Congenital jaw anomalies include a jaw that is missing, deformed, or incompletely developed, often in conjunction with other congenital anomalies and syndromes.
(See also Overview of Congenital Craniofacial Anomalies.)
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.
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, whole exome sequencing analysis may be recommended.
Micrognathia (Small Mandible)
Micrognathia may occur in > 700 genetic syndromes.
Pierre Robin sequence is a common manifestation of micrognathia 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). Feeding can be difficult, and sometimes cyanosis develops because the tongue is posterior and may obstruct the pharynx. 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, sewing it to the inner lower lip) may be required. Conductive hearing loss may also be present, so otologic evaluation is indicated.
About one-third of patients with micrognathia have associated anomalies that suggest an underlying chromosomal defect or genetic syndrome. 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 done 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 done 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.
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. 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 done 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 done 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.
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.
