Page 579 - Textbook of Pathology, 6th Edition

as ischaemic bowel disease. In either case, the cause of 563
ischaemia is compromised mesenteric circulation, while
ischaemic effect is less likely to occur in the stomach,
duodenum and rectum due to abundant collateral blood
supply.
Depending upon the extent and severity of ischaemia, 3
patterns of pathologic lesions can occur (Fig. 20.22):
1. Transmural infarction, characterised by full thickness
involvement i.e. transmural ischaemic necrosis and gangrene
of the bowel.
2 Mural infarction, characterised by haemorrhagic gastro-
enteropathy (haemorrhage and necrosis). The ischaemic
effect in mural infarction is limited to mucosa, submucosa
and superficial muscularis, while mucosal infarction is
confined to mucosal layers superficial to muscularis
mucosae.
Figure 20.21 Ileocaecal intussusception. 3. Ischaemic colitis, due to chronic colonic ischaemia causing
fibrotic narrowing of the affected bowel.

When the blood flow in the hernial sac is obstructed, it These pathologic patterns are described below:
results in strangulated hernia. Obstruction to the venous
drainage and arterial supply may result in infarction or Transmural Infarction
gangrene of the affected loop of intestine. The gross and Ischaemic necrosis of the full-thickness of the bowel wall is
microscopic appearance of strangulated intestine is the same more common in the small intestine than the large intestine.
as that of infarction of intestine.
ETIOPATHOGENESIS. The common causes of transmural CHAPTER 20
Intussusception infarction of small bowel are as under:
i) Mesenteric arterial thrombosis such as due to the following:
Intussusception is the telescoping of a segment of intestine
into the segment below due to peristalsis. The telescoped Atherosclerosis (most common)
segment is called the intussusceptum and lower receiving Aortic aneurysm
segment is called the intussuscipiens. The condition occurs Vasospasm
more commonly in infants and young children, more often Fibromuscular hyperplasia
in the ileocaecal region when the portion of ileum invaginates Invasion by the tumour
into the ascending colon without affecting the position of Use of oral contraceptives
the ileocaecal valve (Fig. 20.21). Less common forms are ileo- Arteritis of various types
ileal and colo-colic intussusception. ii) Mesenteric arterial embolism arising from the following
In children, the cause is usually not known though causes: The Gastrointestinal Tract
enlargement of the lymphoid tissue in the terminal ileum Mural thrombi in the heart
has been suggested by some. In the case of adults, the usual Endocarditis (infective and nonbacterial thrombotic)
causes are foreign bodies and tumours.
The main complications of intussusception are intestinal Atherosclerotic plaques
obstruction, infarction, gangrene, perforation and peritonitis. Atrial myxoma
iii) Mesenteric venous occlusion is less common cause of full-
Volvulus thickness infarction of the bowel. The causes are as under:

Volvulus is the twisting of loop of intestine upon itself
through 180° or more. This leads to obstruction of the
intestine as well as cutting off of the blood supply to the
affected loop. The usual causes are bands and adhesions
(congenital or acquired) and long mesenteric attachment. The
condition is more common in the sigmoid colon than the
small bowel.

ISCHAEMIC BOWEL DISEASE
(ISCHAEMIC ENTEROCOLITIS)
Ischaemic lesions of the gastrointestinal tract may occur in
the small intestine and/or colon; the latter is called ischaemic Figure 20.22 Schematic diagram to show the three types of
colitis or ischaemic enterocolitis and is commonly referred to ischaemic bowel disease depending upon the extent of involvement.