<unk>  is an abnormal dilatation of the colon (a part of the large intestines) that is not caused by mechanical obstruction. The dilatation is often accompanied by a paralysis of the peristaltic movements of the bowel, resulting in chronic constipation. In more extreme cases, the feces consolidate into hard masses inside the colon, called fecalomas (literally, fecal tumor), which require surgery to be removed.
A human colon is considered abnormally enlarged if it has a diameter greater than 12 cm in the cecum, greater than 6.5 cm in the rectosigmoid region and greater than 8 cm for the ascending colon 
A<unk>  can be either acute or chronic. It can also be classified according to etiology.
Megacolon
Fecal impaction
Vesicointestinal fistula
Rectal foreign body
Pseudomembranous enterocolitis
Toxic megacolon
Imperforate anus
Fecaloma