The philtrum, or vertical groove in the central part of the upper lip, extends from the base of the nose to the superior aspect of the vermilion border of the lip. In some individuals the philtrum is poorly demarcated, while in others the cutaneous elevations that mark its lateral borders or pillars are easily discernible. The enclosed area is usually depressed. The philtral margins or pillars may be parallel or divergent. Although adequate graphs are available for philtral length, normal philtral width has been of little concern to the clinician; however, increased width and flattening are subjectively established in fetal alcohol spectrum disorder and Cornelia de Lange syndrome.
Clefts involving the upper lip, with or without cleft palate, occur about once in 1000 births, but their frequency varies widely among ethnic groups. Sixty to 80 percent of affected infants are males. The clefts vary from small notches of the vermilion border of the lips to larger divisions that extend into the floor of the nostril and through the alveolar part of the maxilla. Cleft lip can be either unilateral or bilateral. Unilateral cleft lip results from failure of the maxillary prominence on the affected side to unite with merged medial nasal prominences. This is the consequence of failure of the mesenchymal masses to merge and of the mesenchyme to proliferate and push out the overlying endothelium. The result is a persistent labial groove. In addition, the epithelium in the labial groove becomes stretched, and then breakdown of tissues in the floor of the persistent groove leads to division of the lip into medial and lateral parts. Sometimes a bridge of tissue called Simonart's band joins the parts of the incomplete cleft lip.
Bilateral cleft lip results from failure of the mesenchymal masses of the maxillary prominences to meet and unite with the merged medial nasal prominences. The epithelium in both labial grooves becomes stretched and breaks down. In bilateral cases the defects may be similar or dissimilar with varying degrees of defect on each side. In complete bilateral cleft of the upper lip and alveolar processes, the intermaxillary segment hangs free and projects anteriorly. Such defects are especially deforming because of the loss of continuity of the orbicularis oris muscle, which closes the mouth and purses the lips as in whistling.
Median cleft lip is an extremely rare defect of the upper lip caused by a mesodermal deficiency that results in partial or complete failure of the medial nasal prominences to merge and form the intermaxillary segment. The presence of the median cleft lip should alert the observer to look for other midline abnormalities of the brain, including holoprosencephaly.
Other unusual types of facial cleft may occur, but each is individually rare. Oblique facial cleft are often bilateral and extend from the upper lip to the medial margin of the orbit. When this occurs, the nasolacrimal ducts are open grooves. Oblique facial clefts associated with cleft lip result from failure of the mesechymal masses of the maxillary prominences to merge with the lateral and medial nasal prominences. Lateral or transverse facial clefts run from the mouth toward the ear. This abnormality results from failure of the lateral mesechymal masses of the maxillary and mandibular prominences to merge. In severe cases, the cheek is cleft almost to the ear.
Clefts of the lower lip and mandible are also rare. The lip may be cleft superficially or, in severe cases, it may be split down to the chin, involving the mandible.
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