Arterioportal Shunt

Published on 09/08/2015 by admin

Filed under Radiology

Last modified 22/04/2025

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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)

– Wedge-shaped area of increased signal intensity in segment or lobe of shunt
image Venous and delayed phase imaging

– Signal nearly isointense with rest of liver

Ultrasonographic Findings

• Usually US does not detect small, peripheral AP shunts typical of cirrhotic liver
• May detect cause of larger AP shunt

image Mass lesion
image PV thrombosis
image Arterioportal fistula
• Spectral Doppler may reveal “arterialized” waveform in PV for large AP shunt

DIFFERENTIAL DIAGNOSIS

Hypervascular Liver Mass

• Hepatocellular carcinoma, focal nodular hyperplasia, or hypervascular metastases

image Carcinoid, neuroendocrine most common mets
• Usually round or oval, not wedge-shaped
• May show washout on portal venous phase imaging
• May be associated with AP shunting

image Due to hypervascularity (sump effect)
image Or due to compression or occlusion of PV branch
image Or shunting within malignant tumor

Focal Confluent Fibrosis

• Common feature of advanced cirrhosis
• Usually large, wedge-shaped area of decreased density on NECT, increased intensity on T2WI
• Capsular retraction
• Retention of contrast on 10-minute delayed images (CECT or C+ MR)
• Often occurs in segment 4 of liver

Hemangioma

• Usually spherical lesion
• Nodular discontinuous peripheral enhancement
• Capillary or “flash fill” hemangiomas may appear uniformly hyperdense on arterial phase imaging
• Attenuation tracks blood pool on all phases
• May rarely have associated AP shunting

Focal Sparing With Fatty Liver

• Relatively high-attenuation areas of “normal” liver surrounded by low-attenuation fatty liver
• Not really hypervascular foci
• Most often in segments 4A and 4B
• Often around gallbladder fossa

PATHOLOGY

General Features

• Etiology

image Most small arterioportal shunts are incidental findings in cirrhotic liver
image Reflect the altered hemodynamics of cirrhosis

– Hepatic fibrosis → portal hypertension → decreased portal venous flow to liver → increased arterial flow
image Larger AP shunts or transient attenuation differences (THAD [or THID for MR])

– May be classified as neoplastic vs. nonneoplastic according to underlying etiology
– Neoplastic: Hepatocellular carcinoma, cholangiocarcinoma, metastatic, hemangioma
– Nonneoplastic: Lesions with mass effect decreasing PV flow

image Hepatic abscess
image Subcapsular hematoma, biloma, abscess
image Portal or hepatic vein thrombosis
– Trauma

image Shunt or fistula may result from liver biopsy
image Often see premature enhancement of portal vein branch accompanying injured artery
image Usually a transient and insignificant process that resolves spontaneously
image May be classified according to vascular pathways of shunting

– Trans-sinusoidal, via biliary plexus, anomalous venous drainage
image Aberrant venous drainage

– Parabiliary venous plexus

image Includes right gastric vein and veins of pancreaticoduodenal area
image Aberrant blood supply (capsular veins, accessory cystic veins, aberrant right gastric vein) causes systemic venous blood to drain into sinusoids
• Associated abnormalities

image Hepatic tumor
image PV thrombosis
image Hepatic laceration
image Abscess or infection

Gross Pathologic & Surgical Features

• Tumor invading or obstructing veins

image Hepatocellular carcinoma > cholangiocarcinoma or metastases

Microscopic Features

• Small AP shunts are not amenable to biopsy

image Too small
image Cannot be seen on nonenhanced CT or US

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Symptoms are due to underlying cause (cirrhosis, tumor, or infection)
image AP shunt itself is usually asymptomatic
• Other signs/symptoms

image High output congestive failure only with large AP shunts

– May be seen in hereditary hemorrhagic telangiectasia

Demographics

• Age

image Any age
• Epidemiology

image Increased incidence in cirrhotic patients

Natural History & Prognosis

• Poor prognosis if AP shunt is related to PV invasion

image Hepatocellular carcinoma
image Cholangiocarcinoma
image Metastases

Treatment

• Directed at underlying cause

image e.g., infection or tumor
• If hemodynamically significant shunt, embolization may be required

DIAGNOSTIC CHECKLIST

Consider

• For segmental or lobar AP shunt or THAD

image Usually due to portal vein branch occlusion
image Look for bland or tumor thrombus or occlusion

Image Interpretation Pearls

• 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

Reporting Tips

• Do not mistake multiple small AP shunts for multifocal HCC
image
(Left) Arterial phase CECT in a 54-year-old man with chronic hepatitis C, presenting for surveillance of cirrhosis, shows a small, peripheral, hypervascular focus image.

image
(Right) Subsequent portal venous (hepatic parenchymal) phase CECT in the same patient reveals that the small peripheral focus has disappeared. The “lesion” was still gone by a repeat CT 6 months later and is presumably a small arterioportal shunt, which is common in cirrhosis.
image
(Left) Arterial phase CECT in a 46-year-old man with cirrhosis and a history of a prior US-guided liver biopsy shows hyperenhancement of a portion of the lateral segment of the liver image and early enhancement of the portal vein branch that drains this segment image, representing an arterioportal shunt, probably due to the prior liver biopsy at this site.

image
(Right) Portal venous phase CECT in the same patient shows enhancement of the portal vein branch image but otherwise appears normal.
image
(Left) Axial CECT in a 48-year-old woman who presented with progressive liver failure demonstrates an unusually large arterioportal shunt image in the left lobe, most likely the result of a prior liver biopsy at this site.

image
(Right) Axial CECT in the same patient illustrates a small cirrhotic liver with widened fissures and signs of portal hypertension, including splenomegaly and varices image.

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