Median Cleft of the Lower Lip and Mandible: Case Reports, a New Embryologic Hypothesis, and Subdivision

Abstract

Median clefts of the lower lip and mandible are rare. In the literature so far, about 62 cases have been described. In addition, three more patients are presented here. These cases show a broad variation in the severity of this deformity, ranging from a simple notch in the vermillion to a complete cleft of the lip involving the tongue, the chin, the mandible, the supporting structures of the median of the neck, and the manubrium sterni. Several hypotheses concerning the pathogenesis of median clefts of the lip and mandible have been proposed. Most authors consider it to be a failure of fusion of the first pair of branchial arches or failure of mesodermal penetration into the midline. From our embryologic point of view, however, instead of paired branchial arches, only one first branchial arch develops during the early embryonic period (< or = 17 mm crown-rump length). Within this first branchial arch, two mandibular processes grow out, separated by a groove in the median. These mandibular processes do not fuse but merge during the late embryonic period (> or = 17 mm to < or = 60 mm crown-rump length). In the same developmental period, there is formation of the lip and the alveolar process and the anlage and outgrowth of one membrane bone center in each mandibular process, resulting in the formation of the mandible with its symphysis. As a consequence of the preceding, we propose the following subdivision of the median clefts of the lip and/or mandible: Hypoplasia of the mandibular processes during the early embryonic period will lead to the severest cleft of the mandible extending into the neck. During the late embryonic period, the less severe median clefts will develop. Disturbances of the outgrowth of bone centers of the mandible, resulting in nonformation of its symphysis, cause clefting of the mandible with involvement of all related soft tissues. Defects in the merging process produce just a notch of the vermilion or a higher cleft of the lower lip with or without involvement of the alveolar process of the mandible. In conclusion, the variety of the clefts in the median of the lower lip and/or mandible as well as the low rate of incidence can be explained by the embryologic hypothesis proposed here.

Characterization of the fate of midline epithelial cells during the fusion of mandibular prominences in vivo

“…Median clefts of the lip and mandible result from a failure of fusion of the first branchial arch derived paired mandibular prominences, and/or failure of mesenchymal cell penetration into the midline. The severity of the mandibular cleft defects depends upon the developmental stage at which the fusion of mandibular prominences was disturbed (Oostrom et al, 1996). Significantly, the cellular, molecular, and developmental processes controlling fusion of mandibular prominences have not been determined.…”

Medial tongue cleft associated with intraoral hamartoma—case report and review of literature

“…Type 30 clefts show a variation from the lower lip to the suprasternal region 15 . Most authors consider this to be a failure of fusion of the first pair of branchial arches or failure of mesodermal penetration into the midline 4,13 . The current literature reports no median tongue clefts without an association with median mandibular or lip clefts.…”

Tessier 30 Facial Cleft- Median Cleft of Upper and Lower Lip, Lower Alveolus and Mandible, Ankyloglossia and Cervical Teratoma

“…In 1996, Oostrom et al proposed that only one branchial arch during early embryonic period (7th week) into which two mandibular processes grow with a groove in midline. Defect in early embryonic period will lead to severe cleft of the mandible extending into the neck whereas in late embryonic period will lead to median clefts with less severity [5]. Deformity can range from minor to severe variety and in various combinations.…”