Arterioportal Shunt

Published on 09/08/2015 by admin

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Last modified 09/08/2015

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 Wedge-shaped area of hyperattenuation with straight margins seen during arterial phase of CECT or MR

image Becomes isodense to hepatic parenchyma during portal venous phase of CECT or gadolinium-enhanced MR
• Peripherally within hepatic segment or lobe
• Usually ≤ 1.5 cm (e.g., cirrhotic arterioportal [AP] shunts)

image Larger in some cases of post-biopsy AP shunts
image Early enhancement of peripheral portal vein (PV) branches prior to visualization of main PV

TOP DIFFERENTIAL DIAGNOSES

• Hypervascular liver mass (e.g., hepatocellular carcinoma [HCC])

image Usually round or oval, not wedge-shaped
image Usually shows washout on venous phase
• Hemangioma

image Attenuation tracks blood pool on all phases
• Focal sparing with fatty liver

image Not really hypervascular foci
image Relatively high-attenuation areas of “normal” liver surrounded by low-attenuation fatty liver

PATHOLOGY

• Small AP shunts are not amenable to biopsy

image Too small; invisible on NECT and US

DIAGNOSTIC CHECKLIST

• Small (< 1.5 cm) AP shunts are common in cirrhosis

image If unassociated with focal lesion on MR, it is probably insignificant
image Follow-up in ∼ 6 months is indicated and adequate
• Do not mistake multiple small AP shunts for multifocal HCC
image
(Left) Seen only on the arterial set of images are multiple peripheral, wedge-shaped, hyperenhancing foci image in this 60-year-old man with cirrhosis due to chronic viral hepatitis.

image
(Right) Axial arterial phase CECT in the same patient shows additional peripheral, wedge-shaped, hypervascular foci image. Also note the large, “corkscrew” hepatic arterial branch image, a typical feature of cirrhosis. The liver has a cirrhotic morphology with wide fissures.
image
(Left) Axial portal venous phase CECT in the same patient shows none of the peripheral hypervascular lesions, which have become isodense to liver.

image
(Right) Axial delayed phase CECT shows no washout or other evidence of the focal peripheral lesions seen on arterial phase. AP shunts are common within the cirrhotic liver. Imaging features that favor AP shunt over HCC include peripheral, subcapsular location, small size, wedge shape, and no corresponding lesion on venous or delayed phase imaging.

TERMINOLOGY

Abbreviations

• Arterioportal (AP) shunt

Definitions

• Communication between a branch of hepatic artery and portal venous system

IMAGING

General Features

• Best diagnostic clue

image Nodular or wedge-shaped area of hyperattenuation with straight margins seen during arterial phase of CECT or gadolinium-enhanced MR
image Becomes isodense to hepatic parenchyma during portal venous phase of CECT or gadolinium-enhanced MR
• Location

image Peripherally within hepatic segment or lobe
• Size

image Usually ≤ 1.5 cm (e.g., cirrhotic AP shunts)

– Larger in some cases of post-biopsy AP shunts
– Transient hepatic attenuation difference (THAD) and transient hepatic intensity difference (THID) can be much larger

image Can involve entire hepatic segment or lobe
• Morphology

image Wedge-shaped with straight margins

Imaging Recommendations

• Best imaging tool

image Multiphasic CECT or gadolinium-enhanced MR
• Protocol advice

image Arterial phase acquisition of CECT or MR at 25-35 seconds after injection

– Followed by venous phase (60-70 seconds) and delayed phase (∼ 120 seconds)

CT Findings

• Arterial phase imaging

image Early enhancement of peripheral portal vein (PV) branches prior to visualization of main PV
image Peripheral wedge-shaped area of increased attenuation with straight edges within affected segment or lobe

– Hyperdense areas on arterial phase imaging
• Portal venous and delayed phase imaging

image Area of previously increased attenuation equilibrates, becomes nearly isodense with rest of liver
image Cause of larger AP shunt (e.g., PV thrombosis, hepatic mass) may be more visible during portal venous phase

MR Findings

• T1WI

image T1WI and T2WI usually normal for nontumoral causes of AP shunts
• T2WI

image Rarely slight increase in T2 signal in affected lobe or segment of nontumoral shunts
image Underlying mass may cause abnormal T2 signal with AP shunts related to hepatic masses or tumors
• Dynamic gadolinium-enhanced MR

image Arterial phase imaging (25-35 seconds after injection)

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