ct imaging of acute bowel ischemia and infarction randy fanous university of toronto pgy3 radiology
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CT Imaging of Acute Bowel Ischemia and Infarction
Randy FanousUniversity of Toronto
PGY3 Radiology
Outline• Anatomy
– Vascular supply of bowel
• Pathology– Stages– Contributing factors– Etiologies
• CT – Technique– Findings
• Cases
Anatomy
Vascular Supply of Bowel: Arterial
• 1. Celiac = distal esophagus to descending duodenum– GDA (first branch of CHA) = anastomotic connections b/w celiac axis and SMA
• 2. SMA = transverse duodenum to splenic flexure– Marginal artery of Drummond/ arcade of Riolan = anastomotic connections b/w
SMA and IMA
• 3. IMA = splenic flexure to rectum– Anastomotic connections to lumbar arteries (off abdominal aorta) and internal
iliacs
• Watershed areas:– Splenic flexure– Ileocecal junction– Rectosigmoid junction
Distribution provides clues to etiology…
A. Vascular territories(a) Celiac = duodenum
(b) SMA = jejunum, ileum, ascending, transverse(c) IMA = descending (rectum spared)
B. Watershed territories
Anatomy
Vascular Supply of Bowel: Venous
• SMV and IMV parallel the corresponding arteries and their drainage
• IMV drains into splenic vein; splenic vein and SMV form portal confluence
• Extensive anastomotic connections b/w mesenteric veins and systemic venous circulation
Bowel is highly vascularized with extensive collaterals (small >> large)
Anatomy
Vascular Supply of Bowel: Blood Flow
• Percentage of cardiac output received by bowel…– (a) Normal circumstances = 20%– (b) Post-prandial (splanchnic auto-regulation) = 35% – (c) Sympathetic stress response = 10%
• Proportion of arterial blood to bowel wall…– 2/3 = mucosa (i.e. susceptible to ischemia)– 1/3 = remainder of the mural layers
Ex. Shock = high-risk group (i.e. low flow state + stress response)
Pathology
Ischemia and Infarction: Stages
• 1 = mucosal ischemia– aka ischemic enteritis/ colitis– Reversible mucosal erosions and ulcerations
• 2 = submucosal/ muscularis ischemia– Partial mural necrosis with possible repair +/- residual fibrotic strictures
• 3 = transmural ischemia – aka bowel infarction– Non-reversible transmural gangrenous necrosis
Pathology
Ischemia and Infarction: Contributing Factors
• 1 = mucosal ischemia– aka ischemic enteritis/ colitis– Reversible mucosal erosions and ulcerations
• 2 = submucosal/ muscularis ischemia– Partial mural necrosis with possible repair +/- residual fibrotic strictures
• 3 = transmural ischemia – aka bowel infarction– Non-reversible transmural gangrenous necrosis
• Post-ischemic inflammatory response– i.e. release of a myriad of cytokines– Contributes to necrosis and further compromises mucosal integrity
• Super-infection (esp. colon)– Translocation of intra-luminal bacteria, leading to mural infection, bacteremia and
sepsis (high mortality)
Important to realize that acute bowel ischemia does NOT refer to a single
entity, but rather a spectrum of disease!
Pathology
Etiologies• Occlusive (75%)
– Mesenteric arterial (90%)• Ex. Thromboembolism (atrial fibrillation, aortic), mesenteric thrombosis, dissection etc.
– Mesenteric venous (10%)• Ex. Neoplasm, infection, hypercoagubility (polycythemia, sickle cell, antithrombin III, protein C/S, oral
contraceptives) etc.
• Non-occlusive (25%)– Mechanical (bowel obstruction)
• (a) Strangulation of mesenteric veins • (b) Over-distension with subsequent compromise of the local mucosal microcirculation
– Hypoperfusion/ Vasospasm• Ex. Shock (hemorrhagic, septic, cardiogenic), severe dehydration, IVDU, pheochromocytoma, familial
dysautonomia etc.
– Inflammatory• Ex. Pancreatitis, appendicitis, diverticulitis, peritonitis etc.
– Vasculopathy• Ex. Vasculitis (i.e. young patients, unusual sites), diabetic vasculopathy, fibromuscular dysplasia etc.
– Others• Ex. XRT, chemotherapy, immunosuppression, corrosive injury etc.
1. Occlusive (75%):Arterial (thromboembolism)
2. Non-occlusive (25%):Venous (bowel obstruction)
CT
Technique: Ischemic Bowel Protocol
3 Types of contrast
(a) IV (150 cc via mechanical injector at a rate of 2-4 ml/sec)
(b) Oral
(c) Rectal
NB: Bowel distension (i.e. assess bowel wall thickness)
NB: Positive vs. negative contrast? Positive contrast indicated in suspected bowel obstruction and advantageous for delineation of
inner mural layer in setting of hypoattenuating mucosa. Otherwise, negative contrast allows optimal delineation of mural layers.
3 Phases
(a) Unenhanced•Differentiating hyperattenuating bowel wall caused by hemorrhage from that caused by hyperperfusion•Background atherosclerotic disease•Hyperattenuating intravascular clot
(b) Arterial (30 sec)•Arterial occlusion
(c) Portovenous (90 sec)•Venous occlusion•Assessment of the remainder of the organs
3 Planes
(a) Axial
(b) Coronal
(c) Sagittal
Triple contrastTriple phasedTriple planar
CT
Findings: Spectrum
• Wide range of CT findings, as expected given the…– range of clinical manifestations– range of severity– range of underlying etiologies– +/- intramural hemorrhage– +/- superinfection
Example:
Diffuse vs. SegmentalBowel wall thickening vs. thinning
Bowel wall hypoattenuation vs. hyperattenuation Mucosal hyperenhancement vs. no hyperenhancement
CT
Findings: Approach
• Distribution– Diffuse– Segmental
• Ischemia– Bowel wall thickening = hypo vs. hyperattenuating; differential wall enhancement– Fluid = fat stranding, mesenteric edema, ascites– Air = pneumotosis, portomesenteric venous gas
• Infarction– Dilatation– Bowel wall thinning– Fluid-filled loops/ AFLs
• Perforation– Pneumoperitoneum– Intralumenal contrast extravasation– Abscess– Peritonitis
1. Distribution2. Ischemia = wall thickening, fluid, air3. Infarction = dilatation, wall thinning, AFL4. Perforation
CT
Findings: Distribution
• i.e. may provide clues to etiology
• (a) Diffuse
• (b) Segmental – Vascular territories– Watershed areas
CT
Findings: Bowel Thickening
• s/t mural edema, hemorrhage, superinfection
• Most SN, least SP (for ischemia, NOT infarction)
• Range of SN = 26-96%– (a) ischemic colitis = 94%– (b) mesenteric ischemia = 80%– (c) bowel infarction = 26-38%
• Occlusive = non-occlusive• Venous >> Arterial
• (a) Hypoattenuating vs. hyperattenuating– Hypoattenuation = edema– Hyperattenuation = hemorrhage
• (b) Differential bowel wall enhancement– i.e. mucosal hyperenhancement
– s/t hyperemia (i.e. reperfusion or superinfection)– SN 33% SP 71%– Produces target sign
CT
Findings: Fluid
• (a) Fat stranding (mesenteric/ pericolonic)• (b) Mesenteric edema• (c) Ascites
• NB: study of SN and SP in non-occlusive venous ischemia (i.e. venous congestion from bowel obstruction)
– (a) Stranding = SN 58%, SP 79%– (b) Edema = SN 88%, SP 90%– (c) Ascites = SN 75%, SP 94%
– NB: 2+ = SP 94%
CT
Findings: Air
• s/t dissection of intra-luminal air s/t loss of mucosal integrity• SP approach 100%
• (a) Pneumotosis– Non-dependent locules– Dissecting wall
• (b) Portomesenteric venous gas– Periphery of liver– Mesenteric vessels
CT
Findings: Infarction
• (a) Bowel dilatation• (b) Bowel wall thinning (i.e. paper thin)
– s/t destruction of intramural nerves and muscles
• (c) AFLs/ fluid-filled (i.e. gasless bowel)– Fluid exudation into the lumen
• NB: SN of dilatation and/or AFL = 56-91% (vs. 40% in ischemia)
CT
Findings: Complications
• Perforation– Pneumoperitoneum– Intralumenal contrast extravasation– Abscess– Peritonitis
References
• Wiesner W, et al. CT of acute bowel ischemia. Radiology 2003; 226:635-650
• Sung RE, et al. CT and MR imaging findings of bowel ischemia from various causes. Radiographics 200; 20:29-42
1. 2678623 = large bowel ischemia
1. 804200566 = large bowel ischemia
2. 2319634 = small bowel ischemia
3. 6270051 = small and large bowel infarction
4. 3259333 = small bowel obstruction with ischemia and perforation
5. 800131666 = ischemic small bowel post-laparotomy that is normal at surgery
Cases
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