Intestinal Ischemia

Intestinal ischemia can be broadly categorized as either mesenteric (small-bowel) ischemia or colonic ischemia and can present as acute or chronic disease. Patients often have underlying conditions (e.g., atrial fibrillation or vasculitis) that predispose them to the formation of blood clots (thrombosis).

The cardinal sign of intestinal ischemia is abdominal pain. Although intestinal ischemia is largely considered a rare cause of abdominal pain, delayed diagnosis can be associated with significant morbidity and mortality.

Acute Mesenteric Ischemia

Types and Causes

• acute mesenteric arterial embolism, usually from a cardiac source

  • risk factors: atrial fibrillation, recent myocardial infarction (MI) or cardiac thrombi, mitral-valve disease, left ventricular aneurysm, endocarditis, and previous embolic disease

  • presentation: sudden, severe abdominal pain with or without vomiting

  • most common involved vessels: superior mesenteric artery (SMA) and its branches

• acute mesenteric arterial thrombosis, generally in the presence of preexisting atherosclerotic disease

  • risk factors: diffuse atherosclerotic disease, postprandial pain, weight loss

  • presentation: progressive or sudden abdominal pain, vomiting, diarrhea, and/or melena

  • most common involved vessels: celiac trunk, SMA, inferior mesenteric artery (IMA)

• nonocclusive mesenteric ischemia (NOMI), usually from underlying atherosclerosis and acute low-flow state (e.g., systemic hypotension)

  • risk factors: cardiac failure, low-flow states, multiorgan failure, vasopressors, abdominal compartment syndrome

  • presentation: progressive, mild pain

  • most common involved vessels: SMA vasoconstriction or mesenteric venous thrombosis, either idiopathic or secondary to an intra-abdominal process

  • risk factors: portal hypertension, history of venous thromboembolism (VTE), oral contraception, estrogen use, thrombophilia, and pancreatitis

  • presentation: usually nonspecific gastrointestinal (GI) symptoms

  • most common involved vessels: superior mesenteric vein

Evaluation and Diagnosis

Mesenteric ischemia can be difficult to diagnose because of the rare incidence and nonspecific symptoms. Therefore, diagnosis requires a high index of suspicion.

• Clinical features: The hallmark of early presentation is abdominal pain out of proportion to physical exam. In addition, patients with chronic mesenteric ischemia can present with other nonspecific GI symptoms, such as postprandial pain, nausea, vomiting, weight loss related to food avoidance, or change in bowel habits.

• Laboratory studies: Although laboratory studies are nonspecific, lactic acidosis, leukocytosis, and an elevated D-dimer level may be seen in patients with suspected mesenteric ischemia.

• Diagnostic imaging: Definitive diagnostic tests should be initiated immediately in patients with suspected mesenteric ischemia and risk factors (e.g., atherosclerosis, atrial fibrillation). Imaging options include:

  • Computed tomography angiography (CTA) is the diagnostic study of choice.

  • Magnetic resonance angiography (MRA) can be performed if CTA is not possible (e.g., secondary to contrast allergy or renal failure) but is limited by length of exam.

  • Mesenteric angiography is the gold standard but has been replaced largely by CTA. Although invasive, it can be therapeutic if a lesion is found that is amenable to intervention.

(Source: Mesenteric Ischemia. N Engl J Med 2016.)

Treatment

Initial treatment: The focus of initial treatment is fluid resuscitation and monitoring of electrolytes because infarction can progress quickly to acidosis, hyperkalemia, and sepsis associated with a systemic inflammatory response.

• Immediate initiation of broad-spectrum antibiotics is recommended due to the high risk of infection associated with acute mesenteric ischemia.

• Anticoagulation with heparin infusion should also be initiated as soon as possible once a diagnosis is made.

Definitive treatment: Once a diagnosis is made, definitive treatment involves a range of interventions, including endovascular or surgical repair.

• In patients with overt peritonitis, laparoscopy/laparotomy is recommended.

• In cases that require vascular reconstruction or where there is suspicion of intestinal ischemia, open surgery is required, generally with a “second look” surgery within 48 hours to assess the viability of the bowel after revascularization.

  • Patients who undergo revascularization are recommended to be placed on anticoagulation for at least 6 months or possibly lifelong if there is underlying hypercoagulability.

Colonic Ischemia

Causes

Colonic ischemia is the most frequent form of intestinal ischemia, and in contrast with mesenteric ischemia, generally results from nonocclusive causes such as small-vessel disease, systemic hypotension, decreased cardiac output, or aortic surgery. However, a specific inciting factor cannot be identified in most patients.

Evaluation and Diagnosis

Evaluation and diagnosis of colonic ischemia is similar to that of mesenteric ischemia except that large-vessel thrombus or embolus are seldom the cause of colonic ischemia.

• Clinical features: Clinically, patients present with mild, cramping abdominal pain (typically left lower quadrant), fecal urgency, and bloody bowel movements. In patients with typical clinical features, risk factors that should raise suspicion for colonic ischemia include cardiovascular disease, diabetes, and prior aortic surgery.

• Diagnostic imaging: Abdominal and pelvic CT scan with intravenous (IV) and oral contrast is the initial investigation of choice, followed by colonoscopy if needed for confirmation of the diagnosis.

  • Suggestive findings include bowel-wall thickening/edema, thumbprinting, or pneumatosis or porto-mesenteric venous gas in patients with transmural infarction.

  • If acute mesenteric ischemia cannot be excluded in the patient, CTA is the test of choice.

  • Colonoscopy should not be performed in patients who have signs of peritonitis or pneumatosis on imaging.

Management

Most cases resolve spontaneously and thus treatment is generally supportive, with aggressive hydration, bowel rest, and occasionally antibiotics in moderate or severe disease due to risk for infection. Surgery is reserved for peritonitis, fulminant colitis, persistent hypotension, pneumatosis intestinalis on imaging, or massive bleeding.