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

Blood supply

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.

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

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

Blood supply of large intestine

Etiology

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

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

Classification

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

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% }

. 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.

. 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

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

. ** 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

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 )

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.

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

Imaging

Imaging Plain abdominal radiography Barium study Angiography CT

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)

SMA thrombosis

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

Barium study

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

. Thick, smooth valvula connivents (black arrows) Interspace spicking (white arrows) Thumbprinting (arrow head)

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

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

. Postischemic stricture , contain pseudodiverticula

CT

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

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

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

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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* pneumatosis intestinalis 6* pneumoperitoneum 7* ascites 8* variable enhancement pattern

. highly suggestive signs: 1- bowel wall thickening with dilatation

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

. 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.

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Differential diagnosis

* 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- Schonlein purpura) 4-bleeding : from hemophilia, thrombocytopenic purpura, anticoagulant therapy, DIC.

illustrated cases

. SBFT shows “stack of coins” small bowel fold pattern due to ischemia,intramural hge.

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

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

. 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.

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

. CT scan shows thickening of the transverse colon . These findings suggest a distribution in superior mesenteric artery territory.

. CT confirms the presence of air in the portal venous system and proximal small bowel mucosal edema. These findings suggest ischemia of the affected bowel.

. Top CT image shows gas in the portal venous system (blue circle). Center image shows thrombosed SMA (blue arrow) . Lower cuts show extensive pneumatosis intestinalis.

SMV thrombosis

Ischemic colitis The enema confirms the appearance of mucosal thickening and localizes the affected bowel to distal transverse colon , splenic flexure and proximal descending colon

Ischemic colitis The enema confirms the appearance of mucosal thickening and localizes the affected bowel to distal transverse colon , splenic flexure and proximal descending colon.

. Pneumatosis coli

. Splenic flexure to descending colon watershed Ischemic colitis

. Abscent enhancement IMA occlusion {left colic bransh}

. SMA embolus

. SMV thrombosis

Ischemic colitis CT image in 22 y old woman with ischemic colitis after blunt abdominal trauma to right flank demonestrate marked thickening of hepatic flexure and right colon, with abrupt transition (arrows) between abnormal and normal wall in the transverse colon.

. Diffuse wall thickening of all colon. 50 y old male Diarrhea, abdominal pain, fever, leukocytosis Antibiotic (cephalosporin) treatment since 2 weeks Pseudomembranous colitis

. Marked low attinuation caecal wall thickening as well as proximal transverse colon with moderate pericolonic inflammatory stranding 45 y old male Bloody diarrhea/ abdominal pain/ fever/vomiting. History of leukemia Neutropenia Typhlitis ( neutropenic colitis)

. 18 y old female Small bowel wall thickening ( not dilated) Mesenteric inflammatory stranding Mesenteric adenopathy Crohn’s disease

. 15 y old boy Circumferential wall thickening of ascending colon Pericolic inflammatory mesenteric fat stranding Crohn’s disease

. Axial CECT shows narrowed lumen and thickened wall of descending colon . Submucosal halo of low density (edema) and engorged blood vessels indicate active disease. Ulcerative colitis

. Axial CECT shows mural thickening of ascending + transvrse colon plus dilated mesenteric vessels. Infectious colitis ( campylobacter colitis)

. Diffuse colonic wall thickness Antibiotic treatment since 10 days Pseudomembranous colitis

. Thumbprinting of transverse colon Ulcerative colitis

. Pancolitis Diffuse wall thickening of all colon Pseudomembranous colitis.

Complications Sepsis Septic shock Multiple system organ failure death

Mortality

. Occlusive mesenteric infarction { embolus or thrombosis } has a 90% mortality rate , whereas non-occlusive disease has a 10% mortality rate . Ischemic enteritis----- 90% mortality rate Ischemic colitis-------- 10% mortality rate

Conclusion

The diagnosis of mesenteric ischemia often is a challenge to both clinicians and radiologists . Patients with inflammatory bowel disease and infectious colitis can present with similar physical signs and symptoms, including cramping abdominal pain ,bloody diarrhea & leukocytosis. Bowel wall thickening is a finding common to all 3 types of disease, however,the pattern of vascular distribution can sometime narrow the differential diagnosis. .

. Ischemic bowel disease is a clinico-radiological diagnosis High clinical suspecion is key to early diagnosis Prognosis depends on underlying cause not imaging.

Many classifications for bowel ischemia { arterial or venous} { occlusive or nonocclusive} { small or large bowel} { acute or chronic} Regardless the mechanism, the disease follows the same course. Clinical picture is very important Vascular supply is important ( location predicts distribution) CT findings are important { highly suggestive & reliable} DD: inflammatory & infectious bowel diseases- diseases causing submucosal hge and edema.

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