SOFT-PALATE MYOGENESIS - A DEVELOPMENTAL FIELD PARADIGM

Surgical correction of clefts of the soft palate leads to varying degr ees of normal function although the repair itself is successful. Expla nations for this include structural abnormalities of the muscles. Prev ious studies have focused primarily on gross anatomical features of la te fetal and postnatal cleft palate musculature; however, infrequent r eference has been made to early prenatal morphologic patterns of soft- palate development, beginning with the embryo. Thus we evaluated the c hronology of prenatal myogenesis of the soft palate from its early mes enchymal phase through the appearance of definitive palatal muscles an d associated structures in a sample of 22 human fetuses that represent ed postfertilization weeks 6.5 to 20.5 (18- to 192-mm crown-rump lengt h). Specimens were histologically prepared for descriptive and morphom etric light microscopy. Data were collected on the earliest appearance times of identifiable soft palate and associated structures within th e mesenchymal field and on their individual stages of myogenesis (e.g. , for muscles, from mesenchyme to myoblasts to fascicles). Analyses sh owed that (1) palatal muscles and related bony structures emerge seque ntially as densely staining mesenchymal subfields within the larger me senchymal soft-palate field during the 6- to 9-week period, with the t ensor veli palatini muscle appearing earliest, and the musculus uvulae latest; (2) further morphogenesis of the soft palate and associated s tructures follows a definite timeline; and (3) by 16 to 17 weeks the p ostnatal palatal morphology is in place.