Ultrastructural observations of the myenteric plexus of the pylorus in infantile hypertrophic pyloric stenosis.

Myenteric plexuses and smooth muscle of the pylorus obtained by biopsy at pyloro myotomy in 5 infants with hypertrophic pyloric stenosis were studied by electron microscopy. Animal controls consisted of pyloruses from 2 infant and 2 adult rabbits and 2 adult rats. The principal findings in the plexuses of the patients were moderate numbers of variably sized, swollen degenerating axons that contained dense bodies, lamellated figures, vacuoles, granular or fibrillar material, and swollen mitochondria. The significance of this alteration in the etiology and pathogenesis of this disorder is not clear. Neurons in the plexuses showed no definite abnormalities. Although these findings do not confirm previous light microscopic observation of neuronal changes in the pyloric myenteric plexuses, they do not exclude a neurogenic mechanism for this disorder. The presence of small immature neurons and large mature neurons suggests that neuronal maturation and development in infantile hypertrophic pyloric stenosis are not impaired as previously reported. No ultrastructural changes were found in interstitial cells of the myenteric plexuses. Except for hypertrophy of the circular smooth muscle layers, no specific alterations were found in muscle fibers of the pylorus.