1.Trauma to the rectum and anal canal. 2, hemorrhage of the rectum of the anal canal, commonly in the hemorrhage of fecal ulcers. 3, rectal embolism of feces. 4.Perianal abscess and necrotizing fasciitis, including rectal and anal canal foreign bodies. 5.Inset hemorrhoids. 6.Severe anal fissure. 7.Acute necrotizing colitis. 8.Acute obstruction of colorectal tumor. 9.Sigmoid colon torsion.