Etiology

Arterial compromise

  • Embolism

    • Embolic arterial obstruction accounts for 40% to 50% of acute mesenteric ischemia; most commonly affecting the superior mesenteric artery.[17][18] The embolus usually originates from a left-sided heart thrombus, or from spontaneous or iatrogenic rupture and embolization from an aortic atherosclerotic plaque or aneurysm.[19][20][21] Interventional radiologic procedures are the most common cause of iatrogenic plaque rupture.

  • Thrombosis

    • About 15% to 20% of acute mesenteric ischemia results from thrombus occurring as a progression of atherosclerosis at the origin of the superior mesenteric artery.[19][22] Mesenteric atherosclerotic plaques may rupture with associated acute thrombosis of the vessel. Subacute or chronic ischemia may result from partial occlusion of the vessel.

  • Vasculitis

    • Rheumatoid arthritis, polyarteritis nodosa, systemic lupus erythematosus, dermatomyositis, Takayasu arteritis, and thromboangiitis obliterans can all result in ischemia of the bowel. The exact clinical picture varies depending upon factors such as the size of the mesenteric vessel involved.

  • External compression

    • Rarely, extrinsic compression of the celiac axis can lead to mesenteric ischemia, usually due to the median arcuate ligament of the diaphragm and surrounding nerve plexus impinging onto the celiac axis.[17] It occurs more often in women than in men.[23]

    • Tumors and other masses within the abdomen can also surround and ultimately compress blood vessels supplying the bowel, causing ischemic damage.

  • Vasospasm[17]

Venous compromise

  • Venous thrombosis[17]

    • Accounts for 5% to 15% of cases of acute mesenteric ischemia.[1][18] Frequently involves the superior mesenteric vein.

    • Usually associated with cirrhosis or portal hypertension; other potential associations include inheritable hypercoagulable states (e.g., factor V Leiden, protein C deficiency, prothrombin G20210A mutation), pancreatitis, malignancy, oral contraceptive use, and recent surgery. Approximately half of patients presenting with venous thrombosis have had a prior history of deep vein thrombosis or pulmonary embolus.[18][23]

Hypoperfusion (i.e., nonocclusive ischemia)[17]

  • Accounts for as much as 20% of cases of acute mesenteric ischemia.[24] Associated with high mortality (between 30% and 93%).[17]

  • Features include shock and hypotension.[17] Relative mesenteric hypotension may also be present (from any etiology). Prominent causes include:

    • Heart failure.

    • Hemodialysis (renal failure).[11]

    • Drug-related

      • Such as digitalis, estrogen, contraceptives, vasopressin, vasopressors, danazol, flutamide, glycerin enema, alosetron, immunosuppressives, psychotropics, imipramine, pseudoephedrine, sumatriptan, nonsteroidal anti-inflammatory drugs, ergot, diconal, laxatives, pegylated interferon, methamphetamines, cocaine.[25][26]

    • Recent surgery or trauma

      • Such as aortic aneurysm repair, aortoiliac bypass, colectomy, colonoscopy.

      • Increased risk with enteral nutrition in postsurgical or trauma patients in intensive care.[24]

    • Infection

      • Such as cytomegalovirus, hepatitis B, Escherichia coli O157:H7.

    • Other

      • Such as pancreatitis, polycythemia vera, pheochromocytoma, carcinoid syndrome.

Pathophysiology

The small intestine receives blood via the celiac artery and the superior mesenteric artery (SMA). The colon receives blood via the SMA and the inferior mesenteric artery (IMA). The rectum also receives blood via branches of the internal iliac artery. Several collateral arteries exist between the SMA and the IMA, including the marginal artery of Drummond and the arc of Riolan. The splenic flexure and the rectosigmoid junction are two watershed areas where collateralization of blood flow may be limited. [Figure caption and citation for the preceding image starts]: Distribution of blood flow to the colon originating from the inferior mesenteric artery, branches of which include the left colic, marginal, and sigmoid arteries and supply the left colon and superior portion of the rectumBMJ 2003; 326 doi: 10.1136/bmj.326.7403.1372 [Citation ends].Distribution of blood flow to the colon originating from the inferior mesenteric artery, branches of which include the left colic, marginal, and sigmoid arteries and supply the left colon and superior portion of the rectum[Figure caption and citation for the preceding image starts]: Distribution of blood supply to the small intestine and colon from the superior mesenteric artery, branches of which include the middle, right, and ileocolic arteries as well as jejunal and ileal arteries and arteriolesBMJ 2003; 326 doi: 10.1136/bmj.326.7403.1372 [Citation ends].Distribution of blood supply to the small intestine and colon from the superior mesenteric artery, branches of which include the middle, right, and ileocolic arteries as well as jejunal and ileal arteries and arterioles

Ischemia occurs secondary to hypoperfusion of an intestinal segment. When hypoperfusion is insidious in onset, collateral blood flow may develop, precluding or minimizing ischemia; however, the regions of the intestine with a solitary arterial supply, and the watershed areas, are both at increased risk of developing ischemia. The degree of intestinal injury is dependent on the duration and severity of ischemia. Acute or subacute mucosal sloughing and ulcerations occur as a result of ischemia. The loss of the mucosal barrier allows for bacterial translocation and toxin or cytokine absorption. Reperfusion injury can also occur if blood supply is re-established after a prolonged interruption. Segments of ischemic bowel that do not suffer acute necrosis or perforation can heal with stenosis or stricture as the long-term sequelae of bowel ischemia.

Thromboembolic events that lead to mesenteric ischemia usually involve the SMA instead of the other mesenteric arteries (IMA and celiac artery). This is because of the anatomic position of the SMA; the SMA is positioned vertically in relation to the aorta while the other vessels form more oblique angles with the aorta.

Classification

Intestinal ischemia can be classified into three broadly defined types:[1]

  • Acute mesenteric ischemia

    • Superior mesenteric artery embolus

    • Superior mesenteric artery thrombosis

    • Nonocclusive mesenteric ischemia

    • Superior mesenteric vein thrombosis

    • Focal segmental ischemia.

  • Chronic mesenteric ischemia.

  • Colonic ischemia

    • Reversible ischemic colonopathy

    • Transient ulcerating ischemic colitis

    • Chronic ulcerating ischemic colitis

    • Colonic stricture

    • Colonic gangrene

    • Fulminant universal ischemic colitis.

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