Embryological approach to philtral hair sparsity in bilateral cleft lip deformities.

Objective: In bilateral cleft lip cases, surgeons have long known that the medial nasal prominence or prolabium is devoid of muscle. Despite cheiloplasty restoring orbicular muscle continuity, moustache hair growth is less developed on the philtral skin. We sought to understand this hair disparity.

Basic Procedures: The authors conducted a comprehensive literature search using reference materials on the physiological and pathological development of the face in utero and the PubMed database using the keywords 'embryology', 'bilateral cleft lip' and 'hair'.

Main Results: In bilateral cleft lip, the normal fusion between the maxillary and intermaxillary process does not occur, and the migration of cranial neural crest cells (CNCC) is disturbed. CNCCs from different locations and with different myoblastic differentiation potential are arrested on each side of the cleft. Therefore, a reduced concentration of myoblasts and myocytes as well as hormone receptors in the medial process could hinders the normal physiological development of the different layers of the philtral skin and especially the skin appendages.

Conclusion: Philtral hair sparsity in patients with bilateral cleft lip can be explain by a defect in the migration of CNCCs to the prolabium, whose cells are not able to develop hair follicles, due to a disruption of the exchange of Wnt/β-catenin, EDA, and or Noggin signals and due to the absence of androgen receptor.