Mesenteric artery thrombosis refers to the formation of a blood clot within the superior or inferior mesenteric artery. This condition does not only increase the overall risk for thromboembolism but may also lead to mesenteric ischemia and acute mesenteric artery occlusion, diseases associated with high morbidity and mortality.
There are no pathognomonic symptoms for MAT. Poorly localized abdominal pain is most commonly observed, and in cases of considerable reduction of blood supply to the intestines, it may be very intense. The patient's medical history is of major importance to orient the physician towards a possible source of pain and because atherosclerosis is the main cause of MAT, affected individuals often have a history of hypertension, hypercholesterolemia or diabetes mellitus. Some patients may have a history of myocardial infarction or stroke. Most MAT patients smoke; they may be overweight or obese. Chronic MAT may be associated with intermittent, moderate abdominal pain that aggravates after meals. Patients may complain of diarrhea and weight loss.
As has been indicated above, major complications of MAT are acute mesenteric ischemia and mesenteric artery occlusion - and these do cause severe abdominal pain but both may also be provoked by other pathologies. In fact, they are generally diagnosed in patients suffering from aortic dissection and aortic aneurysm. Moreover, pathologies like pancreatitis or cholecystitis may evoke a similar clinical picture dominated by acute onset abdominal pain . All these diseases may require urgent laparotomy and thus, it may not be possible to obtain a complete workup before deciding about a surgical intervention. Here, it is more important to realize that the patient will probably die without emergency surgery.
Diagnostic imaging is the basis of MAT workup. Reduction of intestinal blood supply can be visualized in a very sensitive and specific manner in cases of near or complete artery occlusion. In contrast, the appearance of mesenteric ischemia itself is rather challenging.
Spiral computed tomography with contrast enhancement in arterial and venous phases is the method of choice to confirm suspected MAT ; administration of intravenous contrast may enhance the sensitivity of the examination, but is less frequently used. Computed tomography scans allow for the visualization of both mesenteric arteries, blood flow through individual branches and existing collaterals that still supply affected parts of the intestines.
Besides vascular anomalies, pathological alterations of the intestinal wall may indicate ischemia or necrosis. Gas within the bowel wall indicates bacterial proliferation and implies mucosal necrosis. If deeper layers are affected, gas will also become visible in the portal vein.
Magnetic resonance imaging may constitute an alternative option that can yield similar findings.
Laboratory analyses of blood samples should be obtained to assess the overall condition of the patient, but will not yield any findings that point at an underlying MAT. Metabolic acidosis and leukocytosis are frequent findings.
If MAT is diagnosed during early stages of the disease, intra-arterial thrombolysis is indicated. This is an effective technique and patients receiving such treatment rarely require subsequent laparotomy and bowel resection. One might expect hemorrhages to complicate the application of thrombolytics, but experience shows that bleeding occurring during the procedure is minimal and self-limiting. In order to carry out intra-arterial thrombolysis, drugs like heparin, streptokinase, urokinase or alteplase are injected percutaneously into the affected vessel. Intra-arterial thrombolysis may be combined with thrombus aspiration .
Thrombolytics need to be stopped (and heparin action has to be reversed by application of protamine) before surgery can be initiated . Therefore, patients who are diagnosed with an acute surgical abdomen, should not receive heparin or fibrinolytics. Here, thrombectomy with or without simultaneous bowel resection has to be performed.
While MAT itself may have a doubtful prognosis, it is rarely diagnosed before mesenteric ischemia or mesenteric artery occlusion occurs and these pathologies are associated with poor outcomes.
According to a retrospective study conducted in Sweden, 26% of patients admitted for acute occlusion of the superior mesenteric artery died prior to being discharged from the hospital. About 40% of all patients died within a year, but their average age of 78 years has to be considered when interpreting this number . In another study, two out of three patients who underwent surgery because of acute mesenteric ischemia died within the perioperative period .
Thrombi may form within the mesenteric artery either due to endothelial lesions affecting that vessel or because of systemic diseases leading to hypercoagulability.
By far the most common cause of MAT is the presence of atherosclerotic plaques within that artery. Atherosclerotic plaques consist of lipid-laden macrophages that may eventually turn into foam cells, or extracellular lipid deposits and minor quantities of immune cells . They interfere considerably with endothelial function and thus facilitate coagulation. Moreover, atherosclerotic plaques constitute a mechanical obstruction and provoke local blood stasis - a condition that also favors thrombosis. Diseases like hypertension, hypercholesterolemia, diabetes mellitus as well as obesity increase the risk of atherosclerosis and thus of MAT.
Contrary to aortic dissection and aortic aneurysm, mesenteric artery dissection,and mesenteric artery aneurysm are rare events  . In both conditions, endothelial lesions and disturbances of blood flow increase the risk of MAT.
Any other pathology leading to mesenteric artery endothelial damage may also cause MAT. This applies to inflammatory, neoplastic and traumatic injury of the vessel. Cases of giant cell arteritis and Takayasu arteritis involving the mesenteric artery have been reported . MAT has also been related to gastrointestinal neoplasms and therapy of such malignancies.
A variety of systemic disorders is related to hypercoagulability. Dehydration, thrombophilia, polycythemia, antithrombin III, protein C and S deficiencies and disseminated intravascular coagulation are mentioned as examples. Here, thrombi formation may occur in any blood vessel including but not limited to the mesenteric artery. Of note, pregnancy and intake of oral contraceptives make a patient similarly susceptible to thrombosis.
Epidemiology of MAT largely equals that of its main underlying disease, i.e., atherosclerosis. This disease is frequently diagnosed in patients suffering from hypertension, hypercholesterolemia or diabetes mellitus, and most affected individuals are older than 70 years. In fact, two retrospective studies regarding mortality due to mesenteric ischemia and mesenteric artery occlusion were conducted on patient cohorts with a mean age of 72 and 78 years, respectively  . However, young adults may also be affected.
There is not one but two mesenteric arteries: the superior mesenteric artery and the inferior mesenteric artery. Both originate from the abdominal aorta, but while the former supplies the pancreas and large parts of small and large intestines (duodenum, jejunum, ileum as well as ascending and transverse colon), the latter delivers blood to the descending colon, sigmoid colon, and rectum. MAT almost exclusively affects the superior mesenteric artery, but systemic diseases may also provoke the formation of blood clots within the inferior mesenteric artery. Predisposing conditions like dissection and aneurysm have also been described in the latter.
Pathophysiological events arising from either type of MAT are similar but differ in terms of the segment of the gastrointestinal tract affected. If blood clots in these arteries are sufficiently large, they will interfere with blood supply to the intestines. Of note, small thrombi may not cause any clinical symptoms, but they may grow and eventually lead to enteric ischemia or infarction.
The intestinal wall consists of mucosa, submucosa, smooth musculature and serosa or adventitia. All depend on oxygen and nutrient supply, but oxygen consumption by the mucosal epithelium is the largest. In a case of ischemia, the primary goal is to maintain bowel integrity, and therefore, the outer layers of the intestinal wall will preferentially be supplied with blood. This phenomenon is known as shunting and causes severe mucosal lesions after as little as 60 minutes of mesenteric ischemia . However, abdominal pain is often the only symptom during initial stages of the disease. Because of frequent delays in diagnosis, mesenteric ischemia has a poor prognosis .
If mesenteric artery occlusion occurs, ischemia will immediately affect the outer layers of the intestinal wall, too, and cause transmural infarction, necrosis, and perforation. This condition rapidly leads to bacterial translocation, peritonitis, sepsis, and death.
Prevention of MAT basically consists of preventing atherosclerosis. Hypertension, hypercholesterolemia, diabetes mellitus, obesity and tobacco consumption are well -known risk factors for atherosclerosis and consequently, blood pressure, serum lipid,and glucose levels, as well as body weight, should be maintained within a healthy range. Smokers should be advised to discontinue the habit.
In the case of permanent hypercoagulability, long-term administration of anticoagulants may be required to avoid thrombi formation in the mesenteric arteries and other vessels.
Large parts of the gastrointestinal tract, namely duodenum, jejunum, ileum, colon, and rectum, depend on mesenteric artery blood supply. Consequently, any interference with the blood flow through the respective vessels may cause ischemic lesions in those organs. An important risk factor for mesenteric ischemia is mesenteric artery thrombosis (MAT), i.e., the formation of a blood clot within the superior or inferior mesenteric artery.
Small thrombi within the mesenteric artery may not directly lead to mesenteric ischemia or mesenteric artery occlusion, but they pose a double threat for severe complications. On the one hand, local disturbances of fluid mechanics caused by microthrombi facilitate thrombus growth, and bigger thrombi may significantly diminish blood supply to the intestines. On the other hand, microthrombi are usually not firmly attached to the arterial wall, they can be easily carried away and may provoke cerebral, myocardial or renal infarction.
Common triggers of coagulation are endothelial damage, blood stasis or pathologies that disturb the equilibrium between pro- and anticoagulatory factors. Such conditions may be limited to the mesenteric artery or affect the whole cardiovascular system. In fact, the most common cause of MAT is atherosclerosis, an entity that is also related to aortic thrombosis and blood clot formation within other arteries. Since atherosclerosis is typically a disease of the elderly, MAT is most commonly diagnosed in patients pertaining to that age group.
Diagnosis is often delayed until severe complications arise and unfortunately, morbidity and mortality increase with thrombus size and the extent of intestinal ischemia. Thrombolysis is the most effective treatment for MAT and its consequences, but irreversible bowel damage may nevertheless lead to bacterial translocation, peritonitis, septic shock,and death. Thus, even though complete thrombolysis can be achieved, intestinal viability needs to be closely monitored. Bowel resection may be unavoidable in certain cases .
Small and large intestines mainly depend on blood supply provided by the superior and inferior mesenteric arteries. The former delivers oxygen and nutrients to the small intestines and the proximal parts of the colon, the latter to the distal parts of the colon and the rectum.
Similar to other parts of the cardiovascular system, blood clots may form within these arteries. Here, this process is called mesenteric artery thrombosis (MAT).
The main cause of MAT is atherosclerosis, i.e., the formation of atherosclerotic plaques in the arterial wall. Patients who suffer from hypertension, hypercholesterolemia or diabetes mellitus have increased risks of atherosclerosis and thus of MAT. This also applies to overweight or obese people and smokers.
Thrombi may significantly diminish blood flow to the gastrointestinal tract. In some cases, this may cause mesenteric ischemia; if the vessel is completely blocked, the patient will sustain acute mesenteric artery occlusion. Although both complications follow distinct temporal patterns, the two of them are associated with severe damage to the intestinal wall. If bowel integrity cannot be preserved, bacteria translocate into the abdominal cavity, cause peritonitis, septic shock, and death.
The most common symptom of MAT is abdominal pain, poorly localized and potentially very intense. Additional symptoms may not manifest until very late stages of the disease.
Any delay in treatment worsens the patient's prognosis. Consequently, the decision for abdominal surgery may be taken although a clear diagnosis has not yet been made. The patient's medical history, the acute onset of severe abdominal pain and suspicious findings in diagnostic imaging may suffice to prepare a surgical intervention.
Diagnostic imaging, namely computed tomography scans, may be applied to confirm MAT, mesenteric ischemia or mesenteric artery occlusion.
If MAT is diagnosed during early stages of the disease, drug-mediated thrombolysis is indicated. In order to achieve dissolution of the blood clot, heparin, streptokinase, urokinase or alteplase may be directly injected into the affected vessel.
However, moderate to severe cases of MAT, mesenteric ischemia or mesenteric artery occlusion require surgery. The blood clot needs to be removed and if bowel sections have become necrotic, they may need to be resected.