Mesenteric ischemia refers to ischemia of small intestine, whereas colonic ischemia refers to ischemia of large intestine. Bowel ischemia can be acute or chronic, depending upon how quickly the occlusion of vessels of intestine occurs. In acute ischemia, there is sudden occlusion of a blood vessel supplying the intestine. It is mostly embolic or thrombotic in nature and requires immediate surgery. In contrast, chronic mesenteric ischemia occurs when there is slow narrowing of blood vessels supplying the intestine, giving sufficient time for collateral circulation to develop, preventing intestinal necrosis.

Mesenteric ischemia refers to ischemia of small intestine, whereas colonic ischemia refers to ischemia of large intestine. Bowel ischemia can be acute or chronic, depending upon how quickly the occlusion of vessels of intestine occurs. In acute ischemia, there is sudden occlusion of a blood vessel supplying the intestine. It is mostly embolic or thrombotic in nature and requires immediate surgery. In contrast, chronic mesenteric ischemia occurs when there is slow narrowing of blood vessels supplying the intestine, giving sufficient time for collateral circulation to develop, preventing intestinal necrosis.

Mesenteric blood supply:

There are 3 vessels which supply the intestine:

1. Coeliac artery
2. Superior mesenteric artery
3. Inferior mesenteric artery

There is rich collateral circulation between these vessels (Figure 2) so that chronic stenosis of one vessel is tolerated well. Ischemia occurs when at least two vessels are showing critical stenosis.

                                                                          Figure 1: Chart showing the etiology of mesenteric ischemia

                                                                        Figure 2: Collateral circulation between the three mesenteric vessels

ChronicMesenteric ischemia:

Chronic mesenteric ischemia (CMI) mostly caused by atherosclerotic narrowing of the two or more vessels supplying the gut[1,2]

Causes of CMI include:

• Atherosclerosis involving the proximal portions of the celiac, superior mesenteric, or inferior mesenteric artery.
• Dissection
• Vasculitis, especially Takayasu disease
• Fibromuscular dysplasia
• Radiation
• Cocaine abuse

One rare cause is celiac artery compression syndrome, also known as median arcuate ligament syndrome, in which intestinal ischemia is caused by compression of celiac trunk by median arcuate ligament[3]. 

CMI is a rare diagnosis.  Moawad and Gewertz could find only 330 cases in search of 20 years literature1. Because many cases remain undiagnosed, the true prevalence may not really be low.

Since most of the cases are due to atherosclerosis, risk factors include diabetes, smoking, hypertension, older age, dyslipidemia and coronary artery disease.

Symptoms of CMI

Classical triad of symptoms are 1. Post prandial abdominal pain 2. Fear to eat due to anticipation of severe pain(Sitophobia)  3. Weight loss

Abdominal pain typical occurs within 10-60 minutes of food intake and may be so severe that patient fears to eat. Other symptoms include nausea, vomiting and diarrhoea.

Most of the times, diagnosis is delayed, as the disease is not suspected. Patient might have undergone ultrasound, upper and lower gastro intestinal (GI) endoscopy and many times CT coronary angio or conventional coronary angiography with possibility of post myocardial infarction (MI) angina.

Work up:

• History:  High index of suspicion should be kept
• Imaging:

Duplex Ultrasound :  Fasting duplex criteria for mesenteric stenosis(>70%)[4]

SMA:   Peak systolic velocity of 275 cm/s or greater

Celiac artery : Peak systolic velocity of 200 cm/s or greater CMI.

CT angiography: Has sensitivity of 96% and specificity of 94% for detecting CMI[5]. It is mainly important to detect vascular disease in celiac trunk and SMA[6]. Schaefer et al found it to be the best modality in comparison to MR angiography and duplex ultrasound7.

Magnetic Resonance Imaging/MRA: Advantage - ability to image without radiation. It has been found to accurately imagine mesenteric vessels[8,9].

Disadvantage:  potential inability to accurately evaluate the IMA.

It is not considered initial investigation of choice in emergency settings[10,11].

Catheter angiography:  Gold standard for diagnosing mesenteric vascular disease. Angiography can be done to confirm the diagnosis before surgery or endovascular therapy is planned.

Management:  Once symptoms of mesenteric ischemia are there, revascularization is required. Open surgical repair was standard care of treatment in CMI, but at present initial approach is endovascular repair( Figures 3-5) in around 80% of patients[12]. It is minimally invasive, has high initial success rate and has few complications13. However, plain balloon angioplasty has lower success rate and high rate of restenosis, stent is almost always implanted[13,14]. Restenosis can still occur in around 40% patients and 20% may require repeat intervention[15,16]. Also, the results of angioplasty may depend upon the vessel revascularized. In a study, primary patency was better in SMA group than in coeliac artery group17.

Open surgical repair has significant post operative complications and small increase in mortality at 30 days, compared to angioplasty. However it has better long term results and low risk of  recurrence at 3 years[18].

Figure 3: Tight stenosis of SMA, in a patient of CMI, missed for 8 years, in many hospitals. Upper and lower GI endoscopy, ultrasound of abdomen, coronary angiography were normal. Weight loss of 14 Kg in last two months.

                                                                                             Figure 4: Implantation of stent in same patient of CMI.

                                                    Figure 5: Wide open SMA after stenting. All symptoms disappeared. Weight gain of 4 kg in two weeks.

Acute mesenteric ischemia (AMI):  It can be due to acute arterial occlusion (AAO) or mesenteric venous occlusion (MVO) or non occlusive mesenteric ischemia (NOMI). Acute mesenteric arterial ischemia (AMAI) is an surgical emergency. It is caused by embolic occlusion in 40-50

Mesenteric ischemia van be chronic or acute. CMI is difficult to diagnose as patient has varied presentation. High index of suspicion is must. Patient with post prandial abdominal pain with all routine investigations inconclusive, and significant weight loss should be investgated for CMI. AMI is an emergency, and could be due to acute mesenteric artery occlusion, NOMI or due to MVT. Here also high risk of suspicion is required. In suspected cases, early CT angio or MRA should be done. Delay in diagnosis is important cause of mortality.