Ultrastructural changes in internal anal sphincter in neurogenic faecal incontinence.

The ultrastructural features of the internal anal sphincter (IAS) muscle were studied in biopsies from five patients with neurogenic anorectal incontinence and six control subjects undergoing anorectal excision for cancer, or for inflammatory bowel disease. In the patients with idiopathic neurogenic anorectal incontinence the internal anal sphincter showed loss of smooth muscle cells, disruption of the normal relationships of the remaining cells, stretching of elastic tissue, and increased collagen fibril content. These ultrastructural changes in the morphology of the internal anal sphincter, although probably not the primary cause of faecal incontinence, have functional relevance in the clinical syndrome, as shown by the reduction in resting anal canal pressure found in some patients with this syndrome.