What imaging is recommended for a patient with suspected focal portal venous thrombosis, potential underlying liver disease, and a history of malignancy?

Imaging for Suspected Focal Portal Venous Thrombosis with Underlying Liver Disease and Malignancy History

Start with Doppler ultrasound as your first-line imaging modality, followed by multiphase contrast-enhanced CT or MRI with contrast to differentiate benign from malignant thrombus and assess the extent of disease. 1

Initial Imaging Approach

Doppler ultrasound by an experienced operator is the recommended first-line imaging modality for suspected portal vein thrombosis, as it detects portal venous thrombosis in 94% of cases and is superior to CT for demonstrating the extent of thrombosis. 2 In patients with acute or chronic liver disease, Doppler sonography has sufficed to establish or rule out hepatic vascular thrombosis in most patients when the operator is aware of the diagnostic suspicion. 1

Key Ultrasound Findings to Look For:

• Intrahepatic or subcapsular hepatic venous collaterals are found in more than 80% of cases with Budd-Chiari syndrome and are distinctive features that differentiate vascular thrombosis from other liver diseases. 1
• Direct visualization of thrombus within the portal vein and assessment of flow signals. 3

Advanced Cross-Sectional Imaging

When to Proceed Beyond Ultrasound:

If ultrasound findings are indeterminate or you need detailed characterization for multidisciplinary discussion and treatment planning, proceed to either multiphase contrast-enhanced CT or MRI with contrast. 1

Multiphase Contrast-Enhanced CT:

• Order triphasic CT with arterial, portal venous, and delayed phases to differentiate benign from malignant thrombus based on contrast enhancement patterns. 3, 4
• Arterial phase enhancement of the thrombus with delayed washout is highly suggestive of malignant portal vein thrombosis, particularly in patients with hepatocellular carcinoma. 4
• CT detects portal venous thrombosis in 76% of cases but is less accurate than ultrasound for demonstrating the extent of thrombosis. 2
• Critical technical requirement: Use 2.5-5 mm slice thickness for adequate lesion detection. 5

MRI with Gadolinium:

• MRI is more accurate than direct venography for characterizing solid endoluminal material and provides superior soft tissue characterization. 1
• MRI establishes a definitive diagnosis in 95% of liver lesions, significantly higher than CT. 6, 7
• MRI with gadolinium confirmed portal vein thrombus characteristics in documented cases where CT findings needed clarification. 4

Differentiating Benign from Malignant Thrombus

This distinction is critical given your patient's malignancy history:

• Both ultrasound and CT can differentiate venous invasion by tumor from benign thrombosis by detecting solid masses in the liver with contiguous thrombosis of segmental portal veins. 2
• Contrast-enhanced imaging depicts portal vein thrombosis as an endoluminal filling defect best detected in venous phase and can differentiate between non-neoplastic and neoplastic thrombus based on contrast-enhanced uptake. 3
• Arterial enhancement with delayed washout is the key imaging feature that suggests malignant portal vein thrombosis. 4

Role of MRI vs CT in This Clinical Context

Given the combination of suspected liver disease and malignancy history, MRI with contrast is preferred over CT for the following reasons:

• MRI with and without IV contrast receives a rating of 6 out of 9 from the American College of Radiology for chronic liver disease assessment, compared to CT's rating of 5 out of 9. 6
• MRI can simultaneously assess for underlying cirrhosis, characterize liver lesions, and evaluate the portal vein thrombus without radiation exposure. 6, 7
• MRI differentiates between common benign lesions in 70% of cases and establishes definitive diagnosis in 95% of liver lesions. 6, 5

Critical Pitfalls to Avoid

• Do not order CT without contrast alone, as it has minimal diagnostic value with a rating of only 4 out of 9 and provides no specific signs of portal vein thrombosis except under certain specific circumstances. 6, 3
• Avoid CT with and without contrast, as the unenhanced phase adds no diagnostic value and doubles radiation exposure. 6, 7
• Do not rely on single-phase contrast CT; if using CT, always obtain multiphase imaging (arterial and portal venous phases at minimum) as diagnostic accuracy improves from 74-95% to 95.5%. 6, 5
• Be aware that CT has problems with false positive and indeterminate results in approximately 50% of cases when assessing hepatic veins. 1

When Venography May Be Needed

Direct X-ray venography is needed for establishing a diagnosis in difficult cases and for precise delineation of obstructive lesions before planning treatment, particularly when Doppler sonography, MRI, or CT scan does not establish a definitive diagnosis. 1 However, this is typically reserved for cases where noninvasive imaging remains inconclusive and therapeutic intervention is being considered.

Practical Algorithm Summary

1. Start with Doppler ultrasound by an experienced operator 1, 2
2. If ultrasound is diagnostic and shows benign features, proceed with clinical management
3. If ultrasound is indeterminate or suggests malignant features, proceed to:
   • First choice: MRI with and without IV contrast (preferred given liver disease + malignancy history) 1, 6, 7
   • Alternative: Triphasic contrast-enhanced CT (arterial, portal venous, delayed phases) if MRI unavailable 5, 3, 4
4. If cross-sectional imaging remains indeterminate, consider venography for definitive diagnosis and treatment planning 1