Arterioportal shunt (AP shunt) is an abnormal communication between the hepatic artery and portal vein branches. It shows transient arterial-phase subcapsular wedge or triangular enhancement (THAD — transient hepatic attenuation difference) that completely disappears on portal venous/delayed phases. Common in cirrhotic liver and represents the most critical differential diagnosis from HCC. Arterioportal shunt is a vascular phenomenon, not a lesion — no treatment is required.
Age Range
30-80
Peak Age
55
Gender
Equal
Prevalence
Common
Arterioportal shunt occurs through a small abnormal communication (micro-fistula) between the hepatic artery and portal vein branches. Through this fistula, arterial blood enters portal vein branches early, creating transient arterial hyperperfusion in local hepatic parenchyma. In cirrhotic liver, portal venous flow is already reduced — the arterial compensation mechanism is active and micro-fistulas are facilitated. In arterial phase, contrast reaches the parenchyma in the fistula region early (hyperintensity), but in portal venous phase, portal perfusion equilibrates in surrounding parenchyma and enhancement disappears. The wedge shape reflects the drainage territory of the affected portal vein branch — segmental perfusion anomaly.
Subcapsular wedge/triangular enhancement area in arterial phase — completely disappearing on portal venous/delayed phases. Its non-nodular shape conforming to anatomic vascular distribution and transient character are pathognomonic findings of AP shunt. This finding reflects only vascular perfusion anomaly — there is no underlying true lesion.
Subcapsular wedge or triangular-shaped enhancement area in arterial phase. Sectoral, not nodular — conforms to vascular distribution. Classic CT finding of THAD.
Report Sentence
A subcapsular wedge-shaped transient enhancement area is seen in arterial phase, consistent with arterioportal shunt (THAD).
Arterial enhancement completely disappears on portal venous phase — the area becomes isointense/isoattenuating with surrounding parenchyma. This 'transience' is the diagnostic key of AP shunt.
Report Sentence
The arterial enhancement area has completely disappeared on portal venous phase, appearing isoattenuating with surrounding parenchyma.
Wedge-shaped hyperintense area on MRI arterial phase. Visualized with better soft tissue contrast compared to CT.
Report Sentence
A subcapsular wedge-shaped hyperintense area is seen on MRI arterial phase.
Normal signal on hepatobiliary phase (gadoxetic acid) — isointense with surrounding parenchyma. Hepatocytes in the THAD region are healthy, so OATP function is preserved.
Report Sentence
Normal signal is seen in the same region on hepatobiliary phase, indicating preserved hepatocyte function and consistency with arterioportal shunt.
No diffusion restriction on DWI. AP shunt is not a cellular lesion, so increased cellularity or cytotoxicity is not expected.
Report Sentence
No diffusion restriction is observed in the corresponding region on DWI, with no findings favoring a cellular lesion.
Focal flow increase or pulsatile portal vein flow may be detected on Doppler US in larger forms of arterioportal shunt. Small shunts are not visible on US.
Report Sentence
Arterial waveform is observed in portal vein branches on Doppler US, which may be consistent with arterioportal shunt.
Criteria
Small subcapsular wedge-shaped THAD. Most common type. Common in cirrhotic liver, benign and clinically insignificant.
Distinct Features
Usually <2 cm, may be single or multiple. Not detectable on Doppler. No follow-up needed.
Criteria
AP shunt around HCC or other hypervascular tumor. When tumor invades portal vein branches, compensatory arterial perfusion increases.
Distinct Features
Nodular lesion (HCC) present within or adjacent to shunt area. Portal vein thrombosis may accompany. Elevates to LI-RADS 5.
Criteria
AP shunt developing after biopsy, ablation, or TACE. Occurs due to iatrogenic vascular damage.
Distinct Features
Localized to procedure site. Recognized by correlation with procedure history. Usually closes spontaneously over time.
Distinguishing Feature
HCC is nodular in shape (not wedge-shaped), shows washout on portal/delayed phase (in AP shunt it becomes isointense, NOT hypodense), is hypointense on hepatobiliary phase (isointense in AP shunt), shows diffusion restriction on DWI. T2 hyperintensity and capsule are specific to HCC.
Distinguishing Feature
FNH is nodular, shows central scar, is hyperintense on hepatobiliary phase (retention with gadoxetic acid). AP shunt is wedge-shaped, not nodular, and has no central scar. FNH typically occurs in non-cirrhotic liver.
Distinguishing Feature
HGDN is nodular, hypointense on hepatobiliary phase (OATP loss), T1 hyperintense, and may show mild T2 hyperintensity. AP shunt is wedge-shaped, isointense on hepatobiliary phase, and shows no significant T1/T2 signal anomaly.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upArterioportal shunt is a vascular phenomenon, not a lesion — no treatment or follow-up is required. Its main clinical importance is correct differentiation from HCC. In cirrhotic liver, it should be remembered that suspicious areas detected on US screening may be THAD. Tumoral AP shunt (HCC-associated) is different — treatment of the underlying tumor is required. In reports, the phrase 'THAD consistent with arterioportal shunt — not a lesion' clarifies clinical management.
No clinical significance; not a true lesion. Requires no treatment or follow-up. However, differentiation from HCC in cirrhotic liver is critical. Classified as LR-1 (definitely benign) in LI-RADS v2018. Disappearance on portal/delayed phase is diagnostic.