Mesenteric vein thrombosis is an acute, subacute or chronic thrombosis of the superior mesenteric vein or inferior mesenteric vein or its branches. Mesenteric vein thrombosis may present as acute abdominal pain or may be asymptomatic and discovered unexpectedly on abdominal imaging. The incidence of mesenteric vein thrombosis is 1 per 5000-15000 in hospitalized patients; 1 per 1000 in patients undergoing emergency open abdominal surgery for acute abdominal conditions. The incidence of mesenteric vein thrombosis has been increasing in the last 40 years, possibly also due to the increasing use of abdominal CT.
The age of onset varies, depending on the different mechanisms of mesenteric vein thrombosis pathogenesis, with the most common cases occurring between 40 and 60 years of age. It is slightly more frequent in men. Chronic mesenteric vein thrombosis is often asymptomatic, so its incidence may be underestimated.
Why does mesenteric thrombosis occur?
Mesenteric vein thrombosis is often the result of a combination of hypercoagulation, endothelial injury, and stagnant blood flow, all of which can be local problems or systemic problems. In patients with an inherited hypercoagulable state, mesenteric vein thrombosis can occur in response to transient or mild factors. Other patients can result from inflammatory bowel disease, intra-abdominal infection or abdominal trauma. Abdominal surgery can lead to both endothelial injury and inflammation, which can also lead to mesenteric vein thrombosis. Between 4% and 16% of cases of acute mesenteric vein thrombosis are malignant. Up to 37% of cases of mesenteric vein thrombosis are idiopathic.
Inflammation and other local factors often lead to thrombosis of large mesenteric veins, whereas systemic hypercoagulability is more commonly seen to lead to thrombosis of smaller vessels. Normal mesenteric venous drainage is accompanied by mesenteric arterial circulation. In the resting state, the intestine can tolerate a severe reduction in blood flow, requiring only 20% of the capillaries to provide the oxygen supply needed by the tissues. Even under stress, the intestinal mucosa can enhance oxygen extraction. However, the ability of intestinal capillaries to provide oxygen is depleted under sustained ischemia due to thrombotic obstruction. The inflammatory response can lead to intestinal mucosal necrosis and eventual destruction of the mucosal barrier. The intestinal bacteria migrate and enter the bloodstream and abdominal cavity, leading to systemic infection, hemodynamic disturbances, and multi-organ system failure.
The superior mesenteric vein is involved in 95% of cases of mesenteric vein thrombosis, and only 4% to 6% of cases involve the inferior mesenteric vein (the distal colon that supplies abundant collateral circulation). Acute mesenteric vein thrombosis is typically due to new thrombosis of the superior mesenteric vein or its branches in the absence of collateral circulation. It can involve the ileum (64% to 83%), jejunum (50% to 81%) and duodenum (4% to 8%). In subacute mesenteric vein thrombosis, venous obstruction leads to ischemia, but sufficient venous collateral circulation allows blood flow to be restored. With chronic mesenteric vein thrombosis, collateral vessels open after a certain time and become an alternative route for venous drainage. Good collateral circulation delays the onset of ischemia.
What are the manifestations of mesenteric thrombosis?
The symptoms of mesenteric vein thrombosis often lack specificity. The severity depends on the speed of thrombosis and the extent and location of vascular involvement. Acute mesenteric vein thrombosis often presents with abdominal pain, similar to mesenteric artery ischemia, which begins with a sudden spasmodic abdominal pain during the ischemic phase. Acute obstruction of the portal vein leads to abdominal distention and ascites. If not treated promptly, ischemia induces mucosal barrier disruption, leading to peritonitis or systemic infection, and ultimately to hemodynamic instability and multi-organ system failure. Acute mesenteric vein thrombosis is hemodynamically unstable in 6 to 29% of cases at the onset.
In subacute and chronic mesenteric vein thrombosis, patients may be asymptomatic or present with vague intermittent abdominal pain due to the presence of collateral circulation.1 In one study, more than 50% of patients with subacute mesenteric vein thrombosis had a history of intermittent abdominal pain in the month prior to presentation. Patients with chronic mesenteric vein thrombosis may also present with bleeding due to portal hypertension.
How is mesenteric thrombosis diagnosed?
The diagnosis of mesenteric vein thrombosis is often delayed because the symptoms are not specific. For example, abdominal pain resulting from mesenteric vein thrombosis after abdominal surgery is often incorrectly attributed to postoperative discomfort. Abdominal pain in inflammatory bowel disease is often attributed to exacerbation of the disease. In contrast, early diagnosis is essential to prevent delayed treatment and worsening prognosis.
The clinical examination of the abdomen presents in a variety of ways and on palpation can be nonspecific discomfort or abdominal pain that does not match the examination. In the initial phase of ischemia, the pain can be intense and constant to palpation, without signs of peritoneal involvement. There is often no fever or hypothermia, unless peritonitis or systemic infection occurs. Ischemia progresses to necrosis and peritoneal signs appear, including muscle guards, rebound pain, and muscle tension.
Laboratory tests have no sensitive or specific laboratory indicators for the diagnosis of mesenteric vein thrombosis. Although elevated serum lactate levels and metabolic acidosis are associated with increased mortality, normal serum lactate levels and pH do not exclude mesenteric vein thrombosis. Severe leukocyte elevation, often exceeding 20,000/uL, may be the only laboratory test abnormality in the early stages of the disease. Three studies have shown blood in the feces in 80% to 100% of patients with mesenteric vein thrombosis. d-dimer tests are nonspecific and can be elevated in other abdominal conditions such as infection or inflammation.
Imaging CT: Contrast-enhanced CT should be performed for mesenteric vein thrombosis. the characteristic presentation is a filling defect of the mesenteric veins. Other nonspecific manifestations are thickening of the intestinal wall, indistinct intestinal margins, ascites, and thickening of the mesentery. CT angiography has a sensitivity and specificity of 93% and 100%, respectively, with positive and negative predictive values ranging from 94% to 100%.
Magnetic resonance venography: The advantages of magnetic resonance venography are the reduction of radiation and the possibility of using it in patients with iodine contrast allergy. However, patients with acute mesenteric vein thrombosis with severe abdominal pain may have difficulty tolerating prolonged MRV examinations. For patients with chronic mesenteric vein thrombosis with milder symptoms, MRV is an excellent examination.
Other imaging techniques: isotope examination is rarely used for the diagnosis of mesenteric vein thrombosis because of its poor sensitivity and high equipment requirements. In patients with acute abdominal pain who are first examined by means of Doppler ultrasound, large emboli may be detected, but emboli in small vessels cannot be examined. With the widespread use of CT, mesenteric angiography is now rarely used to diagnose mesenteric vein thrombosis.
How is mesenteric thrombosis treated?
The primary treatment goal for acute mesenteric vein thrombosis is reperfusion of the involved bowel segment to prevent intestinal infarction. Initial treatment for all patients should include fasting, gastrointestinal decompression, intravenous rehydration, prophylactic antibiotic application, and injectable anticoagulation (e.g., intravenous plain heparin or injectable low molecular weight heparin). Further treatment, including thrombolysis, embolization, and bowel resection, should be used in patients who are hemodynamically unstable or whose symptoms are difficult to control.
Anticoagulation
Systemic anticoagulation is the key to the treatment of mesenteric vein thrombosis. Anticoagulation prevents embolus extension, promotes intestinal reperfusion, and reduces complications and mortality. Anticoagulation allows for venous recanalization. For patients who may require surgical treatment or application of thrombolytic therapy, intravenous normal heparin due to low molecular weight heparin.
Acute, subacute and chronic mesenteric vein thrombosis all require anticoagulation. Several small retrospective studies illustrate the benefit of anticoagulation in acute mesenteric vein thrombosis. However, these patients may require further intervention (e.g., thrombolysis or surgery) to prevent death. In chronic mesenteric vein thrombosis, anticoagulation may promote revascularization and prevent new thrombosis. A study of chronic mesenteric vein thrombosis showed partial or complete recanalization of obstructed vessels in 93% of patients. Studies are lacking in patients with chronic mesenteric vein thrombosis leading to portal hypertension, although the increased risk of bleeding from esophageal varices should be considered.
For long-term treatment, warfarin anticoagulation with a target INR of 2.0 to 3.0 is the standard of care. For mesenteric vein thrombosis, new oral anticoagulants have not been studied. The recommended anticoagulation course is 6 months for those with a reversible etiology. Prolonged anticoagulation is often required in those with a thrombophilic base or idiopathic mesenteric vein thrombosis.
Thrombolysis
Catheter-based thrombolysis is indicated for severe acute mesenteric vein thrombosis where anticoagulation has failed. Even if thrombus lysis is not visible on imaging, subcatheter thrombolysis may result in improved symptoms, decreased chance of bowel resection, and fewer complications. Despite the overall improvement in patient status, the chance of complications (mainly bleeding) with subcatheter thrombolysis is estimated to be as high as 60%. Therefore, subcatheter thrombolysis is usually recommended only for patients whose symptoms do not resolve with anticoagulation, but who do not require surgical intervention. Contraindications to subcatheter thrombolysis include a history of stroke or intracranial hemorrhage, primary or metastatic malignancy of the central nervous system, active or recent bleeding, recent surgery, recent trauma, and mesenteric infarction.
Embolization
Subcatheter embolization can be used as an adjunct to thrombolytic therapy and anticoagulation, especially for large vessel thrombosis, and this method can rapidly improve venous patency. Methods include percutaneous mechanical embolization, angioplasty and stenting, and aspiration. Embolization is most effective for acute emboli.
Surgery
Recent studies suggest that nonsurgical treatment improves survival and reduces complications more than surgical treatment. However, surgical treatment is still required for cases of mesenteric vein thrombosis with hemodynamic instability, peritonitis, and intestinal necrosis. Surgical approaches include dissection or laparoscopy. The necrotic bowel segment is excised, but the questionable bowel segment is usually preserved. This more conservative strategy is preferred over extensive bowel segment resection, primarily because of the long-term risk of short bowel syndrome. Because of the potential for reinfarction of the surviving bowel segment, many surgeons perform a second-stage exploration 12 to 48 hours later to reevaluate the area of the previously suspected segment. Up to 50% of patients require further resection of the segment at the second stage of exploration.
Is mesenteric thrombosis dangerous if it occurs?
Despite significant advances in the treatment of thromboembolic disease over the past 40 years, the average 30-day mortality rate in severe cases of acute mesenteric vein thrombosis is as high as 32.1%. Prognostic factors include patient age, comorbidities, time to diagnosis, and time to hemodialysis. Mortality is <10% in those who receive rapid diagnosis and treatment. If treatment was delayed by 6 to 12 hours, the mortality rate rose to 50-60%. If treatment was delayed >24 hours, the mortality rate was 80 to 100 percent. Surprisingly, non-obstructive mesenteric vein thrombosis has a higher mortality rate compared to the obstructive subtype, which may be due to the delay in treatment due to its atypical symptoms. For chronic mesenteric vein thrombosis, the 5-year survival rate is 78% to 82%. The prognosis of chronic mesenteric vein thrombosis depends on the nature and severity of the underlying disease.
The recurrence rate of mesenteric vein thrombosis after bowel resection is as high as 60%, with the majority of cases recurring in the anastomosed bowel segment. Some recent studies suggest a lower recurrence rate with thrombolytic therapy with or without embolization.