Soft-palate myogenesis: a developmental field paradigm.

Surgical correction of clefts of the soft palate leads to varying degrees of normal function although the repair itself is successful. Explanations for this include structural abnormalities of the muscles. Previous studies have focused primarily on gross anatomical features of late fetal and postnatal cleft palate musculature; however, infrequent reference has been made to early prenatal morphologic patterns of soft-palate development, beginning with the embryo. Thus we evaluated the chronology of prenatal myogenesis of the soft palate from its early mesenchymal phase through the appearance of definitive palatal muscles and associated structures in a sample of 22 human fetuses that represented postfertilization weeks 6.5 to 20.5 (18- to 192-mm crown-rump length). Specimens were histologically prepared for descriptive and morphometric light microscopy. Data were collected on the earliest appearance times of identifiable soft palate and associated structures within the mesenchymal field and on their individual stages of myogenesis (e.g., for muscles, from mesenchyme to myoblasts to fascicles). Analyses showed that (1) palatal muscles and related bony structures emerge sequentially as densely staining mesenchymal subfields within the larger mesenchymal soft-palate field during the 6- to 9-week period, with the tensor veli palatini muscle appearing earliest, and the musculus uvulae latest; (2) further morphogenesis of the soft palate and associated structures follows a definite timeline; and (3) by 16 to 17 weeks the postnatal palatal morphology is in place.