The diagnosis of congenital megacolon is confirmed by -

(C) (Rectal biopsy) (122 - Bailey and Love 26th)Diagnosis of Hirschsprung's disease (Cong. Megacolon)Digital examination:* On digital examination rectum is empty* Rapid expulsion of faeces often follows examination* Contracted rectal wall can sometimes be appreciated by examining finger.Anorectal manometry:(measure the pressure when balloon is distended in rectum).* Normal individual - Reflex decline in internal sphincteric pressure.* Hirschsrungs disease - Pressure fails to drop, paradoxical rise in pressure with rectal distention.Radiography (Barium enema): demonstrates "presence of transition zone which lies between normal dilated proximal colon and a smaller caliber obstructed distal colon".Rectal biopsy:It is the definitive diagnostic procedure in hirschsprungs disease, it demonstrates.* Hypertrophied nerve bundles* Absence of ganglion cells* Commonest cause colonic obstruction in neonates.* Chronic constipation ( ? not large stool). Males, starting in first few weeks of life.* Loud borboygri (because of intestinal obstruction).* Fecal soiling is not a feature.Causes of Acquired Megacolon:* Chagas disease (caused by protozoan - Trypanoma-cruzi).* Secondary to medications (anticholinergics)* Neurological disorders (Paraplegia, poliomyelitis motor neuron disease, multiple sclerosis)* Rectal cancer*** Defective migration of neural crest cells results.> Albinism> Cong, megacolon> Melanoma> Oropharyngeal teratoma> Elephant man> Neurocristopathies.