Congenital malformations of the oral cavity may involve the lips, jaws, hard palate, floor of mouth, and anterior two thirds of the tongue. These malformations may be the product of errors in embryogenesis or the result of intrauterine events disturbing embryonic and fetal growth. This article begins with a review of the pertinent embryologic development of these structures. After reviewing the normal embryology, specific malformations are described. Recommended management follows the brief description of each malformation. An attempt is made to point out where these malformations deviate from normal development. Finally, management recommendations are based on traditional methods and recent advances described in the literature.
Congenital malformations of the oral cavity may involve the lips, jaws, hard palate, floor of mouth, and anterior two thirds of the tongue. These malformations may be the product of errors in embryogenesis or the result of intrauterine events disturbing embryonic and fetal growth . This article begins with a review of the pertinent embryologic development of these structures. After reviewing the normal embryology, specific malformations are described. Recommended management follows the brief description of each malformation. An attempt is made to point out where these malformations deviate from normal development. Finally, management recommendations are based on traditional methods and recent advances described in the literature.
Embryology
Oral cavity
One can begin to see the early features of facial development by 3 weeks’ gestation. At this time, the pharyngeal arches can be seen bulging out laterally from the embryo. The open ends of the arches face posteriorly and surround the upper end of the foregut and part of the primitive oral cavity or stomodeum. The common wall of the stomodeum and foregut is known as the buccopharyngeal membrane. This membrane is found between the region of the future palatine tonsils and of the posterior third of the tongue. Normally, the buccopharyngeal membrane breaks down at approximately 4.5 weeks’ gestation, establishing the connection between the oral cavity and the digestive tract .
Mandible and maxilla
The first pharyngeal arch, or mandibular arch, begins to grow anteriorly at 3 weeks’ gestation. This arch can be subdivided into a mandibular process below and a maxillary process above. Growth centers become organized at the tips of these arches through neural crest cell migration, vascularization, and mesodermal myoblastic ingrowth. These growth centers are responsible for closing the gap between left and right paired arches . The tips of the mandibular processes fuse at about 4 weeks, forming the mandible and lower lip.
Development of the upper lip and palate involves the maxillary processes and the medial nasal processes, which form at 4 weeks as the nasal pits deepen. The maxillary and medial nasal processes begin to fuse at their lower ends to form the nasal fin. This nasal fin then perforates, and connective tissue flows in to fill the groove between the right and left sides. Through cellular migration upper lip connective tissue increases and slowly fills the groove. By approximately 6 weeks, the maxillary and medial nasal processes have fused in the midline, forming the upper lip and primary palate. The nasal pits deepen until they open into the primitive oral cavity. Palatal embryology is covered in greater detail in the article by Arosarena in this issue.
Tongue
The tongue at 4 weeks has two lateral lingual swellings and one medial swelling, the tuberculum impar. These three swellings originate from the first branchial arch. A second median swelling, the copula or hypobranchial eminence, is formed by mesoderm from the second, third, and part of the fourth arch. As the lateral lingual swellings increase in size, they overgrow the tuberculum impar and merge, forming the anterior two thirds, or body, of the tongue. The posterior one third of the tongue originates from the second, third, and part of the fourth pharyngeal arch. The intrinsic tongue muscles develop from myoblasts originating in occipital somites. The body of the tongue is separated from the posterior third by a V-shaped groove, the terminal sulcus. In the midline of the terminal sulcus lies the foramen cecum, where the thyroid gland appears as an epithelial proliferation between the tuberculum impar and the copula. Later, the thyroid descends anterior to the pharyngeal gut as a bilobed diverticulum. During this migration, the thyroid remains connected to the tongue by a narrow canal, the thyroglossal duct. Normally, this duct later disappears .
Mandibular fusion anomalies
Median mandibular cleft
Clefts of the lower face pass through the midline of the lip and mandible ( Fig. 1 ). Although paramedian lower lip and mandibular clefting have been reported, there are fewer than 70 cases in the literature, appearing with less frequency than the oblique facial clefts. A range of inferior clefting has been reported that extends from mild notching of the lower lip and mandibular alveolus to complete cleavage of the mandible, extending into inferior neck structures. Tongue involvement is typical although variable in expression, ranging from a bifid anterior tip with ankyloglossia to the bony cleft margins, to marked lingual hypoplasia. Inferior cervical defects (midline separation, hypoplasia, and agenesis) of the epiglottis, strap muscles, hyoid bone, thyroid cartilage, and sternum may also be present, particularly when a cutaneous cleft passes caudal to the gnathion of the chin. Median mandibular clefts result from failed coaptation of the free ends of the mandibular processes. As the incisor teeth are frequently missing along the medial mandibular margins, this suggests partial or complete failure of growth center differentiation and development rather than a simple fusion defect .
The lack of a consensus on the nature and timing of corrective surgery for mandibular clefts can be explained by their rarity and variability. Most authors propose correction of the soft tissue structures as soon as possible so as not to cause feeding or speech problems and mandibular bone grafting when the child is 8 to 10 years old to avoid damaging developing tooth buds. Successful management of a complete cleft of the lower lip and mandible in a one-stage procedure in the first 2 years of life has been described, however .
Micrognathia
Micrognathia, literally abnormal smallness of the jaws, usually refers to a small mandible. Decreased mandibular size can occur as an isolated entity or as part of a recognized syndrome. Congenital micrognathia and glossoptosis are most commonly seen in patients who have Robin sequence, but may also be associated with disorders such as Treacher Collins syndrome, Nager syndrome, and hemifacial microsomia. Infants who have Robin sequence typically have a U-shaped palatal cleft secondary to the tongue interfering with closure of the palatal processes during embryogenesis ( Fig. 2 ). Most children born with micrognathia are asymptomatic or can be treated conservatively with prone positioning and nasopharyngeal airways. Still, up to 23% of children who have Robin sequence may have major respiratory obstruction. Tracheotomy is performed in up to 12% of patients who have severe upper airway obstruction related to micrognathia .
Mandell and colleagues recommend mandibular distraction osteogenesis as an alternative to tracheotomy. They concluded that tracheotomy may be avoided in infants who have isolated Robin sequence and that obstructive sleep apnea can be relieved in older micrognathic children. Mandibular distraction osteogenesis is not sufficient to permit decannulation in previously tracheotomized patients who have complex congenital syndromes. Chigurupati and Myall emphasize that most cases of airway obstruction attributable to isolated micrognathia can be managed with surgery. In children who have complete disease, interventions, such as tongue–lip adhesion or tracheotomy, may be preferable to mandibular distraction. Children who have craniofacial microsomia, velocardiofacial syndrome with significant pharyngeal hypotonia, Treacher Collins syndrome, or Nager syndrome may not benefit from distraction during the neonatal period because of frequent airway and temporomandibular joint anomalies.
Mandibular fusion anomalies
Median mandibular cleft
Clefts of the lower face pass through the midline of the lip and mandible ( Fig. 1 ). Although paramedian lower lip and mandibular clefting have been reported, there are fewer than 70 cases in the literature, appearing with less frequency than the oblique facial clefts. A range of inferior clefting has been reported that extends from mild notching of the lower lip and mandibular alveolus to complete cleavage of the mandible, extending into inferior neck structures. Tongue involvement is typical although variable in expression, ranging from a bifid anterior tip with ankyloglossia to the bony cleft margins, to marked lingual hypoplasia. Inferior cervical defects (midline separation, hypoplasia, and agenesis) of the epiglottis, strap muscles, hyoid bone, thyroid cartilage, and sternum may also be present, particularly when a cutaneous cleft passes caudal to the gnathion of the chin. Median mandibular clefts result from failed coaptation of the free ends of the mandibular processes. As the incisor teeth are frequently missing along the medial mandibular margins, this suggests partial or complete failure of growth center differentiation and development rather than a simple fusion defect .
The lack of a consensus on the nature and timing of corrective surgery for mandibular clefts can be explained by their rarity and variability. Most authors propose correction of the soft tissue structures as soon as possible so as not to cause feeding or speech problems and mandibular bone grafting when the child is 8 to 10 years old to avoid damaging developing tooth buds. Successful management of a complete cleft of the lower lip and mandible in a one-stage procedure in the first 2 years of life has been described, however .
Micrognathia
Micrognathia, literally abnormal smallness of the jaws, usually refers to a small mandible. Decreased mandibular size can occur as an isolated entity or as part of a recognized syndrome. Congenital micrognathia and glossoptosis are most commonly seen in patients who have Robin sequence, but may also be associated with disorders such as Treacher Collins syndrome, Nager syndrome, and hemifacial microsomia. Infants who have Robin sequence typically have a U-shaped palatal cleft secondary to the tongue interfering with closure of the palatal processes during embryogenesis ( Fig. 2 ). Most children born with micrognathia are asymptomatic or can be treated conservatively with prone positioning and nasopharyngeal airways. Still, up to 23% of children who have Robin sequence may have major respiratory obstruction. Tracheotomy is performed in up to 12% of patients who have severe upper airway obstruction related to micrognathia .
Mandell and colleagues recommend mandibular distraction osteogenesis as an alternative to tracheotomy. They concluded that tracheotomy may be avoided in infants who have isolated Robin sequence and that obstructive sleep apnea can be relieved in older micrognathic children. Mandibular distraction osteogenesis is not sufficient to permit decannulation in previously tracheotomized patients who have complex congenital syndromes. Chigurupati and Myall emphasize that most cases of airway obstruction attributable to isolated micrognathia can be managed with surgery. In children who have complete disease, interventions, such as tongue–lip adhesion or tracheotomy, may be preferable to mandibular distraction. Children who have craniofacial microsomia, velocardiofacial syndrome with significant pharyngeal hypotonia, Treacher Collins syndrome, or Nager syndrome may not benefit from distraction during the neonatal period because of frequent airway and temporomandibular joint anomalies.
Maxillary fusion anomalies
Cleft lip and palate
As discussed previously, fusion of the components of the upper lip and palate occurs later in embryogenesis and is more complex than that of the lower lip. Clefting anomalies of these structures are therefore more common and more varied. A comprehensive review of cleft lip and palate malformations may be found in the article by Arosarena in this issue.
Nonodontogenic (fissural) cysts
The nomenclature for cysts of the jaws and palate has changed within the past 10 to 15 years. Fissural cysts are now classified as nonodontogenic cysts. Several, including globulomaxillary, median palatal, median alveolar, and median mandibular cysts, are no longer believed to exist. Accepted nonodontogenic cysts include midpalatal cysts of infancy, nasopalatine duct cysts, and nasolabial cysts.
Midpalatal cysts of infancy, or Epstein’s pearls, are keratin-filled cysts that occur in the midpalatine raphe region near the mucosal surface. They are usually seen at the junction of the hard and soft palates in the midline and not seen on the posterior soft palate ( Fig. 3 ). The origin is believed to be epithelial inclusions that persist at the site of fusion of the opposing palatal shelves. They typically number from one to six and are just visible up to 3 mm in diameter. Cysts are noticed at birth or appear after a few days, with new ones appearing up to 2 months, but all of them disappear by 3 months. Management is by observation, because these cysts spontaneously regress. Richard and colleagues caution that a double row of midline palatal cysts may be associated with an underlying submucous cleft palate.
Nasopalatine duct cysts are unilocular, often asymptomatic cysts of the anterior maxilla usually located between the roots of the central incisors. These cysts arise from remnants of the embryonic nasopalatine duct epithelium within the nasopalatine canal. They can produce a heart-shaped radiolucency in a maxillary occlusal radiograph when the anterior nasal spine is superimposed on a central, spherical radiolucency ( Fig. 4 ). Surgical excision of the cyst, which is lined by squamous, respiratory, or both types of epithelium, is curative .
The nasolabial cyst is microscopically similar to nasopalatine duct cysts but is less common and occurs in the soft tissues of the upper lip at the ala of the nose. It was considered a fusional cyst, but is now believed to arise from remnants of the nasolacrimal duct. Treatment is surgical excision .
Oral vestibule anomalies
Labial frenula and oral synechiae
Abnormal labial frenula may involve the upper or lower lips. In infancy, the maxillary labial frenulum typically extends over the alveolar ridge to form a raphe that reaches the palatal papilla. If this persists after the eruption of teeth it may result in a spreading of the medial incisors. Similarly, if the mandibular labial frenulum extends to the interdental papilla, its traction can lead to periodontal disease and bone loss. Each type of aberrant frenulum can be treated with surgical division when clinically significant.
Congenital oral synechiae can occur between the hard palate and floor of mouth, the tongue, or the oropharynx. These are believed to arise from persistence of the buccopharyngeal membrane that separates the mouth from the pharynx in the developing embryo .
Lip pits
Congenital lip pits are rare. Three types are described, based on location: (1) commissural, (2) midline upper lip, and (3) lower lip. They occur either as an isolated defect or in association with other developmental disturbances, such as popliteal pterygium, van der Woude syndrome, oral-facial-digital syndrome, and Marres and Cremers syndromes . Lip pits are depression sinuses lined by stratified squamous epithelium that communicate with minor salivary glands through their excretory ducts. Viscous saliva can be expressed from the pits when pressure is applied. Lip pits may be excised surgically to control infections or for cosmetic reasons .
van der Woude syndrome is an autosomal dominant condition in which lower lip pits are found in combination with cleft lip or palate. The lip pits are bilateral and symmetric paramedian depressions on the vermilion of the lower lip ( Fig. 5 ). Recent genetic studies have shown microdeletions at chromosome bands 1q32–q41 to be the cause of van der Woude syndrome in some families. The trait may be expressed as a submucous cleft palate or the palate may be normal in affected individuals Paramedian lip pits also may be a feature of the popliteal pterygium syndrome, characterized by popliteal webbing (pterygia), cleft lip or cleft palate, genital abnormalities, and congenital bands connecting the upper and lower jaws .
