The Anatomy of Cupidʼs Bow in Normal and Cleft Lip

Abstract

This is a gross and microscopic examination of the cutaneous-vermilion-mucosal region (Cupid's bow) in infants with normal lip as compared to cleft lip. Morphologic observations of lips in situ were made with magnification. Specimens for histology were from the normal upper lip of infants (n = 3) and adults (n = 4), and from redundant tissue made available during primary repair of cleft lip (n = 13) and cleft lip revision (n = 4). Tissues were analyzed with hematoxylin and eosin, Gomori trichrome, and Fontana-Masson stains. Immunoperoxidase stains were used to emphasize vascular endothelium and epithelial cytokeratins. Our observations support the hypothesis that the anterior projection of the pars marginalis of the musculus orbicularis oris gives rise to the normal cutaneous-vermilion junction ("white skin roll" of Gillies-Millard). The band of vellus hairs, found atop the vermilion-cutaneous junction, also highlights the rim of Cupid's bow. There was no abrupt alteration in vasculature, melanin, or cytokeratin content in the white roll. Proceeding caudally, the vermilion-mucosal region was characterized by progressively increasing epidermal thickness and size of rete ridges, decreasing melanin, more superficial capillaries, and an abrupt transition from keratinized to nonkeratinized squamous epithelium ("red line" of Noordhoff). In the cleft lip specimens, where white roll was absent, there was hypoplasia and disorientation of the underlying pars marginalis component of m. orbicularis oris. Vellus hair follicles were seen in the zone of presumptive white roll in clefts, just as in normal lip. Frequently, these pilar units contained disproportionately large sebaceous glands. In some cleft lip specimens, ectopic sebaceous glands were noted in the oral mucosa. We also observed a deficiency of vermilion width on the medial side of unilateral cleft lip, whereas the width of the vermilion at the crest of the bow was normal or slightly increased in the lateral cleft segment. A narrow vermilion band and exposed hypoplastic mucosa were characteristic of the prolabium in the bilateral complete cleft deformity. The findings of this study are pertinent to technical details for construction of the Cupid's bow and vermilion in unilateral and bilateral cleft lip.