Functional obstruction of the COLON leading to MEGACOLON in the absence of obvious COLONIC DISEASES or mechanical obstruction. When this condition is acquired, acute, and coexisting with another medical condition (trauma, surgery, serious injuries or illness, or medication), it is called Ogilvie's syndrome. The phenotype is colonic pseudo-obstruction (EFO_1000871). Also known as: Colonic Pseudo-Obstruction, primary chronic pseudo-obstruction of colon (disorder).