Diagnostic Ultrasound - Abdomen and Pelvis

Portal Vein Occlusion
TERMINOLOGY
Abbreviations
• Portal vein (PV)
Definitions
• Obstruction of portal vein, most commonly due to
thrombosis
• Cavernous transformation of PV: Portal venous
collateralization
IMAGING
General Features
• Best diagnostic clue
○ Absent blood flow within PV on color or spectral Doppler
US
○ Cavernous transformation of PV
• Location
○ Main portal vein &/or right and left branches
• Size
○ Acute thrombosis; PV diameter may be enlarged
○ Chronic occlusion; PV diameter small, echogenic, or not
visible
Ultrasonographic Findings
• Grayscale ultrasound
○ Normal PV readily seen; nonvisualization suggests
occlusion
○ Faintly echogenic material within PV lumen
○ Cavernous transformation of PV
– Multiple tubular channels along usual course of
thrombosed PV
– Seen with subacute and especially chronic occlusion
○ Possible findings of pancreatitis if PV thrombosis due to
this condition
○ If associated with tumor invasion of PV (tumor
thrombus), may see heterogeneous, often expansile
intraluminal soft tissue mass
• Pulsed Doppler
○ Absent Doppler signals in PV
○ Continuous flow in collaterals (no respiratory variation)
• Color Doppler
○ No color flow in PV
○ If associated with tumor invasion of PV (tumor
thrombus)
– May see tiny feeding vessels producing dot-dash
pattern
– Low-resistance arterial flow in feeding tumor vessels
– Not consistently seen
○ Reversed flow in splenic vein; possibly superior
mesenteric vein
○ Hepatopetal flow in cavernous transformation
○ Hepatofugal flow in portosystemic collaterals (due to
portal hypertension)
○ Absent flow in hepatic vein or inferior vena cava (IVC) if
PV occlusion secondary to these conditions
Imaging Recommendations
• Best imaging tool
○ Color/spectral Doppler sonography for surveillance and
initial diagnosis
○ CECT/MR
– Comprehensive evaluation: Extent of occlusion and
collateralization
– Evaluation of cause and underlying condition
• Protocol advice
○ Technical errors are major diagnostic impediment
– Check to see if flow can be detected in other vessels
at equivalent depth
DIFFERENTIAL DIAGNOSIS
Hepatic Vein/IVC Occlusion
• Causes slow flow in PV
• Possible secondary PV occlusion
Splenic Vein Occlusion
• No flow/nonvisualization of splenic vein
• Extensive left-sided collaterals
• Confirm that portal vein is patent
False-Positive PV Occlusion
• Poor ultrasound technique
○ Inadequate Doppler angle
○ Wrong velocity scale
○ Insufficient color/spectral Doppler gain
○ Wall filter too high
• Slow flow state
○ Very slow, or to-and-fro PV flow
○ No flow detected with color Doppler, sometimes
spectral Doppler also
○ Usually due to cirrhosis/portal hypertension
False-Negative PV Occlusion
• Poor ultrasound technique
○ Nonocclusive thrombus
○ Too much color gain: "Blooming" of color beyond flow
stream
– Blooming overwrites grayscale image, obscuring
thrombus
○ Less likely with tumor invasion, which typically is
occlusive
Nonocclusive Thrombosis
• Variable degree of obstruction
• May be inapparent clinically
Dilated Bile Duct
• Patent adjacent PV seen with color Doppler
PATHOLOGY
General Features
• Etiology
○ Thrombosis
– Combination of etiologic factors is common
– Stasis: Sinusoidal obstruction as in cirrhosis; hepatic
vein or IVC obstruction
– Severe dehydration (especially in children)
– Hypercoagulable states (genetic/neoplasm-related)
– Pancreatitis: Portal/splenic vein inflammation
(phlebitis) → thrombosis
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