The relationship between the morphology of the levator muscle and the function of velopharyngeal closure or clarity of speech in patients with submucous cleft palate or congenital velopharyngeal imcompetence was investigated with an enzyme histochemical technique. The ultrastructure of the levator muscles was examined by transmission electron microscopy. The muscle fibers in the levator muscles of patients with these two diseases were classified into three types, red, white and intermediate, by SDH staining.
Levator muscle with excellent velopharyngeal closure function or with those in patients with excellent speech contained red fibers. Poorly aligned muscle fibers with a wide range of diameters have been recognized in these two diseases. The histogram of the diameter of muscle fiber showed a wide spread and unimodal distribution pattern. The diameter of muscle fibers tends to be increased in patients with superior function of velopharyngeal closure or in old age. In patients with congenital velopharyngeal incompetence, however, small fibers are seen. Ultrastructural investigation revealed that the levator muscles in these two diseases consist of either normal or degenerative muscle fibers with misaligned myofibrils or vacuolation. Signs of necrosis, such as hypercontraction of myofibrils and degeneration of the nucleus and regeneration with central nuclei were also noted, suggesting segmental necrosis of muscle cells and the possibility of regeneration.
