Continuing Education Activity

Hemifacial microsomia (HFM) is a congenital craniofacial anomaly characterized by asymmetric underdevelopment of facial structures derived from the first and second pharyngeal arches, including the mandible, maxilla, external ear, and orbital region. As the second most common craniofacial condition after cleft lip and palate, HFM presents along a broad clinical spectrum, ranging from mild mandibular hypoplasia to extensive craniofacial deformities. The etiology is believed to involve vascular disruption during embryogenesis, particularly affecting the stapedial artery; however, environmental and maternal risk factors, such as diabetes and teratogenic exposures, are also implicated. Diagnostic evaluation relies on clinical examination and advanced imaging modalities, including 3-dimensional computed tomography and magnetic resonance imaging, to assess bone and soft tissue involvement. Management is tailored to the individual's severity and developmental potential and frequently involves staged surgical correction, emphasizing the importance of early recognition and longitudinal care.

Through this educational activity, participants enhance their ability to identify the clinical features and underlying mechanisms of HFM and apply appropriate diagnostic and therapeutic strategies. The course emphasizes the integration of knowledge regarding embryologic development, radiologic interpretation, and surgical planning. Clinicians gain practical tools for assessing disease severity and planning individualized interventions across the patient's developmental trajectory. Engagement with an interprofessional team—including surgeons, radiologists, audiologists, orthodontists, and speech-language pathologists—ensures a comprehensive and coordinated approach to care. This collaborative framework supports improved functional, aesthetic, and psychosocial outcomes for patients affected by HFM.

Objectives:

• Identify the clinical and diagnostic features indicative of hemifacial microsomia.
• Apply current understanding of embryologic development and pathophysiology to guide clinical decision-making.
• Improve strategies for counseling patients and parents to foster informed consent and collaborative decision-making in hemifacial microsomia management.
• Collaborate with all members of the interprofessional team, including specialists such as otolaryngologists, ophthalmologists, geneticists, plastic surgeons, and nurses, to provide efficient, comprehensive, and coordinated care for individuals with hemifacial microsomia.

Introduction

Hemifacial microsomia, also known as unilateral otomandibular dysostosis or lateral facial dysplasia, is a congenital malformation characterized by asymmetry of the first and second branchial arches. This condition is the 2nd most common craniofacial anomaly after cleft lip and palate.[1] The terms "hemifacial microsomia" and "craniofacial microsomia" are often used interchangeably. However, craniofacial microsomia refers more broadly to any asymmetrical development of the craniofacial skeleton, including ipsilateral skull base hypoplasia. In contrast, hemifacial microsomia most commonly describes maxillary-mandibular hypoplasia involving the pharyngeal arch structures described. For consistency, this activity will use the term hemifacial microsomia (HFM) throughout.[2]

Patients typically present with unilateral hypoplasia of the ear, facial skeleton (including the maxilla, mandible, zygoma, and temporal bones), and surrounding soft tissue, although bilateral cases have been reported (see Image. Bilateral Hemifacial Microsomia).[3][4][5] HFM and Goldenhar syndrome, also known as Goldenhar-Gorlin syndrome, are considered variants within the same clinical continuum of disorders, termed the oculoauriculovertebral spectrum. Goldenhar syndrome includes HFM phenotypes along with epibulbar dermoid and vertebral anomalies.[6]

Etiology

HFM results from dysfunction of the first and second branchial arches, which derive from neural crest cells (NCCs).[7] The cause remains uncertain, with leading theories including vascular injury to the stapedial artery, anomalous migration of NCCs, and disruption of Meckel cartilage formation.[8][9] The heterogeneous phenotypic presentation likely arises from a combination of genetic and environmental factors that disrupt vascularization and development of the first 2 pharyngeal arches during the first 4 weeks of embryonic development.[10]

During embryogenesis, the first branchial arch gives rise to the maxilla, mandible, zygoma, muscles of mastication, trigeminal nerve, anterior auricle (tragus, helical root, helix), malleus, and incus. The second branchial arch forms the hyoid bone, muscles of facial expression, facial nerve, stapes, and the remainder of the auricle (antihelix, antitragus, and lobule). Genetic defects, teratogens, smoking, hormonal therapy, vascular injury, vasoactive medications, cocaine, and maternal-fetal conditions such as diabetes, hypothyroidism, and celiac disease can disrupt development, causing hypoplasia or aplasia.[11][12][13] Genetic mutations and chromosomal abnormalities associated with HFM include trisomy 10p, 12p13.33 microdeletion, 22q11.2 microdeletion, large 5p deletion, and a 10.7 cM region on chromosome 14q32.[14]

Epidemiology

HFM ranks as the second most common congenital craniofacial defect after cleft lip and palate. Most cases occur sporadically, though both autosomal dominant and recessive inheritance patterns with incomplete penetrance have been reported.[15][16] The incidence in the United States ranges from 1 in 3500 to 1 in 5600 live births.[17] Some studies describe a 3:2 male predominance, with most patients exhibiting right-sided defects, while others report no significant differences in sex or laterality.[18][19][20] Bilateral presentation occurs in up to 10% of cases, most frequently associated with autosomal dominant inheritance.[21]

Pathophysiology

HFM develops through 3 interrelated pathogenic models, none of which fully explains its varied presentations. Different phenotypes may result from distinct factors influencing each model. The vascular abnormality and hemorrhage model, first proposed by Poswillo in 1973, suggests that embryonic hemorrhage around the stapedial artery causes hematoma formation and ischemia, leading to underdevelopment of adjacent structures. The stapedial artery, which initially supplies the first and second branchial arches before being replaced by the external carotid artery system, may be affected by agents such as thalidomide and vasoconstrictive medications, including epinephrine.[22][23] Impaired vascular endothelial growth factor further compromises the blood supply to the Meckel cartilage, leading to mandibular hypoplasia.[24] This model explains the typical unilateral and nonspecific pattern of HFM, with varying soft tissue damage depending on tissue proximity to the hemorrhage and degree of vascular injury.

The second model focuses on interference with Meckel cartilage development. The structure originates from the first branchial arch and forms the malleus, incus, and mandible. Teratogens, hemorrhage, or genetic defects disrupting this process lead to unilateral malformed ossicles and mandibular hypoplasia.[25] This theory complements the vascular model, as both contribute to mandibular underdevelopment. Abnormal migration, proliferation, and differentiation of NCCs represent another pathogenic model for HFM. Genetic defects, teratogens, and environmental factors can directly damage NCCs. The OTX2 gene, crucial for NCC development, shows that its deletion causes mandibular dysostosis. Elevated embryonic glucose from maternal diabetes reduces NCC tolerance to oxidative stress, leading to apoptosis and resulting in facial and cardiac anomalies.[26]

HFM presents with a wide spectrum of deformities involving the eyes, ears, and the first 2 pharyngeal arches. Ocular abnormalities include strabismus, anophthalmia, microphthalmia, eye asymmetry, cleft eyelid, and exophthalmia. Auricular anomalies consist of preauricular appendage, preauricular fistula, microtia, ear asymmetry, and external auditory canal atresia. Deformities of the first and second pharyngeal arches include cleft lip and palate, bifid tongue, mandibular hypoplasia, maxillary hypoplasia, oral malocclusion, and dental malformations. Although HFM implies facial involvement only, extracranial defects frequently occur.[27] Neurological abnormalities affect 5% to 15% of patients, cardiac defects range from 14% to 47%, genitourinary anomalies appear in 5% to 6%, pulmonary and gastrointestinal malformations occur in 10%, and skeletal malformations affect 40% to 60%.[28][29][30]

History and Physical

Children with HFM require a thorough, 3-generation family history to detect malformations typical of the condition. A detailed prenatal and birth history should capture maternal-fetal factors like gestational diabetes, maternal hypothyroidism, and exposure to medications or substances during pregnancy. Parents should be questioned about obstructive sleep symptoms, feeding and swallowing difficulties, and speech development.

The physical examination should emphasize identifying facial deformities and asymmetries involving the auricle, ossicles, zygoma, maxilla, mandible, jaw function, and dental occlusion. Careful bimanual palpation of the affected facial bones is necessary to distinguish hypoplasia from aplasia. Ophthalmologic signs such as ocular dermoid cysts and vertebral anomalies like scoliosis may suggest the more severe Goldenhar syndrome variant.

Evaluation

The minimal diagnostic criteria for HFM require either of the following:

• Ipsilateral defects of the mandible and auricle
• Asymmetric defects of the mandible or auricle combined with 2 or more indirectly associated anomalies
• A positive family history of HFM [31]

The posteroanterior cephalogram remains the gold standard for evaluating facial asymmetry. Measurements of midline deviation of the maxilla and mandible, ramus height, and occlusal cant guide surgical planning. Photography documents facial appearance throughout treatment. Additional imaging, such as computerized tomography (CT), assists in assessing ossicles, the middle ear cavity, and facial bone morphology for preoperative evaluation.[32] Three-dimensional facial skeleton models derived from CT scans facilitate the accurate placement of surgical devices.[33]

Many patients with HFM experience airway and feeding challenges due to underdevelopment of the pharynx, larynx, esophagus, mandible, and masticatory muscles.[34] Obstructive sleep apnea, swallowing difficulties, and cleft lip and palate occur in 17.6%, 13.5%, and 15.9% of patients with craniofacial malformations, respectively.[35][36][37] Patients with micrognathia and symptoms of OSA should undergo polysomnography and swallowing evaluation by a speech-language pathologist.

Additional assessments include audiograms to evaluate hearing loss, perceptual speech analysis to assess speech development, and psychosocial evaluations. Cervical spine radiographs screen for vertebral anomalies, while renal ultrasound detects noncraniofacial malformations. Chromosomal analysis and genetic counseling may be offered to families with suspected hereditary cases.

Treatment / Management

Given the heterogeneous presentation of HFM, an individualized, interprofessional approach is essential. Functional impairments such as airway obstruction and dysphagia require immediate attention. Patients often exhibit a narrow oropharyngeal airway and nasal obstruction caused by midface and mandibular hypoplasia, leading to complications such as difficult intubation, obstructive sleep apnea, and respiratory distress.[38] Tracheotomy remains the standard treatment for severe airway obstruction.[39][40] Neonatal distraction osteogenesis has been described but is less effective in craniofacial malformations than in the Pierre Robin sequence due to a lack of catch-up growth. Infants with dysphagia may require gastrostomy tubes to maintain nutrition. Reconstructive surgery aims to improve facial symmetry, jaw function, and achieve normal occlusion. The severity of the defect typically guides the type of surgery.

Grafts

Gillies first described grafts in the 1920s. Cartilage and bone may be harvested from costochondral cartilage or the iliac crest, calvarium, or fibula to augment the hypoplastic mandible. Disadvantages of grafting include wound infection, donor site defects, reankylosis of the temporomandibular joint (TMJ), possible fractures, graft material resorption, and recurrence of asymmetry.[41] With the introduction of mandibular distraction, grafts now serve as a supplement in reconstructing deformities involving the TMJ and ramus.[42]

Mandibular Distraction Osteogenesis

McCarthy popularized mandibular distraction osteogenesis (MDO) in the 1990s.[43] The procedure expands the mandible by lengthening the bone itself. Bilateral mandibular osteotomies create segments gradually drawn apart to stimulate new bone growth between them. Unlike graft placement, MDO depends on the formation of new bone rather than donor material. Advantages of MDO over grafts include lower recurrence of asymmetry, less blood loss, shorter operative time, improved soft tissue symmetry, absence of donor site morbidity, and suitability for younger patients.[44][45][46]

External distractors were used originally, which may be removed easily by unscrewing pins without additional surgery. However, external devices caused patient discomfort, were vulnerable to trauma, and led to social embarrassment due to their visibility. Complications such as visible scars, hardware infections, and dislodgement prompted the development of internal mandibular distractors with superior mechanical strength. Internal devices offer greater stability, showing a relapse rate of 13.33% compared to 23.52% for external distractors.[47]

Drawbacks of internal devices include the need for a second operation to remove hardware, scarring, device malfunction, inappropriate distraction, injury to the teeth, TMJ, or nerves, infection, and bony overgrowth over the device.[48][49] Compared to internal distractors, external devices allow longer distraction lengths and greater flexibility in positioning, especially for children with short mandibles and limited subperiosteal space for internal device placement. Surgeons must be prepared to use either technique and tailor treatment to each patient’s anatomy. Severe occlusal cant may necessitate more extensive procedures such as 2-jaw orthognathic surgery during adolescence or early adulthood.[50]

Soft Tissue Correction

Soft tissue correction follows facial skeletal realignment. Methods to augment surrounding tissue include microvascular free tissue transfer, autologous fat grafting, and implants such as high-density porous polyethylene.[51][52] Autologous fat grafting requires more operative procedures and permits lower volume transfer, which can contribute to greater asymmetry compared to free tissue transfer. Advantages of fat grafting include fewer complications, shorter total operative time, and comparable patient and surgeon satisfaction.[53]

Ear Reconstruction

HFM can involve deformities of the auricle, external auditory canal, and middle ear structures. Presentations range from mild hypoplasia, requiring ear cartilage reshaping, to complete anotia with middle ear involvement, necessitating total auricular reconstruction. Reconstruction options include autologous costal cartilage grafts and synthetic implants, each with distinct advantages and disadvantages. Learners seeking a detailed discussion of microtia reconstruction are referred to specialized literature for further information.

A less invasive alternative involves the placement of a prosthetic ear, which may be adhered with adhesives or attached to an osseointegrated anchor surgically implanted. Prostheses offer upgrade options as patients grow and avoid donor site morbidity. A notable limitation of osseointegrated anchors is that placement precludes the use of other reconstruction methods.

Differential Diagnosis

HFM can present with a heterogeneous array of facial defects of varying severity. Many disorders involving facial anomalies may be mistaken for HFM, including the following:

• CHARGE (coloboma, heart defects, atresia choanae, growth retardation, genital abnormalities, and ear anomalies) 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
• Branchiootorenal syndrome
• Maxillofacial dysostosis

Accurate diagnosis requires careful evaluation to distinguish HFM from these other syndromes and conditions. Interprofessional assessment improves management and outcomes for affected individuals.

Treatment Planning

The timing of reconstructive surgical intervention remains a matter of controversy. Proponents of early intervention hypothesize that mandibular asymmetry worsens over time due to minimal growth on the affected side, resulting in secondary deformities. Early surgery may improve growth potential, masticatory function, dental development, and patient self-confidence.[54] Supporters of delayed intervention recommend correction after skeletal and dental maturity—around age 15 in boys and 13 to 15 in girls—to reduce the risk of relapse, minimize additional surgeries, decrease blood loss, and enhance patient compliance. Large systematic reviews found no evidence supporting early surgical reconstruction and advise postponing surgery until dental and bone growth is complete.[55]

Treatment timing depends on the patient’s age and the severity of malformations. During infancy, indicated interventions include correction of cleft lip and palate, hearing aids for hearing loss, osteotomies for significant orbital dystopia, and mandibular distraction for severe retrognathia causing respiratory or feeding difficulties. Tracheostomy may be necessary in severe cases. Reconstruction of the malformed auricle or prosthesis placement is recommended during skeletal growth between the ages of 6 and 12.[56]

Maxillary and mandibular defects may be managed with orthodontic devices in milder cases or as adjuncts to surgical repair in most patients.[57] Costochondral grafts and mandibular distraction osteogenesis remain options when appropriate. In adolescence and adulthood, definitive facial skeleton reconstruction aims to improve facial symmetry and occlusion. Soft tissue augmentation, using either free tissue transfer or fat grafting, is performed as needed. Revision surgeries are also typically scheduled during this period.

Staging

Due to the highly variable presentation of HFM, several classification systems have been developed to better characterize phenotypic differences, aiding diagnosis, treatment planning, and prognosis. The earliest classification by Pruzansky in 1969 focused on mandibular and glenoid fossa characteristics. Later, David et al introduced the SAT (skeletal malformations, auricular involvement, and soft tissue defects) system in 1987, which was expanded by Vento et al into the OMENS (Orbit, Mandible, Ear, Nerve, Soft tissue) classification.[58] Finally, Tuin et al developed OMENS plus to include abnormalities beyond craniofacial structures.[59]

Pruzansky Classification

This system categorizes mandibular hypoplasia into 3 groups based on radiological features, later modified by Kaban et al to incorporate TMJ status.

• Grade 1: Mandible smaller than the unaffected side
• Grade 2a: Shortened ramus with a normal glenoid fossa
• Grade 2b: Shortened ramus with malpositioned glenoid fossa requiring TMJ reconstruction
• Grade 3: Severe distortion or absence (agenesis) of the ramus [60]

Skeletal Malformations, Auricular Involvement, and Soft Tissue Defects System

The SAT system is modeled after the cancer tumor, node, metastasis (TNM) staging system. Alphanumeric grades are assigned to skeletal malformations (S). S1 to S3 correspond to Pruzansky’s grades for skeletal involvement. S4 and S5 indicate orbital involvement.

Auricular (A) scores in the SAT classification include the following:

• A0: Normal auricle
• A1: Malformed auricle with mostly normal features
• A2: Retains some normal structures but with deficient upper ear cartilage
• A3: Severely malformed auricle with abnormal lobule and largely absent pinna, based on Meurman et al’s microtia staging [61]

Soft tissue (T) scores range from T1, corresponding to minimal deformity, to T3, presenting with severe facial defects affecting cranial nerves, parotid gland, masticatory muscles, or cleft lip, as described by Murry et al.[62]

Orbit, Mandible, Ear, Nerve, Soft Tissue Classification

The OMENS system provides a more comprehensive assessment, grading 5 anatomical categories: orbit, mandible, ear, nerve, and soft tissue. Each category is scored from 0 (normal) to 3 (most severe). The OMENS plus system further incorporates extracranial abnormalities. This classification is considered flexible and sensitive, effectively capturing the broad phenotypic spectrum of HFM.

Prognosis

MDO effectively lengthens the mandible and improves facial symmetry, appearance, and dental occlusion, as demonstrated by postoperative cephalograms and radiographs.[63] However, long-term outcome data remain limited. Follow-up studies reveal a high recurrence rate. Hollier et al reported recurrence rates between 51% and 100% occurring 42 to 92 months after surgery. Similar recurrence rates requiring revision surgery have been documented in other studies.[64][65] These findings underscore the importance of ongoing monitoring until skeletal and dental maturity is achieved. In 2012, Mezzini et al found that genetic factors influence the asymmetrical facial growth patterns in HFM patients, which tend to revert to their original asymmetry even after distraction osteogenesis.[66] Counseling patients and families about the significant likelihood of revision surgeries throughout childhood and adolescence remains essential.[67]

Complications

MDO is the preferred method of treatment for patients with HFM, but it can present with challenges and complications. A systematic review by Verlinden et al found a complication rate of 43.9%, with 13.9% requiring revision surgery, hospitalization, or resulting in permanent sequelae.[68] Nerve injury to the inferior alveolar nerve or mental nerve ranged from 4.2% to 37.5%.[69][70]

Mucosal and soft tissue dehiscence occurred in 1.6% to 3.1% of cases due to the thin soft tissue overlying the hypoplastic bone. Lingual displacement from traction by the mylohyoid muscle on the osteotomized segment was reported in 7.6% of cases.[71][72] Mandibular misalignment occurred in 0.6% of cases.[73] Mandible fracture was seen in 2.8%.[74] Other complications include bony nonunion, insufficient bone formation, hardware exposure, facial scarring, wound infection, and mandibular necrosis.

Postoperative and Rehabilitation Care

Patients are admitted for airway observation after surgical placement of internal distractors. Discharge occurs once patients breathe without difficulty and tolerate an adequate diet. Following a latency period of 4 to 7 days in school-aged children, distraction begins at a rate of 1 to 2 mm per day. This gradual bone lengthening continues until the desired length, based on preoperative planning, is achieved. Parents receive training on how to adjust the distractor and maintain surgical site hygiene at home. Upon completion of distraction, the externally exposed rods are removed near the skin. After 2 to 3 months of bone consolidation in school-aged children, patients return to the operating room for removal of the internal device. A series of cephalograms is obtained at the start of activation, end of activation, before device removal, and 1 year postoperatively.[75][76]

Consultations

HFM may result from aberrant neurological regeneration affecting the salivary glands and integumentary system. Diagnosis and management require an interprofessional team comprising an otolaryngologist, plastic reconstructive surgeon, oral and maxillofacial surgeon, ophthalmologist, primary care clinician, psychologist, geneticist, and nursing staff.

Deterrence and Patient Education

Educating patients and families about HFM presents challenges due to the condition’s heterogeneous presentation and the need for coordinated interprofessional care. Early involvement of an SLP is essential to address functional deficits in speech and swallowing. Referral to a genetic counselor helps identify and discuss potential genetic and chromosomal abnormalities within the family.

Patients and families should understand the various treatment options and the timeline for reconstructive surgery. Study results indicate that recurrence of asymmetrical bony growth frequently occurs after primary surgical management. Delaying surgery until skeletal and dental maturity often reduces the need for revision procedures.[77] However, prolonged visible and functional impairments can significantly affect psychosocial development and personality formation in children. Counseling should cover the advantages and disadvantages of earlier surgical intervention, which may provide a more typical childhood experience but carries a higher likelihood of revision surgery. Conversely, delayed surgery may minimize the need for revisions but prolong functional and cosmetic impairments during critical developmental years.

Enhancing Healthcare Team Outcomes

Patients with HFM require coordinated care from an interprofessional team, including otolaryngologists, plastic surgeons, oral and maxillofacial surgeons, ophthalmologists, audiologists, speech-language pathologists (SLPs), primary care clinicians, psychologists, and geneticists. Children born with hypoplastic facial defects should undergo thorough evaluation by primary clinicians and geneticists for prompt diagnosis and timely referral to reconstructive surgeons. Other craniofacial microsomia syndromes presenting with similar features should be considered to identify any associated vertebral or internal organ malformations, ensuring comprehensive assessment and tailored management.

Study results indicate reconstruction is optimally performed after children reach skeletal and dental maturity. Since patients with HFM often require multiple surgeries throughout childhood and adolescence, close follow-up with primary clinicians and reconstructive surgeons is essential to monitor both immediate and long-term functional and aesthetic outcomes. Patients may experience social and functional impairments related to their condition. Referral to SLPs for speech and swallowing therapy is recommended alongside psychosocial support. Participation in formal peer support groups with others affected by similar craniofacial malformations can help patients and families address emotional and social concerns.

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Disclosure: Allen Young declares no relevant financial relationships with ineligible companies.

Disclosure: Ryan Winters declares no relevant financial relationships with ineligible companies.

Disclosure: Alycia Spinner declares no relevant financial relationships with ineligible companies.