Overview

The mesentery is a fold of membrane that attaches the intestine to the wall around the stomach and intestines and holds it in place. Ischemia is lack of blood supply to a part of the body. 

Mesenteric ischemia is an inadequate blood flow to the small intestine. This decreased blood can cause ischemia, inflammatory injury, intestinal necrosis, and eventually patient death if untreated. It has high mortality rates ranging from 24% to 94%.²

Μesentric ischemia can be divided into acute and chronic types. Acute mesenteric ischaemia is often caused by a blood clot and requires immediate treatment, such as surgery. Chronic mesenteric ischaemia is usually caused by a buildup of fatty deposits in the arteries and is treated with open surgery or a procedure called angioplasty. Chronic mesenteric ischemia can develop into the acute form if left untreated.¹

Etiologies and risk factors of acute mesenteric ischemia

Acute Mesenteric Ischemia is divided into 4 types:

Arterial embolism

Arterial emboli are one of the most common causes of acute mesenteric ischemia. This group makes up around 40% to 50% of total cases. Most mesenteric clots begin in the heart. 

Most visceral arterial emboli mainly land in the superior mesenteric artery (SMA), due to the angle at which it is connected to the abdominal aorta. Whereas 15% of arterial emboli develop at the SMA's origin, 50% lodge distally near the point of origin of the middle colic artery, the SMA's first significant branch.³

Due to the underdeveloped collateral circulation, the onset of symptoms is typically rapid and is characterised by intense stomach discomfort that is sometimes accompanied by bloody diarrhoea. Based on the distribution of the ischemic bowel, the diagnosis of SMA embolism can often be made during surgery.³

Since most SMA emboli lodge distal to the beginning of the middle colic artery, letting the inferior pancreaticoduodenal branches to be perfused, the proximal jejunum is untouched, while the rest of the small intestine is ischemic.³

Risk factors include:

• Arrhythmia
• Myocardial infarction
• Rheumatic valve disease
• Endocarditis
• Cardiomyopathies
• Ventricular aneurysms
• History of embolic events
• Recent angiography³

Arterial thrombosis

Of all ischemic instances, 25% to 30% are caused by arterial thrombosis. The majority of mesenteric ischemia caused by arterial thrombosis happens in the context of severe atherosclerotic disease, and it usually happens close to the SMA's origin.³

Patients with this condition often have the capacity to endure significant blockage of the visceral arteries because atherosclerosis progresses slowly, allowing significant collateral vessels to form. When a major collateral artery or the last viable visceral artery blocks, bowel ischemia or infarction results. Bowel ischemia or infarction usually extends from the duodenum to the transverse colon, and its extent is usually larger than that of embolism.³

Between 70% and 100% of patients die around the time of surgery due in part to delayed diagnosis, severe intestinal ischemia-infarction, and the requirement for more complex surgical revascularisation.³

Risk factors include:

• Atherosclerosis
• Estrogen therapy
• Prolonged hypotension
• Hypercoagulability³

Mesenteric venous thrombosis

The least common cause of mesenteric ischemia is mesenteric venous thrombosis (MVT), making up for up to 10% of cases. Previously, the majority of cases were either classed as idiopathic or assumed to be related to other intra-abdominal pathologic diseases such as pancreatitis, intra-abdominal infection, or cancer. Since more instances are now linked to primary clotting problems, just 10% of cases are still classified as idiopathic, as a result of innovations in diagnostic procedures.³

Mesenteric venous thrombosis is often segmented, noted for gut wall oedema and haemorrhage, as well as localised mucosa sloughing. Thrombi start off in the venous arches and spread to include the curved channels. Hemorrhagic infarcts develop when intramural veins get blocked. The change from normal to ischemic gut occurs slower with venous embolism than with arterial embolism or thrombosis.

Death rates depend on the type of MVT (acute or chronic) and the extent of venous contribution. Long-term survival rates for people with acute MVT range from 30% to 40%, compared to at least 80% for those with chronic MVT.³

Risk factors include:

• Right-sided heart failure
• Previous deep vein thrombosis
• Hepatosplenomegaly
• Primary clotting disorder
• Malignancy
• Hepatitis
• Pancreatitis
• Recent abdominal surgery or infection
• Polycythemia
• Sickle cell disease³

Nonocclusive mesenteric ischemia (NOMI)

Nonocclusive disease affects about 20% of patients with mesenteric ischemia. Although the exact cause of nonocclusive mesenteric ischemia is unknown, widespread mesenteric vasoconstriction and a low cardiac output state are frequently linked.

The easiest way to recognise this condition from other types of AMI is through splanchnic vasoconstriction in response to hypovolemia, reduced cardiac output, low blood pressure, or vasopressors. The low-flow state that follows results in intestinal necrosis and hypoxia. Disseminated intravascular coagulation, damage from reperfusion, internal or external vasoconstrictors, and other factors might also be involved.

Digoxin is one of the vasoactive medications that has been linked to the cause of NOMI. Both in vitro and in vivo, digitalis preparations cause the smooth muscle of the splanchnic venous and arterial vasculature to contract.³

Patients undergoing enteral feeding in intensive care units who have had trauma or the stress of surgery have been reported to exhibit a rare form of nonocclusive ischemia. Among these patients, the reported incidence of AMI ranges from 0.3% to 8.5%.³

Risk factors include:

• Hypovolemia
• Hypotension
• Low cardiac output status
• Adrenergic agonists
• Digoxin
• Receptor blocking agents³

Etiologies and risk factors of chronic mesenteric ischemia

Chronic mesenteric ischemia frequently has multiple contributing factors. It can be either non-occlusive mesenteric ischaemia (NOMI), or occlusive mesenteric ischaemia. 

Occlusive chronic mesenteric ischaemia

Atherosclerosis, vasculitis, median arcuate ligament syndrome (MALS), or mesenteric venous thrombosis (MVT) can all result in occlusive chronic mesenteric ischaemia.⁴

1. Atherosclerosis

The most common cause of occlusive chronic mesenteric ischaemia is atherosclerosis, which is more common in women (65–72%). Although the exact predisposition of this female tendency is unknown, female patients should be made aware of it to prevent delays in receiving a diagnosis.⁴

2. Median arcuate ligament syndrome (MALS)

A rare cause of occlusive chronic mesenteric ischaemia is MALS. Although the exact prevalence of MALS is not known, 3.4% to 7.3% of asymptomatic people who undergo imaging for other purposes had the CA compressed by the MAL. MALS is more common in individuals with a low body mass index (BMI-30) and in young women (four females: one male).⁴

3. Vasculitis

One uncommon cause of occlusive chronic mesenteric ischaemia is vasculitis. Patients suffering from immunoglobulin (Ig)A vasculitis, polyarteritis nodosa, and Takayasu arteritis are most commonly observed to have mesenteric artery involvement and resulting chronic mesenteric ischaemia. Less often reported cases of mesenteric artery involvement include vasculitis linked to rheumatoid arthritis, vasculitis linked to anti-neutrophil cytoplasmic antibody (ANCA), Behcet's Disease, giant cell arteritis, and systemic lupus erythematosus.⁴

4. MVT

As venous collaterals typically form quickly, chronic mesenteric ischaemia due to MVT is uncommon. Nonetheless, patients with chronic MVT may also experience chronic mesenteric ischaemia.⁴

Non-occlusive chronic mesenteric ischaemia

Chronic (NOMI) is characterised by low-grade ischaemia and is linked to cardiac failure, pulmonary hypertension, severe chronic obstructive pulmonary disease, severe anaemia, mesenteric artery vasospasms, and low-flow states (dialysis patients with chronic kidney disease).

Risk factors include:

• Atherosclerosis
• Hypertension
• Diabetes mellitus
• Hypercholesterolemia
• Smoking
• Peripheral vascular disease
• Previous vascular surgery
• Coronary artery disease^4,5

FAQs

What is the main cause of mesenteric ischemia?

Mesenteric ischemia is an inadequate blood flow to the small intestine. Decreased blood can cause ischemia, inflammatory injury, intestinal necrosis, and eventually patient death if untreated.

What are some common risk factors for acute mesenteric ischemia?

Some of the common risk factors include myocardial infarction, rheumatic valve disease, endocarditis, cardiomyopathies, ventricular aneurysms, history of embolic events, recent angiography, atherosclerosis, prolonged hypotension, hypercoagulability, previous deep vein thrombosis, malignancy, primary clotting disorder, hepatitis, pancreatitis, recent abdominal surgery or infection, low cardiac output status, digoxin, smoking, hypertension, diabetes mellitus, and hypercholesterolemia.

What are the 4 types of acute mesenteric ischemia?

The 4 types of acute mesenteric ischemia are arterial embolism, arterial thrombosis, mesenteric vein thrombosis, and non-occlusive ischemia.

What is the difference between acute mesenteric ischemia and chronic mesenteric ischemia?

The acute type is often caused by a blood clot and requires immediate treatment, such as surgery. The chronic type is usually caused by a buildup of fatty deposits in the arteries and is treated with open surgery or a procedure called angioplasty.

Summary

Mesenteric ischemia collectively is an inadequate blood flow to the small intestine. This decreased blood can cause ischemia, inflammatory injury, intestinal necrosis, and eventually patient death if untreated. It has high mortality rates ranging from 24% to 94%. Μesentric ischemia can be divided into acute and chronic types. Chronic mesenteric ischemia develops into acute form if left untreated.

Mesenteric ischemia is further divided into arterial embolism, arterial thrombosis, mesenteric vein thrombosis, and non-occlusive ischemia. However arterial embolism remains the most common cause of mesenteric ischemia.