Portal Vein Thrombosis (PVT)

Definition, Etiology, PathogenesisTop

Thrombosis of the portal vein (PVT) or its intrahepatic branches results in the impairment of blood outflow from the portal venous system and the development of portal hypertension.

Causes: In up to ~50% of cases the cause cannot be determined (idiopathic thrombosis). Possible causes include cirrhosis (the most common known etiology; PVT occurs in <1% of patients with compensated cirrhosis and 8%-25% of those with decompensated cirrhosis), acquired hypercoagulable states (liver or pancreatic cancer, myeloproliferative neoplasms, trauma, inflammatory bowel disease, pancreatitis), inherited prothrombotic states (factor V Leiden; deficiency in protein C, S, or antithrombin protein), and portal vein compression (pancreatic cysts, tumors of the adjacent organs, purulent intra-abdominal lesions).

Clinical FeaturesTop

1. Acute PVT: Clinical presentations range from asymptomatic (presenting later as chronic PVT) to severe abdominal pain, abdominal distention secondary to ileus, and bloody diarrhea if complicated by small bowel infarction. A symptomatic patient with acute PVT often presents within days of the initial thrombotic event. PVT must be differentiated from ischemic colitis and other causes of “acute abdomen.”

2. Chronic PVT develops over several weeks and may be identified by the development of collateral circulation, splenomegaly, and worsening portal hypertension on imaging. Patients often present due to complications of portal hypertension (eg, ascites and variceal bleeding). However, chronic PVT may also be initially clinically silent (no signs or symptoms) and identified incidentally on imaging studies obtained for other indications.

DiagnosisTop

Diagnostic Tests

1. Doppler ultrasonography has sensitivity reported as between 73% and 93%. It visualizes portal vein flow. In patients with acute thrombosis the portal vein may be dilated, but no collateral circulation is seen. In patients with acute or subacute thrombosis, collateral circulation with flow reversal and splenomegaly may be observed.

2. Contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI) can visualize the portal venous system and identify thrombi and collateral circulation, and therefore allow for a more reliable assessment for PVT chronicity (>90% accuracy) and extension to mesenteric veins. These techniques have superseded classical angiography, which is now performed only in exceptional cases.

Differential Diagnosis

Other causes of “acute abdomen” and portal hypertension (see Cirrhosis).

TreatmentTop

1. Management of bleeding esophageal varices: see Gastrointestinal Bleeding.

2. Uncomplicated acute PVT in patients without cirrhosis: Full assessment of hypercoagulable conditions is warranted in collaboration with a hematologist. Antithrombotic treatment is warranted to prevent progression to intestinal ischemia/necrosis (indication for surgical referral and treatment) and the development of chronic PVT and associated noncirrhotic portal hypertension. The length of treatment is in part determined by the precipitating factors (6 months to lifelong if the etiology is irreversible). The choice of therapeutic anticoagulation includes low-molecular-weight heparin (LMWH), a vitamin K antagonist (VKA), and direct oral anticoagulants (DOACs). Data regarding safety and efficacy of DOACs in this patient population are limited.

Indications for local catheter-directed thrombolysis may include thrombus extension with worsening symptoms in patients receiving anticoagulant treatment or threatening bowel infarction related to venous stasis.

3. Acute PVT in patients with cirrhosis: The evidence for treatment of acute PVT in the setting of cirrhosis is predominantly based on observational and case-series studies. The outcomes of these studies suggest that anticoagulation results in higher rates of recanalization (71% vs 42%) with a similar rate of both major and minor bleeding. DOACs are discouraged in patients with decompensated cirrhosis. Traditionally patients with decompensated cirrhosis are treated with LMWH and, less preferably, with a VKA.

In general, PVT is not a contraindication to liver transplant among patients with decompensated cirrhosis. However, complete portal vein occlusion increases surgical complexity by necessitating portal vein reconstruction at the time of transplant and may result in decreased graft survival. Accordingly, initiation of anticoagulation in selected patients with decompensated cirrhosis and PVT can assist in mitigating thrombus propagation to complete occlusion/mesenteric extension and therefore reduce posttransplant complications. The American Association for the Study of Liver Diseases (AASLD) recommends anticoagulation in all eligible patients with a recent partially occlusive (>50% obstructive occlusion of the portal vein) or more extensive disease. In patients with minimally occlusive disease, repeat imaging in 3 months is deemed a reasonable alternative.

4. Chronic PVT (diagnosed on repeated testing or suspected with the presence of collaterals/cavernous malformations): Long-term antithrombotic treatment is very rarely needed and used. Treat complications of portal hypertension. In very selected patients with recurrent bleeding or refractory large-volume ascites despite endoscopic and medical management, portal vein recanalization using catheter directed thrombectomy followed by a transjugular intrahepatic portosystemic shunt (TIPS) may be considered in specialized centers. In patients with thrombosis limited to the splenic vein (SVT), observation alone may be appropriate. However, splenectomy can be considered in the context of bleeding gastric varices secondary to SVT.