CT Imaging of Acute Bowel Ischemia and Infarction - Department of ...

CT Imaging of Acute Bowel
Ischemia and Infarction
Randy Fanous
University 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

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 Distribution provides clues to etiology…
• 3. IMA = splenic flexure to rectum
(b) SMA = jejunum, ileum, ascending, transverse
– Anastomotic connections to lumbar arteries (off abdominal aorta) and internal
(c) IMA = descending (rectum spared)
iliacs
• Watershed areas:
– Splenic flexure
– Ileocecal junction
– Rectosigmoid junction
A. Vascular territories
(a) Celiac = duodenum
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
Important to realize that acute bowel
ischemia does NOT refer to a single
– Partial mural necrosis entity, with but possible rather repair a spectrum +/- residual of disease! fibrotic strictures
• 2 = submucosal/ muscularis ischemia
• 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)

Pathology
Etiologies
1. Occlusive (75%):
Arterial (thromboembolism)
2. Non-occlusive (25%):
Venous (bowel obstruction)
• 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.

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
Triple contrast
Triple phased
Triple planar
3 Planes
(a) Axial
(b) Coronal
(c) Sagittal

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. Segmental
Bowel wall thickening vs. thinning
Bowel wall hypoattenuation vs. hyperattenuation
Mucosal hyperenhancement vs. no hyperenhancement

CT
Findings: Approach
• Distribution
– Diffuse
– Segmental
1. Distribution
2. Ischemia = wall thickening, fluid, air
3. Infarction = dilatation, wall thinning, AFL
4. Perforation
• 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

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
Hemorrhage
Bacterial superinfection
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: Air
Pneumotosis
Portal venous gas
Mesenteric 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

Cases
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