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)

Pathology

Etiologies: Occlusive

IMA atherosclerosis

Pathology

Etiologies: Occlusive

SMA thromboembolism

Pathology

Etiologies: Occlusive

SMA Cholesterol embolus

Pathology

Etiologies: Occlusive

Aortic stent occlusion of IMA

Pathology

Etiologies: Occlusive

Polycythemia ruba vera

Pathology

Etiologies: Non-occlusive

Cardiogenic shock

Pathology

Etiologies: Non-occlusive

Lupus

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: Bowel Thickening

Edema

Target signBacterial superinfection

Hemorrhage

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: Air

Pneumotosis

Mesenteric venous gas

Portal venous gas

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

Cases

Case #1

Cases

Case #1: Large bowel ischemia

Cases

Case #2

Cases

Case #2: Large bowel ischemia

Cases

Case #3

Cases

Case #3: Small bowel Ischemia

Cases

Case #4

Cases

Case #4: Small and large bowel infarction

Cases

Case #5

Cases

Case #5: Small bowel obstruction with ischemia and perforation

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