aganglionic megacolon

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dilatation and hypertrophy of the colon.
Megacolon. From McKinney et al., 2000
acquired megacolon colonic enlargement associated with chronic constipation, but with normal ganglion cell innervation.
acute megacolon toxic megacolon.
aganglionic megacolon (congenital megacolon) Hirschsprung's disease.
toxic megacolon acute dilatation of the colon associated with amebic dysentery or ulcerative colitis; called also acute megacolon.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

Hirschsprung disease

A condition of infant onset characterised by the absence of myenteric nerves in the distal colon, extending proximally from the anus for a variable distance. It affects an estimated 1:5000 live births, and is more common in males (male:female ratio, 4:1); up to 10% have Down syndrome. 

Clinical findings
Failure to pass meconium or stool in first 24 hours post-partum; abdominal distention; vomiting; constipation at birth. Peristalsis is absent in aganglionic segment, causing proximal pseudo-obstruction and gross dilatation, enterocolitis and perforation. In older children, Hirschsprung disease is characterised by chronic constipation, abdominal distention and stunted growth.

By rectal suction biopsy; must include submucosa, taken at least 2 cm above pectinate line.

Resection of aganglionic segment, guided by intraoperative frozen sections from myenteric plexus.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.