Routine blood tests are not helpful in the diagnosis of mesenteric venous thrombosis. The presence of increased serum lactate levels and metabolic acidosis may serve to identify patients with established bowel infarction, but this is a late finding. Abdominal films are abnormal in 50 to 75 percent of patients3 but have findings specific for bowel ischemia in only 5 percent. Blunt, semiopaque indentations of the bowel lumen (thumbprinting) are indicative of mucosal edema, whereas gas in the wall of the bowel (pneumatosis intestinalis) or in the portal vein and free peritoneal air are characteristic of bowel infarction as a result of mesenteric venous thrombosis.10 Barium contrast studies should be avoided in patients suspected of having acute mesenteric venous thrombosis.
Transabdominal color Doppler ultrasonography11 may demonstrate thrombus in the mesenteric veins, but computed tomography (CT) is the test of choice for suspected cases of mesenteric venous thrombosis. Although CT will establish the diagnosis in 90 percent of patients,7,9,12 it is less accurate in those with early thromboses of small mesenteric vessels. An acute thrombus is evident as a central lucency in the mesenteric vein (Figure 2). Other CT findings are enlargement of the superior mesenteric vein and a sharply defined vein wall with a rim of increased density. Persistent enhancement of the bowel wall, pneumatosis intestinalis, and portal-vein gas are late findings.8 The finding of a well-developed collateral circulation in the mesentery and retroperitoneum indicates mesenteric venous thrombosis of more than a few weeks’ duration.
Figure 2. Computed Tomographic Scan of the Abdomen in a Patient with Acute Thrombosis of the Superior Mesenteric Vein Complicating Acute Pancreatitis.
The superior mesenteric vein is enlarged as a result of the thrombosis (curved arrow) and has a sharply defined wall with a rim of increased density. The vein is anterior and to the right of the superior mesenteric artery (arrowhead), which is immediately anterior to the aorta (arrow). Two drains have been placed (open arrows) as a result of pancreatic necrosis from an infection.
Selective mesenteric angiography will demonstrate thrombus in the larger veins, or there may be late visualization of the superior mesenteric vein. Other findings include impaired filling of mesenteric veins, arterial spasm, and prolonged opacification of the arterial arcades.13 Magnetic resonance imaging has excellent sensitivity and specificity for the diagnosis of mesenteric venous thrombosis,14 but its use is cumbersome and the equipment is not universally available. Further advances in the technique may eventually establish a place for magnetic resonance imaging in the diagnosis of mesenteric venous thrombosis.
Abdominal paracentesis is sometimes helpful, because patients with acute mesenteric venous thrombosis may have serosanguineous ascites.3,15 Laparoscopy is best avoided, because the increased abdominal pressure associated with the procedure decreases mesenteric blood flow. Gastroduodenoscopy and colonoscopy are of limited value, given the rarity of colonic and duodenal involvement. Endoscopy with duplex Doppler ultrasonography may detect thrombosis of mesenteric vessels,16 but given the bowel distention associated with this procedure, it is best restricted to patients who do not have acute symptoms.
We recommend abdominal CT in patients who are suspected of having mesenteric venous thrombosis. CT shows the mesenteric vessels and may define the extent of affected bowel, while it rules out other conditions that can cause abdominal pain. Mesenteric angiography should be reserved for patients with a history of thrombophilia in whom small-vessel mesenteric venous thrombosis is suspected.
Once mesenteric venous thrombosis has been confirmed, patients should be screened for hereditary or acquired thrombophilia with tests for protein C and protein S deficiencies, factor V Leiden and other mutations, hyperhomocysteinemia, and paroxysmal nocturnal hemoglobinuria. A bone marrow examination will be useful if a myeloproliferative disorder is suspected. In selected patients, once the acute symptoms have subsided, endoscopy and barium studies may be helpful to rule out the possibility of inflammatory bowel disease.