Small bowel ischemia is an acute or chronic condition resulting from inadequate blood supply to the bowel wall. Acute mesenteric ischemia (AMI) is a surgical emergency with mortality reaching 60-80%. The most common cause is superior mesenteric artery (SMA) embolism (40-50%) or thrombosis (20-30%); non-occlusive mesenteric ischemia (NOMI) and mesenteric vein thrombosis (MVT) are other causes. The ischemic process progresses from mucosa to serosa — early stages show mucosal damage and hemorrhage, while advanced stages develop transmural necrosis, perforation, and peritonitis. CT angiography is the gold standard for diagnosis, and early diagnosis is lifesaving. Pneumatosis intestinalis, portal venous gas, and paper-thin wall are findings of advanced ischemia/necrosis.
Age Range
50-90
Peak Age
70
Gender
Equal
Prevalence
Uncommon
Mesenteric ischemia develops from decreased or interrupted arterial blood flow to the bowel wall. In SMA embolism, typically a cardiac-origin thrombus (atrial fibrillation, mural thrombus, valvular disease) embolizes from the aorta to the SMA, usually occluding 3-8 cm distal to the SMA origin, just beyond the middle colic artery takeoff — therefore, the proximal jejunum is spared while the distal jejunum and ileum are affected. In SMA thrombosis, thrombus develops on an atherosclerotic plaque, usually occluding at the SMA origin. The ischemic cascade starts from the mucosa because the mucosa is the most metabolically active layer and most sensitive to hypoxia. Within the first 2 hours, mucosal edema and hemorrhage develop; after 6 hours, the submucosal and muscular layers are involved; after 12 hours, transmural necrosis occurs. On CT, early stages show bowel wall thickening and hyperemia (increased enhancement), while advanced stages show decreased enhancement (paper-thin wall), pneumatosis intestinalis (mucosal barrier loss → intraluminal gas enters the wall), and portal venous gas. In NOMI, there is no vascular occlusion — segmental ischemia develops due to splanchnic hypoperfusion from low cardiac output, shock, or vasoconstrictor medications.
Non-enhancing, markedly thinned bowel wall (paper-thin wall) with intramural gas collection (pneumatosis intestinalis) in the small bowel — pathognomonic findings of advanced transmural necrosis. When portal venous gas accompanies, the picture is complete and mortality rises to 75-90%.
Filling defect in SMA lumen on CT angiography — intravascular thrombus or embolus. In embolism, typically abrupt occlusion 3-8 cm distal to SMA origin, beyond middle colic artery takeoff; in thrombosis, irregular occlusion at SMA origin or proximal segment with atherosclerotic calcifications. Decreased or absent enhancement of distal SMA branches. In embolism, normal enhancement proximal to occlusion is present ('meniscus sign').
Report Sentence
Filling defect in the SMA lumen on CT angiography is consistent with acute mesenteric ischemia; decreased distal perfusion is present.
Markedly thinned (paper-thin), non-enhancing or minimally enhancing bowel wall in the affected small bowel segment on portal venous phase — transmural necrosis finding. Normal bowel wall thickness is 1-3 mm while necrotic wall thins to <1 mm. The affected segment is typically dilated and filled with gas and fluid. Distinctly different from adjacent normal segments.
Report Sentence
Segmentally markedly thinned and non-enhancing bowel wall (paper-thin wall) in the small bowel is consistent with transmural ischemia/necrosis.
Pneumatosis intestinalis — gas collections within the bowel wall. May be in linear (smooth curvilinear) or cystic (small bubble) pattern. In the context of ischemia, linear pattern is more common. Intramural gas represents passage of luminal gas into wall layers through necrotic mucosa. This finding strongly suggests transmural necrosis and indicates surgical urgency.
Report Sentence
Intramural gas (pneumatosis intestinalis) in the small bowel is consistent with advanced mesenteric ischemia/necrosis, and urgent surgical evaluation is recommended.
Portal venous gas — branching hypodense gas foci in the liver periphery. Intraluminal gas in portal vein and branches. This finding represents gas passing from the necrotic bowel wall into mesenteric veins and then into the portal system. It is an extremely poor prognostic finding indicating advanced bowel necrosis. When evaluated with pneumatosis intestinalis, the need for surgical intervention is confirmed.
Report Sentence
Branching portal venous gas in the liver periphery is a poor prognostic finding consistent with advanced bowel necrosis.
Bowel wall thickening (>3 mm) and increased enhancement (hyperemia) in the affected segment in early stage — reperfusion injury or reversible ischemia finding. Wall thickening results from edema and hemorrhage. Mucosal enhancement is increased because vascular permeability increases during ischemia-reperfusion. This finding is also known as 'target sign' (wall thickening) pattern — outer hypodense edema ring and inner enhancing mucosa.
Report Sentence
Segmental bowel wall thickening and increased mucosal enhancement in the small bowel are consistent with early-stage mesenteric ischemia.
Mesenteric vein thrombosis (MVT) — filling defect and venous wall thickening in superior mesenteric vein (SMV) or its branches. In MVT, bowel wall thickening is more prominent with a hemorrhagic infarction pattern. Mesenteric edema ('misty mesentery') is accompanying. Ascites is common. Has a slower course than arterial ischemia but can progress to transmural necrosis.
Report Sentence
Filling defect in the superior mesenteric vein with prominent bowel wall thickening in the affected segment is consistent with mesenteric vein thrombosis and venous ischemia.
Criteria
Cardiac-origin thrombus embolization to SMA — most common cause (40-50%)
Distinct Features
Sudden onset, occlusion 3-8 cm distal to SMA origin, proximal jejunum spared, atrial fibrillation history, 'meniscus sign'
Criteria
In-situ thrombus formation on atherosclerotic plaque — 20-30% of cases
Distinct Features
Slower onset, occlusion at SMA origin, entire small bowel may be affected, atherosclerosis risk factors, may have history of chronic mesenteric ischemia (intestinal angina)
Criteria
No vascular occlusion — segmental ischemia due to splanchnic hypoperfusion
Distinct Features
In critically ill patients (shock, heart failure), vasoconstrictor use, SMA/SMV patent on CT but diffuse/segmental bowel wall changes, watershed areas affected
Criteria
Thrombus in SMV or its branches — 5-15% of cases
Distinct Features
Slower onset, prominent wall thickening (hemorrhagic infarction), ascites, 'misty mesentery', thrombophilia risk factors (OCP, portal HT, surgery)
Distinguishing Feature
In Crohn's disease, segmental wall thickening is due to chronic inflammation; enhancement is preserved (increased), with skip lesions, fistula, abscess, and 'comb sign.' In ischemia, enhancement is decreased and vascular occlusion is present.
Distinguishing Feature
In radiation enteritis, history is critical (pelvic/abdominal RT). Wall thickening is diffuse and corresponds to radiation field. No vascular occlusion. In subacute/chronic form, mesenteric fat increase and tethering are seen.
Distinguishing Feature
In angioedema, segmental bowel wall thickening and submucosal edema are seen but without vascular occlusion; ascites and 'accordion sign' may accompany. ACE inhibitor use or hereditary angioedema history is distinguishing.
Distinguishing Feature
In adhesive SBO, mechanical obstruction findings are present but bowel wall enhancement is preserved (if no ischemia). No vascular occlusion finding. Caliber change at transition point consistent with band/adhesion is seen.
Urgency
emergentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralAcute mesenteric ischemia is a surgical emergency — early diagnosis and intervention significantly reduce mortality. In SMA embolism, embolectomy or thrombolytic therapy; in SMA thrombosis, surgical revascularization; necrotic bowel resection may be needed. In NOMI, treatment of underlying cause and vasodilator infusion; in MVT, anticoagulation is the mainstay. 'Second-look' laparotomy is considered at 24-48 hours.
Mesenteric ischemia is an emergency with high mortality. Transmural necrosis signs (pneumatosis, portal venous gas, loss of enhancement) require emergency surgery. CT angiography is critical for early diagnosis. Atrial fibrillation and atherosclerosis are risk factors.