Mesenteric ischemia is a manifestation of peripheral vascular disease in which the blood supply fails to meet the metabolic demands of visceral organs. Acutely, it is a surgical emergency resulting in severe abdominal pain classically described as "pain out of proportion to physical examination." However, chronic mesenteric ischemia (CMI) often presents with vague abdominal pain that may be difficult to differentiate from other, more common causes of abdominal pain.
Factors that predispose the mesenteric vessels to atherosclerosis include the following:
When the arterial lumen narrows secondary to atherosclerosis, any demand in blood supply that occurs during eating can result in severe abdominal pain and even mesenteric ischemia.
Mesenteric artery stenosis is relatively common, occurring in up to 10% of the population over 65 years of age. However, CMI has a very low incidence, accounting for less than 1 in 1000 hospital admissions for abdominal pain. Patients are typically between the ages of 50 and 70 years of age, with a strong female predominance, and have other coexisting manifestations of atherosclerotic disease.
The mesenteric circulation consists of three primary vessels that supply blood to the small and large bowel: the celiac artery, superior mesenteric artery (SMA), and inferior mesenteric artery (IMA). Blood flow through these arteries increases within an hour after eating due to an increase in metabolic demand of the intestinal mucosa. Diffuse atherosclerosis, usually occurring at the origin of these vessels, is the primary mechanism and accounts for 95% of CMI. Chronic occlusion of a single vessel allows collateral blood flow to compensate, thus symptoms do not typically present until at least two primary vessels are occluded. Less common causes include vasculitis, fibromuscular dysplasia, and radiation.
The bowel that is excised at surgery will usually reveal diffuse atherosclerosis in the mesenteric vessels. There is usually atrophy of the villi, which leads to loss of absorptive surface.
Patients typically present with “intestinal angina.” Postprandial abdominal pain occurring within 15 to 30 minutes and lasting up to 4 hours that is associated with a fear of eating, ultimately results in weight loss. Additional nonspecific symptoms include nausea, vomiting, early satiety, diarrhea, or constipation. The majority of patients will have a history of symptoms related to diffuse atherosclerotic disease, such as angina, transient ischemic attacks/cerebrovascular accidents, or lower extremity claudication. Physical exam may reveal diffuse mild abdominal tenderness without rebound or guarding, but is more often normal. An abdominal bruit may be audible in up to 50% of patients, but is neither specific nor sensitive.
Most patients undergo an extensive gastrointestinal (GI) disease workup for more common causes of postprandial abdominal pain and weight loss, such as peptic ulcers, cholecystitis, and malignancy, which delays the diagnosis of CMI. Demonstrating the stenosis or occlusion of the primary mesenteric vessels via vascular imaging is required for the diagnosis of CMI. CT angiography (CTA) is the preferred initial, non-invasive modality, as it identifies or excludes atherosclerotic stenosis of the mesenteric vessels while simultaneously ruling out other abdominal etiologies. In the outpatient setting, duplex ultrasonography is a reasonable screening modality, with peak systolic velocities greater than 275 cm/second and 200 cm/second indicating greater than 70% stenosis of the spinal muscular artery and celiac artery, respectively. Arterial digital subtracted angiography (DSA) is the gold standard for confirming the diagnosis of CMI if the results of noninvasive imaging are equivocal, and it is used to plan therapeutic interventions.
Asymptomatic patients with CMI are managed conservatively, with smoking cessation and antiplatelet therapy. These patients have a five-year mortality of 40%, with the majority of deaths attributed to myocardial infarction or cardiovascular death. Symptomatic CMI is an indication for either open or endovascular revascularization, as patients with untreated symptomatic CMI carry a five-year mortality rate that approaches 100%.
Indications for Surgery
Signs of peritonitis on physical exam
Massive lower GI hemorrhage
Ongoing signs of abdominal pain, fever, or sepsis
Symptoms that have persisted for more than 14 to 21 days
Chronic malabsorption leading to protein-losing colopathy
Colonoscopic evidence of segmental colitis with frank ulceration
Presence of an ischemic stricture and abdominal symptoms
Open revascularization is accomplished via antegrade inflow (aortomesenteric or aortoceliac bypass) or retrograde inflow (from the iliac artery), with either a vein or prosthetic conduit. Endovascular revascularization has surpassed open revascularization as the preferred initial treatment as it is minimally invasive with few perioperative complications. The occluded vessels are accessed via the femoral artery, and blood flow is reconstituted by balloon angioplasty followed by stent placement.
Nutritional status is an important preoperative assessment as patients are often malnourished at the time of diagnosis; total parenteral nutrition may be necessary both pre- and postoperatively. The optimal revascularization approach depends heavily on the anatomy and preoperative condition of the patient.
Because these patients have diffuse atherosclerosis, they are prone to myocardial infarction during and after surgery. Thus, prior to any elective surgery, the patient must be well hydrated and the medical condition optimized. Recovery is best done in the intensive care unit.
A very common complication in the postsurgical period is renal failure, which can be permanent. Thus, the patient must be seen by the nephrologist prior to surgery. Hydration is the key to preventing renal dysfunction.
Chronic mesenteric ischemia can lead to the following complications:
Poor quality of life
Avoidance of food and malnutrition
Thrombosis leading to ischemia of the colon
Repeated hospital admissions
GI tract bleeding
For most patients with chronic mesenteric ischemia, the quality of life is poor. The constant fear of abdominal pain that may occur when eating food leads to significant weight loss. The malnourished state often leads to other metabolic and endocrine problems, bone thinning and easy bruising.
While endovascular revascularization is associated with shorter hospital stays and fewer serious complication rates, it also is associated with lower long-term patency rates and a shorter time to the return of symptoms when compared to open surgical revascularization. Restenosis occurs in up to 40% of patients, many of whom will require reintervention.
Postprandial pain also is associated with biliary disease, peptic ulcer disease, pancreatitis, diverticulitis, gastric reflux, irritable bowel syndrome, and gastroparesis. Malignancy must be ruled out in an older patient presenting with GI symptoms and weight loss.