Cleft palate, with or without cleft lip, occurs about once in every 2500 births and is more common in females than males. A cleft may involve only the uvula, giving a fishtail appearance. It may extend through the soft palate, or it may extend all the way forward to the hard palate. The cleft may be overt or submucous. In severe cases associated with cleft lip, the cleft in the palate extends through the alveolar process and lip on both sides. The embryological basis of cleft palate is failure of the mesenchymal masses of the lateral palatine processes to meet and fuse with each other, with the nasal septum, and/or with the posterior margin of the median palatine process or primary palate. Such clefts may be unilateral or bilateral and are classified into three groups:
1. clefts of the anterior or primary palate: clefts anterior to the incisive foramen resulting from failure of the mesenchymal masses of the lateral palatine processes to meet and fuse with the mesenchyme of the primary palate;
2. clefts of the anterior and posterior palate: cleft involving both the primary and secondary palates resulting from the failure of the mesenchymal masses of the lateral palatine processes to meet and fuse with the mesenchyme of the primary palate, with each other, and with the nasal septum;
3. clefts of the posterior or secondary palate: clefts posterior to the incisive foramen, resulting from failure of the mesenchy-mal masses of the lateral palatine processes to meet and fuse with each other and with the nasal septum.
The great majority of cases of cleft palate are associated with multifactorial inheritance. Others are part of single gene or chromosomal syndromes. A few cases appear to be caused by teratogenic agents, particularly anticonvulsants. The fact that the palatine processes fuse about a week later in females than in males may explain why isolated cleft palate is more common among females.
Simple devices have been designed to measure directly palatal height, width, and length. For detailed study, these data may be ascertained from plaster casts. Length of the palate can also be assessed from X-rays. The clinical dysmorphologist may find it easier to use a rough estimate of palate height in the "field." If the maximum height of the palate is greater than twice the height of the teeth, it can be considered abnormal.
Unususally prominent lateral palatine ridges are a nonspecific feature of a variety of disorders in which there is either neuromuscular dysfunction or an anatomic defect that prevents or limits tongue thrust into the palatal vault. The lateral palatine ridges are normally more prominent during prenatal life and infancy. With increasing age they become progressively flattened by the moulding forces of the tongue and usually disappear by five years of age. Prominent lateral palatine ridges may be misinterpreted as a true "narrow high arched palate," which is a much less common anomaly.
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