Normally the rectum lacks ganglion cells just above the pectinate line. This zone is variable in size but usually is about 2 cm in length. In patients with ultrashort Hirschsprung's disease aganglionosis involving rectum less than 2 cm from the pectinate line is associated with chronic constipation.
Typical forms:
(1) short segment (67-82% of patients)
(1a) rectum
(1b) rectum and sigmoid colon
(2) colonic segment: rectum, sigmoid colon and descending colon
(3) long segment (15-25%)
(3a) rectum, sigmoid colon, descending colon and transverse colon
(3b) rectum, sigmoid colon, descending colon, transverse colon, ascending colon
(3c) rectum, sigmoid colon, descending colon, transverse colon, ascending colon, cecum
Variants:
(1) total colonic aganglionosis (3-8%): entire colon plus distal terminal ileum
(2) ultrashort (rare): involves the distal rectum below the pelvic floor. These patients often present as adults with a history of chronic constipation. The aganglionic segment is at or within 2 cm of the pectinate line, so is in the region where aganglionosis is normally expected.
(3) entire bowel (rare)
