Arterioportal Shunt

Michael P. Federle, MD, FACR

Brooke R. Jeffrey, MD

Key Facts

Terminology

Communication between branch of hepatic artery and portal venous system

Imaging

Best diagnostic clue
- Wedge-shaped area of hyperattenuation with straight margins seen during arterial phase of CECT or MR
- 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 AP shunts)
- Larger in some cases of post-biopsy AP shunts
- Early enhancement of peripheral portal vein (PV) branches prior to visualization of main PV

Top Differential Diagnoses

Hypervascular liver mass (e.g., HCC)
- Usually round or oval, not wedge-shaped
- Usually shows washout on venous phase
Hemangioma
- Attenuation tracks blood pool on all phases

Pathology

Small AP shunts are not amenable to biopsy
- Too small; invisible on NECT & US

Diagnostic Checklist

Small (< 1.5 cm) AP shunts are common in cirrhosis
- If unassociated with focal lesion on MR, it is probably insignificant
- Follow-up in ˜ 6 months is indicated & adequate

(Left) Seen only on the arterial set of images are multiple peripheral, wedge-shaped, hyperenhancing foci

in this 60-year-old man with cirrhosis due to chronic viral hepatitis. (Right) Axial arterial phase CECT in the same patient shows additional peripheral, wedge-shaped, hypervascular foci

. Also note the large, “corkscrew” hepatic arterial branch

, a typical feature of cirrhosis. The liver has a cirrhotic morphology with wide fissures.

(Left) Axial portal venous phase CECT in the same patient shows none of the peripheral hypervascular lesions, which have become isodense to liver. (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 branch of hepatic artery and portal venous system

IMAGING

General Features

Best diagnostic clue
- Nodular or wedge-shaped area of hyperattenuation with straight margins seen during arterial phase of CECT or gadolinium-enhanced MR
- Becomes isodense to hepatic parenchyma during portal venous phase of CECT or gadolinium-enhanced MR
Location
- Peripherally within hepatic segment or lobe
Size
- Usually ≤ 1.5 cm (e.g., cirrhotic AP shunts)
  - Larger in some cases of post-biopsy AP shunts
  - Transient hepatic attenuation difference (THAD) & transient hepatic intensity difference (THID) can be much larger
    - Can involve entire hepatic segment or lobe
- Morphology
  - Wedge-shaped with straight margins

Imaging Recommendations

Best imaging tool
- Multiphasic CECT or gadolinium-enhanced MR
Protocol advice
- 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
- Early enhancement of peripheral portal vein (PV) branches prior to visualization of main PV
- Peripheral wedge-shaped area of increased attenuation with straight edges within affected segment or lobe
- Aberrant blood supply (capsular veins, accessory cystic veins, aberrant right gastric vein) causes systemic venous blood to drain into sinusoids
  - Hyperdense areas on arterial phase imaging
Portal venous & delayed phase imaging
- Area of previously increased attenuation equilibrates, nearly isodense with rest of liver
- Cause of larger AP shunt (e.g., PV thrombosis, hepatic mass) may be more visible during portal venous phase