Congenital jaw anomalies include a jaw that is missing, deformed, or incompletely developed, often in conjunction with other congenital anomalies and syndromes.
A clinical geneticist can help guide the evaluation even in cases of apparent isolated congenital anomaly. Identification of the underlying syndrome is important for prognosis and family counseling. (See also Overview of Congenital Craniofacial Anomalies.)
Chromosomal microarray analysis, specific gene tests, or broader gene panel tests should be considered in the evaluation of patients with congenital craniofacial anomalies. If the results of these tests are nondiagnostic, clinical exome sequencing analysis or clinical genome sequencing may be recommended.
Micrognathia (Small Mandible)
Congenital micrognathia occurs in approximately 1 in 20,000 births and may occur in hundreds of genetic syndromes (1).
Micrognathia is a common manifestation of Pierre Robin sequence and is characterized by a U-shaped cleft of the soft palate and upper airway obstruction caused by glossoptosis (a tongue that falls to the back of the throat). Airway management can be challenging both because of the small jaw structures and oropharynx, because the tongue is positioned posteriorly and may obstruct the pharynx. Feeding can be difficult. Prone positioning during feeding may help, but uncoordinated swallowing may require nasogastric gavage feedings or a gastrostomy tube. If cyanosis or respiratory problems persist, tracheostomy or surgery to affix the tongue in a forward position (eg, suturing it to the inner lower lip) may be required. Conductive hearing loss may also be present, so otologic evaluation is indicated.
More than half of patients with micrognathia, in some studies, have associated anomalies that suggest an underlying chromosomal defect or genetic syndrome (2–4). Some of the diagnoses to be considered include Treacher Collins syndrome (associated with downward slant of the eyes, coloboma of the eyelid, malformed pinna [microtia], and hearing loss), Nager syndrome, Goldenhar (oculoauriculovertebral) syndrome, and cerebrocostomandibular syndrome. Radiographs or CT is often performed to help further define the anatomy.
Surgical extension of the mandible can improve appearance and function. In the typical procedure, called distraction osteogenesis, an osteotomy is performed and a distraction (separator) device is attached to both pieces. Over time, the distance between the 2 pieces is widened, and new bone grows in between to enlarge the mandible.
Micrognathia (small mandible) reference
1. Chen Q, Zhao Y, Qian Y, Lu C, Shen G, Dai J. A genetic-phenotypic classification for syndromic micrognathia. J Hum Genet. 2019;64(9):875-883. doi:10.1038/s10038-019-0630-4
2. Mouthon L, Busa T, Bretelle F, et al. Prenatal diagnosis of micrognathia in 41 fetuses: Retrospective analysis of outcome and genetic etiologies. Am J Med Genet A. 2019;179(12):2365-2373. doi:10.1002/ajmg.a.61359
3. Nicolaides KH, Salvesen DR, Snijders RJ, Gosden CM. Fetal facial defects: associated malformations and chromosomal abnormalities. Fetal Diagn Ther. 1993;8(1):1-9. doi:10.1159/000263740
4. Breugem CC, Evans KN, Poets CF, et al. Best Practices for the Diagnosis and Evaluation of Infants With Robin Sequence: A Clinical Consensus Report. JAMA Pediatr. 2016;170(9):894-902. doi:10.1001/jamapediatrics.2016.0796
Agnathia
Congenital absence of the condyloid process (and sometimes the coronoid process, the ramus, and parts of the mandibular body) is a severe malformation. The mandible deviates to the affected side, resulting in severe malocclusion; the unaffected side is elongated and flattened. Anomalies of the external, middle, and inner ears, temporal bone, parotid gland, masticatory muscles, and facial nerve often coexist (1). Syndromes to be considered include agnathia-holoprosencephaly, otocephaly, a severe form of cerebrocostomandibular syndrome, and Ivemark syndrome.
Radiographs or facial CT of the mandible and temporomandibular joint shows the degree of underdevelopment and distinguish agenesis from other conditions that result in similar facial deformities but do not involve severe structural loss. Facial CT is usually performed before surgery.
Treatment of agnathia consists of prompt reconstruction with autogenous bone grafting (costochondral graft) to limit progression of facial deformity. Often, mentoplasty, onlay grafts of bone and cartilage, and soft-tissue flaps and grafts further improve facial symmetry. Distraction osteogenesis, in which an osteotomy is performed and a distraction (separator) device is attached to both pieces of the mandible, is being increasingly used. Orthodontic treatment in early adolescence helps correct malocclusion.
Agnathia reference
1. Dubucs C, Chassaing N, Sergi C, et al. Re-focusing on Agnathia-Otocephaly complex. Clin Oral Investig. 2021;25(3):1353-1362. doi:10.1007/s00784-020-03443-w
Maxillary Hypoplasia
Maxillary hypoplasia is underdevelopment of the maxillary bones that causes midfacial retrusion and creates the illusion of protuberance (jutting forward) of the lower jaw.
Radiographs or facial CT shows the degree of underdevelopment.
Treatment of maxillary hypoplasia may involve surgery or orthodontic headgear, depending on the severity.
This photo shows a patient with maxillary hypoplasia (small upper mandible) in addition to ocular hypertelorism. She also has other facial deformities including flat nasal bridge, upslanting palpebral fissures, epicanthal folds, low-set ears, and retrognathism.
