<s>[INST] context: Hirschsprung's disease - is characterised by the absence of ganglionic cells in the distal colon and rectum - it occurs due to the failure of migration of neural crest cells to distal bowel segments - affects cells in both - myenteric and submucosal plexuses - functional obstruction developes in the affected pa. It can be anatomically divided into four types according to the length of the aganglionic segment: sho segment disease: ~75% rectal and distal sigmoid colonic involvement only long segment:~15% typically extends to splenic flexure/transverse colon total colonic aganglionosis:~7.5% (range 2-13%) also known as Zuezler-Wilson syndrome occasional extension of aganglionosis into the small bowel ultrasho segment disease 3-4 cm of internal anal spinchter only controversial entity - Definitive diagnosis :- by rectal biopsy Barium enema demonstrates cone shape transition zone and reversal of rectosigmoid ratio. Most impoant sign on barium enema is a sudden change of caliber from the narrow aganglionic segment and dilated proximal bowel [/INST] question: Definitive diagnosis of Hirschsprung's disease is done by? | options: A: Rectal Manometry B: Barium enema C: Rectal Biopsy D: Enteroclysis | answer: C </s>