What is the normal aganglionic segment of anorectum in adults?

Ultrashort-segment Hirschsprung's disease as a cause of obstructed defecation is controversial because of a lack of knowledge regarding the normal aganglionic zone of the distal rectum. The intent of this study was to define the normal aganglionic zone of the distal rectum through histologic review of cadaveric dissections. Cadavers were obtained from the anatomic pathology laboratory at the University of Massachusetts Medical School. Strip myectomy with overlying mucosa was performed from distal to the dentate line to at least 3 cm into the anal canal and rectum after the pelvis was hemisected. Specimens were fixed in 10 percent buffered formalin. Specimens were sectioned serially every 3 mm and embedded in paraffin. Four-micron slices were then stained with hematoxylin and eosin. Each section was examined by a gastrointestinal pathologist. The presence or absence of nerves and ganglion cells was recorded. Thiry cadavers were obtained for analysis. Mean age at time of death was 79 (range, 65-97) years. There were 13 men. The mean distance of aganglionic bowel from the dentate line was 6.6 (range, 0-21) mm in Meissner's plexus and 5.1 (range, 0-15) mm in Auerbach's plexus. The normal distance of aganglionic bowel wall is 2 cm or less from the dentate line. The absence of ganglion cells proximal to this normal aganglionic zone in the patient with clinical findings of lifelong obstructed defecation defines ultrashort-segment Hirschsprung's disease.