

Initially it was believed that this disorder was caused by an interruption of the blood supply (stapedial artery) to the affected side of the face. In the early 1970s, Dr. David Poswillo developed this theory by administering various medications to mice and monkeys and noting a disruption of the blood supply in a focal area of the face that led to the development of characteristics consistent with hemifacial microsomia in 100% of the animals.

However, now it is believed that hemifacial microsomia most likely occurs as a result of a disruption in the migration of neural crest cells. Dr. Malcolm Johnston and Dr. Peter Barsky developed this theory and proposed that the failure of migration of the various neural crest cells leads to both the diversity and variability seen in hemifacial microsomia.

In a recent study by Tuin, it was determined that although there is variability in the degree of deficiency in each of the affected facial structures, those developed from the first branchial arch (orbit, mandible, and soft tissue) are similar in degree of deficiency, as are the structures derived from the second branchial arch (facial nerve and ear).

 

Characteristics

Characteristics of hemifacial microsomia range from very mild to severe. A child with a mild form of hemifacial microsomia may have an unnoticeably smaller jaw and a skin tag in front of a normal appearing ear. In more severe forms, a child may present with a significantly deficient and asymmetrical jaw on the affected side in addition to a small orbit (eye socket), missing ear, lack of soft tissue, and decreased function of the facial muscles on the affected side. 


 

 

Figure 1 Variable Malformations Associated with Craniofacial Microsomia

 

Several classification systems exist to describe which structures are affected and to what degree. The most common systems are the OMENS and the Pruzansky/Kaban classification systems. For more information regarding these classification systems, refer to Hemifacial Microsomia Classification Systems.

 

Treatment

As is the case for any patient with a complex craniofacial deformity, individual treatment varies depending upon the degree of involvement of the various structures. Possible treatments include the following.

 

Breathing-related treatments in infancy
  • Positioning

  • Tongue lip adhesion

  • Distraction of the mandible

  • Tracheostomy

 

Correction of fronto-orbital deficiencies
  • Correction of the forehead and orbit (eye bones) on the affected side

Correction of a deficient or absent ear
  • Reconstruction of an absent or malformed external ear

 

Functional orthodontics
  • May be required to correct and prevent further maxillary (upper jaw) asymmetry

 

Corrective jaw surgery/distraction
  • Corrective jaw surgery is typically required in moderate to severe cases. In certain circumstances, a rib graft or a process referred to as distraction osteogenesis may be recommended in order to achieve optimal results.

 

Custom facial implants
  • May be required in addition to the above procedures in order to achieve the best aesthetic results

 

Because multiple structures may be involved in hemifacial microsomia, continued monitoring is important. Facial growth should be monitored throughout childhood and adolescence, adjusting the treatment plan as necessary.

 

References

Horgan JE, Padwa BL, LaBrie RA, et al. OMENS-Plus: analysis of craniofacial and extracraniofacial anomalies in hemifacial microsomia. Cleft Palate Craniofac J. 1995;32:405-412.

Grabb W: The first and second branchial arch syndrome. Plast Reconstr Surg. 1965;36:485-508.

Johnston M, Bronsky P. Prenatal craniofacial development: new insights on normal and abnormal mechanisms. Crit Rev Oral Biol Med. 1995;6:368.

Poswillo D. Hemorrhage in development of face. In Bergsma D, ed. New York: Alan R. Liss, 1975:61-81.

Poswillo D: The pathogenesis of the first and second branchial arch syndrome. Oral Surg Oral Med Oral Pathol. 1973;35:302-328.

Tuin AJ, Tahiri Y. Clarifying the relationships among the different features of the OMENS+ classification in craniofacial microsomia. Plast Reconstr Surg. 2015 Jan;135(1):149e-156e.

 

Image Reference

Figure 1: GeneReviews®. Pagon RA, Adam MP, Ardinger HH, et al., eds. Craniofacial Microsomia Overview., GeneReviews® [Internet]. Seattle, WA: University of Washington, Seattle, 1993-2015. Copyright © 1993-2015, University of Washington, Seattle. All rights reserved.

 

Classification

Many classification systems have been developed to help categorize and treat the severity of the hemifacial microsomia patients. The two most popular classifications, and the most clinically useful ones, are Dr. Samuel Pruzansky’s classification of the mandibular (lower jaw) anatomy, with a modification by Dr. Leonard Kaban, and the OMENS classification developed by Dr. John Mulliken, which helps to determine which facial features are involved and to what degree. Below is a description of the Pruzansky/Kaban Classification.

 

Pruzansky/Kaban Classification of Mandibular Deficiencies

Type I – Mandibles are essentially normal in shape and morphology; however, they are small when compared to the opposite “normal” side.

 

Type IIa – Mandibles have an abnormal shape and morphology, but the TMJ is functional and appropriately positioned to allow for “symmetrical opening of the mandible.”

 

Type IIb – Mandibles have an abnormal shape and morphology with the TMJ malpositioned inferiorly, medially, and anteriorly, rendering it nonfunctional.

 

Type III – Mandibles are missing the TMJ (ramus and glenoid fossa), with essentially no mandibular development behind the teeth.

 

 

References

Kaban L, Moses M, Mulliken J. Surgical correction of hemifacial microsomia in the growing child. Plast Reconstr Surg. 1988;82: 9-19.

Pruzansky S. Not all dwarfed mandibles are alike. Birth Defects. 1969;4:120.

Vento A, LaBrie R, Mulliken J. The OMENS classification of hemifacial microsomia. Cleft Palate-Craniofacial J. 1991;28:68-77.

 

Treatment

Functional Orthodontics 

 

Orthodontics in children with facial clefts and facial asymmetry is a unique specialty of orthodontics involving functional orthodontics. Functional orthodontics is a specialized form of orthodontics that can help to correct not only the position of the teeth, but also the position and function of the jaws. This type of orthodontics is particularly important in children with facial clefting and facial asymmetry because it can help to prevent or lessen some of the more common irregular jaw relationships that may develop.

 

Functional orthodontics is a way of tricking the teeth and jaws to grow and develop in a planned manner. Functional orthodontics can create space for teeth and jaws to grow by using various types of appliances, retainers, and dental adjustments. In children with hemifacial microsomia, the deficient lower jaw is canted and occupying the space where the teeth of the upper jaw would normally be positioned. This prevents the teeth and bones from developing into this area, resulting in a canting of the upper jaw and an asymmetrical appearance. Sometimes by placing an appliance between the upper and lower teeth on the opposite side, a space can be created on the affected side, allowing the upper teeth and bone to grow into a more normal position. Once the teeth move into the space, they will maintain it and prevent further distortion.

 

Typically, functional orthodontics cannot be performed until the permanent molars have erupted (around 6 years of age). It is important to be evaluated by an orthodontist with experience in treating children with hemifacial microsomia so that intervention can be made at the appropriate time. If intervention is delayed, certain opportunities may be missed.

 

Rib Graft Harvest Procedure

 

It may be necessary to utilize rib grafts in children for ear reconstruction, nasal reconstruction, or reconstruction of the lower jaw.

 

Rib graft harvest is a commonly performed procedure in craniofacial surgery. It provides the best source of firm cartilage necessary for ear, nasal, and lower jaw reconstruction.

 

Jaw Surgery

 Corrective jaw surgery for patients with hemifacial microsomia is a unique subspecialty of corrective jaw surgery. A thorough understanding of the causes, treatment options, variations, and surgical procedures is necessary to provide comprehensive treatment. Surgical execution of the required procedures should be performed by a facial reconstructive surgeon experienced in complex jaw reconstructive procedures in order to achieve the best outcome. All of the surgeons at our center have an extensive knowledge of hemifacial microsomia and are an integral part of the New Jersey Institute for Craniofacial Surgeryfunctioning as Craniofacial Surgeons, Plastic & Reconstructive Surgeons, and Oral & Maxillofacial Surgeons for the Institute. Members of our team have led the center for more than 35 years.

 
Key Points

Some key points to understand that are unique to jaw surgery for hemifacial microsomia are:

 

  1. Although the primary disturbance is in the mandible (lower jaw), secondary disturbances in the maxilla (upper jaw) typically require correction as well.

  2. An understanding of the comprehensive treatment plan is necessary. Proper planning of incisions is critical to avoid damaging blood supply necessary for future ear and soft tissue reconstructions. Improper placement of incisions can compromise future reconstructions.

  3. The mandible (lower jaw) is typically deficient in size, shape, and position. Therefore, simply repositioning the jaw may not be enough and further augmentation may be required.

 

Jaw Surgery

There is much variation in the treatment of jaw abnormalities related to hemifacial microsomia ranging from treatment using only a custom facial implant to treatment requiring reconstruction of the maxilla (upper jaw), mandible (lower jaw), TMJ, chin, and placement of custom facial implants.

 

Early vs. Late

In more severe cases, some surgeons recommend surgery at a young age while the lower jaw is still growing to avoid secondary disturbances in the maxilla (upper jaw). These procedures are followed by a second definitive jaw surgery procedure when facial growth is completed.

 

Other surgeons recommend functional orthodontics during facial growth followed by jaw surgery only after facial growth is completed.

 

At our center, we follow a more conservative approach of avoiding surgery until facial growth is completed if at all possible. We have had great success using functional orthodontics to minimize secondary disturbances to the maxilla.

 

Jaw Surgery after Facial Growth Is Completed

Once facial growth is completed, an appropriate treatment plan can be determined. Treatment is based on the following factors:

  1. The size, shape, and volume of the mandible on the affected side

  2. The amount of secondary disturbance of the maxilla (upper jaw)

  3. The anatomy of the condyle and TMJ (Pruzansky/Kaban classification)

Most cases will require correction of the maxilla (upper jaw), mandible (lower jaw), and chin.

 

Cases in which the anatomy of the condyle and TMJ produce improper function (Pruzansky/Kaban type IIb and III) may require additional procedures to reconstruct the condyle and TMJ. Correction in these situations may be achieved using either one or more of the following techniques:

 

  • Rib graft reconstruction to create a new condyle on the affected side

  • Distraction osteogenesis to create a new condyle and to “grow” bone in the affected area. (For more information please visit our distraction osteogenesis portal.)

  • Custom-fabricated prosthetic titanium TMJ and condyle

  • Custom facial implants

 

References

McCarthy JG, Schreiber JS, Karp NS, et al. Lengthening of the human mandible by gradual distraction. Plastic Reconstr Surg. 1992;89:1.

Meurmann Y. Congenital microtia and meatal atresia. Arch Otolaryngol. 1957;66:443.

Molina F, Ortiz-Monasterio F. Mandibular elongation and remodeling by distraction: a farewell to major osteotomies. Plast Reconstr Surg. 1995;96:825.

Mulliken JB, Kaban LB. Analysis and treatment of hemifacial microsomia in childhood. Clin Plast Surg. 1987;14:91.

Munro IR, Lauritzen CG. Classification and treatment of hemifacial microsomia.

In: Caronni EP, ed. Craniofacial Surgery. Boston: Little, Brown, 1985:391-400.

Obwegeser HL. Correction of the skeletal anomalies of otomandibular dysostosis. J Maxillofac Surg. 1974;2:73.

Vento AR, La Brie RA, Mulliken JB. The O.M.E.N.S. classification of hemifacial microsomia. Cleft Palate Craniofac J. 1991;28:68.

Please visit  The Amato Center for more information on Hemifacial Microsomia at:

https://www.theamatocenter.com/hemifacia-microsomia

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