4 Craniofacial Microsomia



10.1055/b-0038-162656

4 Craniofacial Microsomia

Patrick A. Gerety, Albert K. Oh, and Jesse A. Taylor


Summary


Management of Mandibular Hypoplasia in Pediatric Unilateral Craniofacial Microsomia attempts to succinctly describe the major principles of the surgical treatment of mandibular asymmetry in patients with unilateral craniofacial or hemifacial microsomia. This chapter also delves into some of the important controversies regarding the surgical management of mandibular hypoplasia, particularly in regards to long-term results.




4.1 Introduction


Hemifacial or craniofacial microsomia (CFM) represents a wide group of malformations primarily involving structures derived from the first and second branchial arches. With reported incidences ranging from 1 in 3,000 to 1 in 20,000, this heterogeneous disorder of craniofacial morphogenesis represents the second most common craniofacial anomaly after cleft lip/palate. Although the etiology of CFM is unclear, two major theories include vascular disruption of the stapedial artery that supplies the first and second pharyngeal arches and abnormal migration of key neural crest cells during embryogenesis. The latter theory provides a more plausible explanation for the bilateral craniofacial features and extracraniofacial findings often seen in expanded-spectrum CFM.



4.2 Diagnosis


With the ongoing advancements in ultrasonography and prenatal magnetic resonance imaging (MRI), CFM can be diagnosed prenatally. However, it is much more common for clinical suspicion to arise postnatally. Abnormalities of the external ear, facial asymmetry, and facial paralysis are most likely to be identified by neonatologists and pediatricians.



4.2.1 Classification System


Although several systems exist for classifying CFM, the OMENS-Plus classification is the most frequently utilized. The OMENS-Plus classification (Fig. 4‑1) succinctly describes and grades the five major craniofacial abnormalities of CFM, specifically involving the (1) orbit, (2) mandible, (3) ear, (4) nerve (facial), and (5) soft tissue deficit. Scores range from 0 (normal) to 3 (most severe). The plus designation applies to extracraniofacial anomalies, with the most common associated abnormalities involving the central nervous, skeletal, and cardiac systems. Patients with more severe CFM (i.e., those with higher OMENS score) have significantly greater risk of having noncraniofacial anomalies, lending further support to the theory of neural crest involvement in the etiopathogenesis of CFM. The clinical features and their severity will be discussed as follows in the order of the OMENS-Plus classification system.

Fig. 4.1 OMENS classification. The severity of the clinical features of craniofacial microsomia is described in this classification. The specifics of each category can be found in their respective text in this chapter.



4.2.2 Orbit


The orbit is affected in a minority (20–30%) of patients with CFM. Orbital manifestations of CFM include a reduction in the dimensions (O1), inferior positioning resulting in vertical orbital dystopia (O2), and, in severe cases, a severely constricted orbit (O3) featuring microphthalmia and hypoplastic lids. Patients with microphthalmia often do not have vision in the affected eye (Fig. 4‑2).

Fig. 4.2 Orbital deformity in craniofacial microsomia—microphthalmia. This figure demonstrates the severity of the deformity that may occur in the orbit. This patient had been previously treated for craniosynostosis.



4.2.3 Mandible


Mandibular hypoplasia is the hallmark of CFM and affects 90 to 100% of patients. The mandibular component of CFM has received the most attention in the literature. This is related to surgical innovations (distraction osteogenesis [DO]) and the degree of facial normalization that mandibular surgery can produce. The morphology of the CFM mandible is quite variable (Fig. 4‑3), and there has been a vigorous debate about the best way to classify the patients. Although there are several classification schemes, the Kaban-modified Pruzansky’s system is the most commonly used: type I is a small mandible with normal morphology; type IIa is a mandible with a ramus that is abnormal in size and shape but with a normal temporomandibular joint (TMJ); and type IIb is a mandible with an abnormal ramus and TMJ. Type III deformity is defined by an absent ramus, condyle, and TMJ.

Fig. 4.3 Spectrum of mandibular deformities in craniofacial microsomia on CT scan. (a) CT demonstrates a smaller right mandibular ramus with an occlusal cant. The effect on the mandible is relatively mild. (b) CT demonstrates highly abnormal left hemimandible with absent ramus, condyle, and coronoid.


In general, the CFM mandible is smaller than the contralateral normal mandible. Much of this size difference is seen in the condyle–ramus portion of the mandible. In mild cases, the effect on the ramus is largely vertical shortening, resulting in decreased posterior facial height and occlusal canting upward on the affected side. In severe cases, specific portions of the mandible, including the condyle, the ramus, the glenoid fossa, and the TMJ, may be absent or unrecognizably distorted. An important observation is that the affected condyle and ramus are shifted medially, contributing to decrease in transverse facial width.


Because moderately and severely affected mandibles are so morphologically affected, classification systems have been found to be unreliable, even among expert raters. Hypoplasia of the maxilla was long thought to be a part of CFM, but vigorous examination has not shown this to be true. The maxilla appears to be normal in volume but malpositioned secondary to the abnormal CFM mandible.



4.2.4 Ear


As with all other manifestations of CFM, ear anomalies range from mild hypoplasia to complete anotia. From the OMENS classification, E1 represents mild hypoplasia, often with cupping of the affected ear; E2 represents absent auditory canal and hypoplastic abnormal appearing ear remnant, and E3 represents severe microtia with all but a small remnant missing (e.g., lobular type). Preauricular remnants are also commonly found anterior to the tragus. Studies demonstrate that the ear is affected in 80 to 90% of patients, with as many as 50% of patients having microtia (E3). Hearing impairment is common on the affected side in CFM, occurring in approximately 75% of patients. Nearly all of those patients have conductive hearing loss; however, about 10% of all patients with CFM have sensorineural hearing loss as well.



4.2.5 Nerves


Anomalies of the nervous system, including aberrant brain anatomy, may been seen in CFM. However, the most common finding is partial facial nerve (CN VII) palsy. Facial nerve involvement is found in approximately 40% of patients with CFM. This palsy is more likely to affect the lower face (buccal, marginal mandibular, and cervical branches) than the upper face (zygomatic and frontal branches). A small percentage of patients with CFM have complete facial palsy. The OMENS classification describes facial palsy as either upper (N1), lower (N2), or total (N3).


Clinical manifestations of facial paralysis include inability to close the eyelid, lack of animation of the forehead, lack of active/symmetric smile, drooling, and asymmetry of lip depressors.



4.2.6 Soft Tissue


All layers of the soft tissue on the affected side of a patient with CFM may be deficient. This includes skin, subcutaneous fat, and muscles of animation and mastication. In moderate and severe cases, this deficiency immediately draws the attention of an observer to the asymmetry of the face. The most notable areas of deficiency are in the temporal fossa, in the malar/zygomatic region, and along the lower mandibular border. The severely affected CFM mandible contributes to the appearance of soft tissue deficiency, because the condyle and ramus are shifted medially, robbing the face of transverse width. The OMENS classification describes this soft deficiency as mild (S1), moderate (S2), or severe (S3). Macrostomia, or clefting at the oral commissure, also known as a Tessier 7 cleft, occurs in approximately 25% of patients with CFM. The orbicularis oris is discontinuous and can contribute to poor oral competence and abnormal appearance in both repose and animation.



4.2.7 Noncraniofacial Manifestations


Noncraniofacial anomalies were long thought to identify a patient with “syndromic CFM,” usually Goldenhar’s syndrome. The current understanding is that the error in neural crest cell migration responsible for facial manifestation of CFM is also the cause of noncraniofacial problems. The most common extracraniofacial anomalies occur in the heart (25% of patients with CFM), kidneys (10% of patients with CFM), skeleton (40% of patients with CFM), and central nervous system (CNS). Common cardiac defects include atrial and ventricular septal defects. Skeletal anomalies are most often scoliosis and overt vertebral abnormalities. The most common CNS problem is hydrocephalus. One of the pathognomonic findings is epibulbar dermoids of the eyelid.



4.2.8 Differential Diagnosis


A number of different diagnoses produce facial asymmetry that could resemble CFM to the untrained eye. Often, these other diagnoses can be excluded based on their timing of onset and specific phenotype. Examples of these diagnoses include Parry–Romberg disease, TMJ ankylosis, and radiation-induced tissue atrophy. Severe Tessier 7 can mimic CFM as well.


Facial asymmetry may be caused by hypoplasia or hyperplasia. Hemifacial hypertrophy and an infiltrating lipomatosis are rare conditions that create facial asymmetry. Condylar hypoplasia and hyperplasia should also be considered.


Treacher Collins syndrome (TCS) may be confused for bilateral CFM. Treacher Collins syndrome is a heritable (autosomal dominant) syndrome characterized by panfacial bone hypoplasia, bilateral Tessier clefts, and severe antimongoloid palpebral slant, culminating in a very characteristic phenotype.


One recently identified diagnosis, condylar–coronoid collapse, is believed to mimic CFM in producing mandibular conformation similar to mild to moderate CFM. It is noted to have a deep sigmoid notch, but the patients demonstrate no other OMENS-related features of CFM.



4.2.9 Natural History


The natural history of CFM is poorly understood. One fundamental question is whether the CFM deformity will worsen as a child ages. Furthermore, will interventions such as mandibular reconstruction mitigate or exacerbate age-related change? This has been studied most intensively pertaining to the mandible, which can be measured radiographically. Through a number of different methods, the affected mandible has been shown to grow but at a rate less than the rate of growth of the unaffected side. Given this, the phenotype of a growing patient is likely to worsen slightly as he or she grows (i.e., occlusal cant and facial soft tissue asymmetry).

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May 18, 2020 | Posted by in Pediatric plastic surgery | Comments Off on 4 Craniofacial Microsomia
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