Hemifacial Microsomia: Clinical Characteristics, Complications, and Reconstructive Modalities

What Are the Features of Hemifacial Microsomia?

Hemifacial microsomia (HFM), also termed in medical research and literature as the condition of unilateral otomandibular dysostosis or lateral facial dysplasia, is a congenitally acquired craniofacial condition. This is an asymmetrical, congenital malformation that manifests from the embryologic disturbance of the 1st and 2nd branchial arches and is known as the second most common craniofacial disease or genetic anomaly that can occur in newborns, next only to cleft lip and palate (that are the most common congenital malformations). Patients or newborn children that present clinically with features of hemifacial microsomia or HFM are as follows:

A. Unilateral hypoplasia is present in the ear and the facial skeleton.

B.Unilaterally, hypoplasia is present in the parts of the upper jaw or maxilla, lower jaw or mandible, zygoma, temporal bones of the skull, etc, and may extend further to the surrounding soft tissues.

What Is the Diagnosis and Hypothesis Behind Hemifacial Microsomia Disease Occurrence?

Though many physicians may commonly confuse the HFM to be different from the Goldenhar syndrome, it is to be noted that these are, in fact, only variants of a craniofacial manifestation that occurs in the affected individuals. HFM and Goldenhar syndrome belong to the same clinical classification of craniofacial disorders termed the oculoauriculovertebral spectrum (OAVS), with the patients of Goldenhar syndrome usually having more vertebral anomalies, in comparison to Individuals affected by HFM. HFM is a craniofacial dysfunction that can be attributed to the pathogenesis that occurs in the 1st and 2nd branchial arches. These branchial arches are formed by the neural crest cells (NCC) in the embryo. The cause of HFM is exactly uncertain according to medical research and literature, but there exist two major theories that can possibly explain this pathogenesis of the branchial arches.

While the first hypothesis is of a vascular injury of the stapedial artery in the embryo leading to HFM manifestations in newborn, the second theory is of the migration of the neural crest cells away from their origin, resulting in the congenital malformations of the craniofacial cavity, due to the physical disturbance from the first and second branchial arches.

What Is the Etiology and Pathogenesis of Hemifacial Microsomia?

Some medical research also shows that this disease is a heterogeneous phenotype that is inherited and can be mainly due to a combination of genetic and environmental factors that disrupt the normal vascularization and development of the first and second pharyngeal arches. The first and second pharyngeal arches are formed and vascularized during the first four weeks of pregnancy, that is, in the first month of pregnancy after the embryo is fertilized and continues to develop.

Embryonically, the first branchial arch gives rise to the structures of the upper jaw or the maxilla, lower jaw or mandible, the zygomatic arch of the face, all the muscles of mastication or the chewing muscles of the face, the cranial nerve V or the trigeminal nerve, the anterior auricle (tragus, helical root, helix), the malleolus, and incus bones. The second branchial arch on the other hand gives rise to the structures of the hyoid bone, all the major muscles of facial expression, Cranial nerve VII or the facial nerve, stapes, and a remainder portion of the auricle (antihelix, antitragus, and lobule).

An embryonic disturbance or disruption during this pharyngeal arch development can be either because of genetic defects, hypothyroidism conditions, teratogenic causes, smoking during pregnancy, as a result of hormonal therapies, vascular injury, vasoactive medications, cocaine, maternal type 2 diabetes infection, or celiac disease- that can eventually result in the craniofacial hypoplasia.

What Are the Chromosomal Abnormalities, Familial Inheritance, and Incidence of Hemifacial Microsomia?

Current medical research also attributed that newborns with HFM can be a result of genetic mutations and chromosomal abnormalities such as the 5pcM deletion,10.7 cM on chromosome 14q32, trisomy 10p, 12p13.33 microdeletion, 22q11.2 microdeletion, etc. The cases of HFM are usually sporadic, meaning that the familial inheritance pattern exists from autosomal dominant and recessive inheritance. The approximate incidence of HFM is 1 in 3500 to 1 in 5600 live births, as per research reports conducted in the last decade in the United States. Certain medical studies have reported a very high 10 percent chance of bilateral presentation of these craniofacial features, commonly in genetic cases of autosomal dominant inheritance.

What Are the Complications in Newborns?

• Newborn infants presenting with HFM have not only common airway and feeding difficulties due to an underdeveloped pharynx, larynx, esophagus, etc. However, the complications further that they cannot breastfeed easily, perform functions from the lower jaw or mandible, or exercise the mastication muscles.

• Further complications that are encountered with HFM disease are obstructive sleep apnea, swallowing difficulties, etc.

• In infants that are born with cleft lip and palate, up to 17.6 percent, 13.5 percent, and 15.9 percent of patients also have craniofacial malformations as in HFM.

What Are the Different Reconstructive Surgeries Based on Hfm?

Reconstructive surgery is the most recommended treatment choice for HFM infants, with the main long-term goal of improving individual facial symmetry and jaw function and restoring normal occlusion in early childhood.

• Grafts: These are the recommended choices for facial reconstruction surgeries. The grafts can be harvested from several sites in the body, like the costochondral cartilage, iliac crest, temporal bone, or fibula, to augment the hypoplastic features of the lower jaw or mandible. With the current advent of mandible distraction, grafts are used as a supplement for reconstructing these deformities that mainly involve the child's temporomandibular joint and the lower jaw or mandibular ramus.

• Mandibular Distraction Osteogenesis (MDO): It is a more popular reconstructive procedure used by maxillofacial surgeons that aims to expand the lower jaw or mandible through the lengthening of the mandibular bone. Instead of relying on graft placement, MDO relies on new bone growth formation as a natural result of this technique (instead of on the donor graft material)

• Soft Tissue Correction Procedures: These are the commonly performed facial procedures in children soon after the realignment surgery of the facial skeleton. Several options exist for modern-day oral and maxillofacial surgeons to augment HFM children. These include microvascular free tissue transfer, autologous grafting of fat, etc, or even using high-density porous polyethylene implants.

• Ear Reconstruction: It can further be an integral part of facial reconstruction in HFM. In children with deformities involving the auricle, external auditory canal, or middle ear structures, this necessitates the need for immediate reconstruction with long-term goals to improve their hearing functions.

Conclusion

Hemifacial microsomia is a congenital and complex craniofacial condition presenting in the newborn that presents multiple challenges to the surgeon. The long-term management of goals for maxillofacial surgeons includes restoring esthetic and functional efficiency for the child by eliminating all jaw-based, midface, and craniofacial disturbances.