What is the best initial test to evaluate a portal venous thrombus?

Evaluation of Portal Venous Thrombosis

Doppler ultrasound should be used as the first-line diagnostic test for evaluating portal venous thrombosis, followed by contrast-enhanced CT for confirmation and assessment of extension. 1

Initial Diagnostic Approach

Primary Diagnostic Test

• Doppler ultrasound is the recommended first-line investigation for suspected portal vein thrombosis 1
  • Advantages: Non-invasive, widely available, no radiation exposure
  • Can detect absence of flow within the portal vein
  • May show hyperechoic thrombus in the portal lumen (though this finding may be lacking)
  • Allows assessment of portal vein patency with high negative predictive value (98%) 2

Confirmatory Testing

• Contrast-enhanced CT scan should be performed to:
  • Confirm diagnosis when ultrasound is positive or equivocal 1
  • Assess the extent of thrombosis (particularly extension to mesenteric veins)
  • Evaluate for underlying causes (local factors, malignancy)
  • Identify complications (bowel ischemia, congestion)
  • Portal phase imaging is crucial for accurate diagnosis 1

Diagnostic Pitfalls to Avoid

1. Timing of CT acquisition: Images must be acquired during the portal phase, not arterial phase 1

   • Late arterial phase imaging can lead to false positive diagnosis of thrombosis
   • Low portal flow can create filling defects mimicking thrombosis

2. Relying solely on ultrasound: While ultrasound has high sensitivity (89%), it has limitations 2:

   • Operator-dependent
   • May miss partial thrombosis
   • False negatives with sluggish flow
   • Limited visualization in obese patients or excessive bowel gas

3. Missing thrombus extension: Failure to assess extension to mesenteric veins can lead to missed diagnosis of intestinal ischemia 1

   • Distal thrombosis (occlusion of second-order radicals of superior mesenteric vein) is associated with intestinal resection 1

Additional Diagnostic Considerations

MR Imaging

• MR venography may be used as an alternative when:
  • CT is contraindicated (contrast allergy, pregnancy, renal insufficiency)
  • Further characterization of thrombus age is needed
  • Biliary complications are suspected (MR cholangiography) 1

Contrast-Enhanced Ultrasound

• Can help differentiate between benign and malignant portal vein thrombosis 3
• Particularly useful in cirrhotic patients with suspected hepatocellular carcinoma invasion
• Shows 100% sensitivity and specificity for malignant thrombus when positive enhancement is observed 3

Invasive Testing

• Angiography may be indicated when:
  • Noninvasive tests are inconclusive or contradictory 4
  • Noninvasive tests indicate occlusion but confirmation is clinically crucial 4
  • Therapeutic intervention is planned (e.g., thrombolysis)

Follow-up Imaging

• Perform CT scan to assess recanalisation of the portal venous system at 6-12 months 1
• For pediatric patients, start screening at 6 months after the event, then annually for 5 years 1
• Screen for gastroesophageal varices in unrecanalised patients 1

Summary of Diagnostic Algorithm

1. Initial test: Doppler ultrasound of portal venous system
2. If positive or equivocal: Proceed to contrast-enhanced CT (portal phase)
3. If CT confirms thrombosis: Assess extension and complications
4. If diagnostic uncertainty persists: Consider MR venography or invasive angiography
5. Follow-up imaging: CT at 6-12 months to assess recanalisation

This approach provides the most comprehensive evaluation while minimizing unnecessary radiation exposure and invasive procedures, directly addressing the mortality and morbidity risks associated with portal venous thrombosis.