Risk Factors

The most prevalent hematologic inherited or acquired thrombotic disorders include protein C and S deficiency, factor V Leiden, antiphospholipid antibody, and antithrombin III deficiency. Other hematologic disorders such as myeloproliferative disorders, polycythemia vera, essential thrombocythemia, and paradoxical nocturnal hemoglobinuria are also associated with the diagnosis. The use of oral contraceptives is a well-recognized risk factor and accounts for up to 10% of cases in some series.

Nonhematologic etiologies include conditions such as pancreatitis, pancreatic cancer and other malignancies, peritonitis, diverticulitis, inflammatory bowel disease, splenectomy, cirrhosis, and blunt abdominal trauma. Low-flow states from heart failure and even severe dehydration in healthy people have been associated with mesenteric vein thrombosis.

Clinical Presentation

The clinical presentation of mesenteric vein thrombosis depends on the initiating thrombotic site and the rapidity with which it propagates. Patients present, in decreasing prevalence, with subacute, acute, or chronic symptoms. Mesenteric vein thrombosis that begins in the most peripheral veins and then progresses centrally often appears as a subacute disorder characterized by slowly worsening abdominal pain, distention, and progressive fluid sequestration within the wall of affected segments. The pain is often diffuse and colicky. Most patients with mesenteric vein thrombosis experience slowly worsening symptoms and generally present at least 48 hours after initial symptoms. Clinically important lower or upper gastrointestinal bleeding is rare, but occult blood in the stool is detectable in up to 50% of cases.

When larger segments of bowel are affected and collateral venous channels are compromised, a more acute syndrome is encountered, with severe and sudden symptoms more consistent with arterial ischemia. Patients present with severe abdominal pain that is classically described as out of proportion to the abdominal examination. The risk of hemorrhagic infarction is much higher in such patients and increases still more when arterial compromise follows owing to venous outflow obstruction.

Chronic thrombotic occlusions of the portal or superior mesenteric veins are most often asymptomatic and are only discovered serendipitously through imaging studies targeting inflammatory bowel disease, pancreatitis, or other abdominal pathology. These patients generally do not have abdominal pain but can experience complications of extrahepatic portal hypertension. Although hypercoagulable states are less common in this group, it is prudent to evaluate such predispositions.

Diagnosis

Early recognition of mesenteric vein thrombosis is confounded by the nonspecificity of symptoms and the overlying complaints referable to other intraabdominal conditions. Perhaps the best diagnostic clue is a history of a coagulation disorder or previous thrombotic episodes. As in all types of mesenteric vascular disorders, laboratory studies are not particularly helpful early in the disease process. Leukocytosis is generally not prominent until bowel infarction has occurred. Hyperamylasemia is very nonspecific. Hemoconcentration is often seen as a result of fluid sequestration within the bowel wall and lumen but may be dismissed owing to a lack of awareness of the premorbid hematocrit.

Plain radiographs are rarely diagnostic, but they are required to exclude other pathology such as a ruptured viscus or renal calculi. The most common if subtle sign of mesenteric vein thrombosis is thickening of the bowel wall and mucosal edema. Pneumatosis intestinalis and portal vein gas only occur late in the disease and are grave prognostic signs.

Computed tomography (CT) scans with venous delay is the most commonly used diagnostic modality for mesenteric vein thrombosis and compares favorably in sensitivity and specificity to selective mesenteric arteriogram with venous runoff (Figure 1). In most series, the sensitivity of CT in detecting acute thrombus of medium-sized or large vessels is 90% or greater. The diagnosis is made by noting central lucencies in the major veins (evident in up to 75% of cases) and correlating such findings with evidence of ascites, bowel or mesenteric edema (stranding), and inflammation. Water can be given orally to enhance the evaluation of the mucosa. Transmural infarction is suspected when a lack of bowel wall enhancement is seen. Other imaging modalities such magnetic resonance imaging (MRI) and ultrasonography are occasionally helpful in selected cases but do not supplant the utility of CT.

Diagnostic endoscopy and laparoscopy should be avoided in acute settings because they can increase bowel distention and decrease venous return, respectively. In cryptic presentations, abdominal paracentesis can help confirm the diagnosis by demonstrating serosanguineous ascites.

Medical Management

The majority of patients with acute and subacute mesenteric vein thrombosis unassociated with bowel infarction or perforation can be initially managed medically. The single most important therapy is immediate anticoagulation with heparin to minimize progression of thrombosis. In fact, full anticoagulation should be administered even if surgery is contemplated; this usually entails a bolus appropriate for body mass and subsequent infusion, sustaining a partial thromboplastin time at least twice the normal level. Important supportive therapies include vigorous fluid resuscitation, nasogastric tube placement, and complete bowel rest.

If medical management is successful, distention and abdominal pain should slowly resolve over 5 to 10 days, and small feedings can begin. Patients should be transitioned to an oral anticoagulant such as warfarin, which is continued for 1 year and potentially permanently, depending on the detection of a hypercoagulable state. Importantly, family members should undergo comprehensive laboratory testing for coagulation disorders.