This section is from the book "A Manual Of Pathology", by Guthrie McConnell. Also available from Amazon: A Manual Of Pathology.
Volvulus is the twisting of the intestine resulting in obstruction. It may twist in its long axis, but usually a loop of intestine twists around its mesenteric attachment. It occurs where the mesentery is unusually long and lax. The most common seat is in the sigmoid flexure. In volvulus there is a consequent obstruction to the blood-supply, and if the condition is not rapidly remedied, thrombosis, edema, and gangrene ensue. Above the twist the intestine will be dilated, there will be passive congestion, and frequently ulceration with perforation. Sometimes adhesions may form with a neighboring loop of intestine and no peritonitis result.
Intussusception or invagination is a condition in which one part of the intestine slips into the lumen of an adjoining part, like a glove-finger. The outer covering is called the intussuscipiens or sheath; the inner portion, the intussusception. Is most frequent in young babies and most common near the ileocecal valve. It may be due to convulsive or to reverse peristalsis. In children there may be found at the post-mortem table numerous invaginations which probably occurred during the death agony and have no significance.
The ensheathed portion may be very short or it may extend many feet. As a result of the invagination peristalsis is increased and the tendency is for the intussusception to become greater and greater. As the intestine is invaginated the mesentery is taken with it and the circulation is interfered with. That is followed by congestion, edema, and inflammation; a result of which is the formation of adhesions rendering the displacement permanent. If the process has been more acute, obstruction with gangrene and peritonitis usually follows. Sometimes the invaginated portion may slough off, be passed through the rectum, and the edges of the intestine unite without any peritonitis resulting. There may be merely a stenosis through which fluid contents can pass.
Occasionally the rectum may extrude from the anus - prolapse. It usually occurs as a result of strained defecation. Is generally very easily reduced, but is likely to recur-as the sphincter muscle is usually weak. If allowed to remain, the prolapsed portion becomes inflamed, the mucous surface ulcerated, and necrosis may occur, as a result of acute strangulation by constriction of the sphincter.