What Is a Mesenteric Artery Ultrasound?
Ultrasound of the mesenteric artery/arteries is used to demonstrate disease that impacts the health and survival of the intestines and portions of the stomach. The arterial supply to the intestines consists of:
- The superior mesenteric artery (SMA)
- The inferior mesenteric artery (IMA)
Both of these are branches off the descending abdominal aorta. Because the collateral circulation to the organs supplied is not briskly confluent and therefore only functions for transient periods of inadequate perfusion, prolonged hypoperfusion due to mesenteric artery disease can risk devastating ischemia and tissue death over time. The arterial supply at the splenic flexure and the rectosigmoid junction are particularly susceptible areas.
The Superior Mesenteric Artery
The superior mesenteric artery, via its branches, supplies blood perfusion to the pancreas, a portion of the stomach, the small intestines (duodenum, jejunum, and ileum), and portions of the large bowel.
The Inferior Mesenteric Artery
The inferior mesenteric artery, via its branches, supplies blood to the transverse, descending, and sigmoid colon and the rectum.
Mesenteric Artery Ultrasound
Ultrasound of the mesenteric arteries is used to identify stenosis, plaque, or embolic occlusions that can interrupt the blood supply to the entire intestinal system, spleen, and portions of the liver and stomach. Duplex ultrasound, a combination of:
- B (brightness) mode: Renders an image based on the differences of tissue density reflected back and of
- Doppler ultrasound technology: Which reflects high frequency sound waves off of red blood cells to discern motion and blood flow is useful to identify arterial stenosis or occlusion in the superior mesenteric artery from atherosclerosis or arterial thromboembolic disease.
- CT and MRI imaging: Used to confirm the diagnosis of acute mesenteric ischemia. Contrast is generally not used in these advanced imaging protocols, due to its tendency to obscure mesenteric vessels and bowel wall integrity, which can delay the diagnosis. Such a diagnosis is a true life-threatening emergency for which any delay can create unnecessary mortality. Of CT and MRI, CT is preferred due to its ready availability in most settings and its speed of rendering results where speed is a priority.
- Direct imaging: Is done via endoscopic colonoscopy or rectosigmoidoscopy to confirm a diagnosis of ischemic colitis.
Diagnosis of a Mesenteric Artery Ultrasound
Disorders of the mesenteric arterial blood supply to the intestines can present either chronically or acutely.
- Chronic presentations from mesenteric arterial atherosclerosis and stenosis present with abdominal pain and bowel dysfunction. Since atherosclerosis is a progressive disease, so are the symptoms.
- Acute presentations from thromboembolism that suddenly occludes the arterial blood supply to the intestinal tract will typically manifest as sudden, severe abdominal pain and cramping, bloody diarrhea, and when necrosis is present, high fever.
Types of Testing That Can Be Preformed.
- Blood Tests: Blood tests provide only non-specific results and can even be normal with intestinal ischemia. Because of the urgency in establishing a diagnosis for mesenteric disease resulting in intestinal ischemia, waiting for the results of blood tests is ill-advised. Once results do come in, however, elevations in serum lactate and serum amylase levels are often present.
- X-rays: Plain abdominal radiography is not very helpful and can be completely normal in 25% of patients with mesenteric ischemia. Positive findings that can be seen include distended loops of bowel, bowel wall thickening, or even free air in the abdomen from a rupture of a portion of necrotic bowel. Any rupture is a surgical emergency.
- Duplex Ultrasound: B (brightness) mode and Doppler ultrasonography can help identify arterial stenosis in chronic disease or occlusion of the superior mesenteric artery in acute situations, and when such conditions are suspected, confirmation is made via CT without contrast and/or rectosigmoidoscopy to rule out bowel ischemia and necrosis.
- CT: CT imaging is preferred to MRI, since it is quicker, less expensive, and readily available in most facilities. Contrast is typically not used because it interferes with visualizing some details, such as bowel wall integrity.
Tests to Exclude Other Conditions
The clinical presentation typical of bowel ischemia and/or necrosis can be similar to other conditions, such as Clostridium difficile colitis, and stool examination is part of the investigation of any serious intestinal conditions. Enzyme immunoassays, cell cultures, anaerobic cultures, and nucleic acid amplification testing are used to rule out this serious infection whose signs and symptoms can mimic bowel ischemia.
Medical Management of Mesenteric Artery Disease
Management of mesenteric artery disease can be either conservative or emergent, depending on the severity or presentation. For patients who are stable and have clinical signs of bowel ischemia, close surveillance while on anticoagulation (heparin) is quite feasible. As the urgency and severity increase, the options become more aggressive and invasive. Diagnostic imaging, from duplex Doppler ultrasound to CT imaging is used for close surveillance of a condition that can become dangerous very quickly.
Surgical Management of Mesenteric Artery Disease
For those who have no risk factors against tolerating surgery, immediate abdominal surgery (laparotomy) is indicated when there is an exacerbation that involves peritonitis or bowel rupture. The ideal sequence of therapeutic events would be endovascular revascularization prior to any surgery so that any bowel resection could be minimized, but this is often unfeasible.
Open surgical embolectomy is the traditional treatment for acute embolism along with any necessary clearing of thrombus that could provide a site for further embolic development. Open surgery, besides being directly therapeutic, allows the most accurate assessment of bowel wall integrity via direct visualization.
For mesenteric artery thrombosis, mesenteric artery bypass is performed, because merely removing the thrombus is unlikely to remove the thrombogenic atherosclerotic plaques and future embolization’s.
Via invasive radiological techniques, an endovascular access through the femoral or brachial artery can be used to suction out the clot; alternately, thrombolytic therapy can be delivered to the thrombus through a catheter. Endovascular thrombectomy can be performed mechanically or balloon angioplasty and stenting can be accomplished without the increased morbidity an abdominal surgery would have. Some vascular specialists prefer this approach over open surgery, due to evidence it may be as effective as the open surgical approach, while others prefer open surgery so that there can be direct and immediate inspection of the bowel and any necessary resection can be performed in a timely fashion.
Mesenteric Artery Ultrasound and Prevention
Ultrasound of the superior mesenteric artery is used to diagnose stenosis, thrombosis, and emboli. In a stable patient, this can be used in conjunction with confirmation via CT imaging to plan a protocol of close surveillance and/or conservative endovascular management to prevent embolization and bowel ischemia.
Chronic disease in stable patients can allow prevention of bowel ischemia or necrosis via all of the therapeutic tools used in preventing complications from any atherosclerotic disease process:
- Control of hypertension with antihypertensive medications(s)
- Management of dyslipidemia (high cholesterol/triglyceride) with statin drugs
- Strict glycemic control in diabetics, including maintenance of a target glycated hemoglobin A1c
- Smoking cessation
- Diet and nutrition consultation
- Physical exercise
- Weight management
- Specific to mesenteric artery atherosclerosis, prevention of ischemic sequelae includes
- Close surveillance via mesenteric artery ultrasound and confirmatory CT imaging
- Revascularization via endovascular balloon angioplasty or mechanical thrombectomy
- Pre-emptive elimination of thrombus via mesenteric artery by-pass surgery
- In acute situations, prevention of sepsis and death is realized via emergency surgery and bowel resection
Mesenteric artery stenosis is a serious risk to organs that do not have a generous, forgiving collateral circulation, and patients with such a diagnosis benefit from strategies to prevent serious, life-threatening consequences.