Infantile hypertrophic pyloric stenosis: myopathic type.

Smooth muscle cell biopsies obtained at pyloromyotomy from 37 children with infantile hypertrophic pyloric stenosis (IHPS) were studied by light and electron microscopy and compared with 6 autopsy control cases without any clinical evidence of this disorder. In cases with IHPS an apparently irregular increase in the number of smooth muscle cells by mitosis was accompanied by an increase of the endoplasmic reticulum, proliferation of mitochondria and regressive changes, such as shrinkage, swelling, necrosis and apoptosis of smooth muscle cells. Other alterations, seen in some but not all cases consisted of large numbers of unusual dense granules some of which were clearly associated with actin filaments and, therefore, regarded as derivatives of the normally occurring dense bodies. Furthermore, intermyofibrillar and subsarcolemmal glycogen accumulations, various nuclear abnormalities and pleomorphic membranous cytoplasmic or nuclear bodies occurred. While smooth muscle cell abnormalities predominated in some cases of IHPS, in others there were more severe axonal changes in the myenteric plexus. It is suggested, therefore, that a primarily myogenic type of IHPS can be distinguished from a predominantly neurogenic type.