<prompt> Aganglionic segment is encountered in which pa of colon in case of Hirschsprung disease ?Distal to dilated segmentIn Whole colonProximal to dilated segmentIn the dilated segment  <response>: Ans. is a i.e., Distal to dilated segment Congenital aganglionic megcolon Hirschsprung disease o Hirshsprung disease a congenital disorder characterized by aganglionosis of a poion of the intestinal tract. o An intestinal segment lacks both Meissner submucosal and Auerbach myenteric plexuses. This leads to functional obstruction and intestinal dilation Proximal to the affected segment. o Histological findings are :- i Absence of ganglion cells and ganglia in the muscle wall and submucosa of the affected segment. ii Thickening and hyperophy of nerve trunk. o Rectum is always affected with involvement of more proximal colon to variable extent -- most cases involve the rectum and sigmoid only. o Proximal to the aganglionic segment, the colon undergoes progressive dilation and hyperophy. o With time, the proximal innervated colon may become massively distended -- megacolon. 