Bowel Ischemia

1. Bowel Ischemia Dr. Ahmed Refaey Consultant radiologist Riyadh Military Hospital MBBCh, MS, FRCR

2. Blood supply

3. Blood supply of small intestine • The entire small intestine is supplied by the superior mesenteric artery and drain to the superior mesenteric vein, which in turn drains to the portal vein.

4. The arterial supply of the colon • That right part of the colon to the midtransverse colon is supplied by the superior mesentric artery • The inferior mesenteric artery supplies the colon as far as the upper rectum

5. Venous drainage of the colon • Veins corresponding with arteries drain to the superior and inferior mesenteric veins.

6. Blood supply of large intestine

7. Etiology

8. Risk factors * atrial fibrillation/flutter * recent acute myocardial infarction * hypovolemia or hypotension ( sepsis ) * coagulation disorders or malignancy * portal hypertension/ cirrhosis * medications - vasopressin-digitalis-beta blockers

9. Pathogenesis • Mesenteric arterial or venous narrowing or occlusion leading to inadequate supply of oxygen to the bowel.

10. Classification

11. Bowel ischemia • Acute or chronic • Occlusive or nonocclusive • Arterial or venous • Small bowel or large bowel . {{ ischemic enteritis or ischemic colitis }}.

12. Acute ischemia • Acute interruption of blood flow to the bowel • causes : @ arterial _ occlusive * embolism {40-50%} : atrial fibrillation or endocarditis (SMA most commonly involved) * thrombosis { 20-40% } : atherosclerosis * mechanical obstruction: strangulation, tumor _ nonocclusive hypoperfusion( low flow states, hypotension, sepsis or heart failure with diffuse mesenteric vasoconstriction ) ( IMA most commonly involved ) @ venous * Mesenteric venous thrombosis { 10% }

13. . • Arterial sources occur more frequently than venous sources by a ratio of 9:1 • Similarly, arterial occlusive disease occur more frequently than nonocclusive disease by a ratio of 9:1 • Large or smaller segments of bowel may be involved, depending on the location of the occlusion • Regardless the mechanism, the disease follows the same course.

14. . • Clinical details : * clinical triad of {sudden onset of abdominal pain, diarrhea & vomiting} * diffuse abdominal pain, out of proportion to physical examination. * leukocytosis * gross rectal bleeding

15. . • Chronic ischemia. { abdominal angina} * * most commonly caused by atherosclerosis of coeliac and SMAs & symptoms are unlikely unless at least two vessels are involved.

16. . ** clinical details * post-prandial abdominal pain, 15-20 minutes after food intake ( due to “gastric steal” diverting blood flow away from intestine ) and the pain subsides 1-2 hours after meal. * fear of eating large meals * malabsorption * weight loss

17. Pathophysiology of bowel ischemia • Mucosa is most sensitive area to anoxia from arterial / venous occlusion with early ulceration, later on necrosis and perforation occur.( of clinical importance ) • Ischemia causes increased permeability of capillaries resulting in both submucosal edema and hemorrhage.( of radiological importance )

18. Ischemic colitis • Most cases are thought to be related to diminished blood flow within the bowel • Predominantly a disease involving the distribution of IMA .i.e., from distal transverse colon to rectum • When the more proximal colon is involved, it is frequently associated with extensive small bowel ischemia & a correspondingly much graver prognosis. • Patients are usually elderly . • The clinical picture may mimic acute diverticulitis. • Most common cause of colitis in elderly & is often self limiting.

19. . • Prognosis of ischemic colitis • complete resolution (75%) within 1-3 months • Stricturing ischemia (20%) • Gangrenous with necrosis and perforation (5%)

20. Imaging

21. Imaging • Plain abdominal radiography • Barium study • Angiography • CT

22. Imaging • Plain abdominal radiograph * abnormal in 20-40% * thumbprinting ( non specific finding, indicating intestinal wall edema with haemorrhage * pneumatosis * PV gas * pneumoperitoneum ( all indicative of bowel infarction)

23. SMA thrombosis

24. . • 81 y old woman with myocardial infarction. Plain abdominal radiograph shows air in the wall of right colon and small & large bowel dilatation.

25. Barium study

26. Barium study * small bowel 1 - thick, smooth valvulaeconniventes. 2 - Barium trapped between the thick folds produces the “ interspacespicking” 3 – (1:2) cm submucosal fluid or blood collections can form, known as “ thumbprinting”

27. . • Thick, smooth valvulaconnivents (black arrows) • Interspacespicking (white arrows) • Thumbprinting (arrow head)

28. .

29. . * large bowel 1- thumbprinting (75%) 2- ulceration 3- loss of interhaustral folds 4- luminal narrowing 5- confined to left hemicolon (90%)

30. . • Segmental narrowing of the entire transverse colon . Within the narrowed segment, there are multiple thumbprinting indentations

31. . • Postischemic stricture , contain pseudodiverticula

32. CT

33. CT • Examination of choice • Sensitivity more than 95% ( MDCT ) • Identifies or excludes other pathologies • Delineates cause,severity and complications. • Guides management

34. Acute ischemia, why CT ? • Plain film– 33% sensitivity – non specific –no information on causes, severity. • Barium study – do NOT do , non-specific, interfere with CT • Angiography – technically difficult, invasive, contraindicated in hypotensive patients

35. CT technique • MDCT “if possible” • Water oral contrast {1000 cc} “ not positive OC “ • IV contrast : 3-5 ml/sec • Arterial and PV phase

36. .

37. CT findings • Suggestive signs 1* “double halo” or “ target” sign. ( edema of the submucosa –low attinuation- with brighter mucosal and serosal surfaces in CECT ) 2* circumferential bowel wall thickening 3* focal / diffuse bowel dilatation 4* increased attinuation of mesenteric fat ( edema ) 5* pneumatosisintestinalis 6* pneumoperitoneum 7* ascites 8* variable enhancement pattern

38. . • highly suggestivesigns: 1- bowel wall thickening with dilatation

39. . • reliablesigns: 1- thromboembolism in mesenteric vessels. 2- lack of enhancement of the ischemic segment of bowel. 3- Portal venous & mural gas.

40. . • A reliable method to differentiate arterial causes from venous causes is depiction of the characteristic bowel wall enhancement pattern. Arterial occlusive disease demonstrate no enhancement of the involved segment, whereas venous occlusive disease or hypoperfusion reveal marked contrast enhancement and retention 2ry to stagnant flow, with thickening of bowel wall.

41. .

42. Differential diagnosis

43. * Causes of intramural edema ( hypoprotinemia, lymphatic blockage 2ry to tumor, inflammatory infiltrate like graft vs host disease and esinophilic enteritis. • Inflammatory bowel disease (Crohn disease-UC) • Infectious bowel diseases • Causes of intramural hemorrhage: 1-ischemia 2-radiation 3-vasculitis –CT disease( SLE, RA,Henoch- Schonleinpurpura) 4-bleeding : from hemophilia, thrombocytopenic purpura, anticoagulant therapy, DIC.

44. illustrated cases

45. . • SBFT shows “stack of coins” small bowel fold pattern due to ischemia,intramuralhge.

47. . • Axial CECT in 23 y old woman with hypercoagulable state + bowel ischemia. Dilated fluid filled small bowel + thrombosis of SMV.

48. . • Axial CECT shows dilates small bowel with areas of wall thickening (arrow). Patient has severe abdominal pain. Bowel infarction from atrial fibrillation.

49. . • Patient with acute ischemia , grossly thickened wall of the splenic flexure and descending colon. There is intraperitoneal air in the subhepatic region & Morrison’s pouch.

50. . • CT demonstrate distension of the caecum. The bowel wall is thickened, and contains multiple small intramural gas bubbles.