The severity or extent of the cleft has been related to the period of development of the mandibular process that is affected.
Proposed pathogenesis of median clefts of the lower lip and mandible include, hypoplasia of the mandibular processes either during the early embryonic period or during late embrayonic periods.
This theory explains why all hitherto described congenital parotid fistulas had the fistulous orifice near the oral commissure in the line of the fusion of the maxillary and
mandibular processes. (2,4,5) Hence, the embryologic origin of this anomaly, although related to the branchial apparatus, differs completely from that of the typical branchial cleft fistulas, as well as from that of the ectopic salivary fistulas found at the base of the neck.