Hepatic arterioportal shunts: dynamic CT and MR features

Abstract

With the increased temporal resolution available in dynamic computed tomography (CT) and magnetic resonance imaging (MRI), hepatic arterioportal shunts are now more frequently encountered than in the past. The condition occurs in various hepatic diseases in which portal or hepatic venous flow is compromised. The underlying mechanism and the degree of shunt affect its appearance at dynamic imaging. The dynamic CT and MRI findings have been summarized as early enhancement of peripheral portal veins, and wedge-shaped transient parenchymal enhancement during the hepatic arterial phase. Recognition of arterioportal shunt can suggest the presence of a previously unsuspected disorder and avoids false-positive diagnosis or overestimation of a hepatic disease. Familiarity with the pathophysiology of arterioportal shunt also allows investigation of the hepatic hemodynamic changes occurring in various hepatic diseases.

Fig. 1

Portal vein thrombosis occurring in pylephlebitis. A. CT scan obtained during hepatic arterial phase shows transient high attenuation of the right anterior segments of the right lobe and segments III and IV (arrows). B. Portal venous phase image shows bland thrombi, producing inflow obstruction, within the portal veins (arrows). The portal vein supplying segment II is patent (arrowheads). Note that the straight border of transient hepatic attenuation difference on the hepatic arterial phase image (arrows in (A)) intersects the hepatic vein (small arrow in (B)).

Fig. 2

Attenuation differences secondary to hepatic vein obstruction in a transplanted liver. A. CT scan obtained during portal venous phase shows hypoattenuation of the anterior segment of the transplanted right lobe despite normal enhancement of the portal veins (arrowheads) inside the corresponding area. B. CT scan obtained during the equilibrium phase reveals thrombosed hepatic vein (arrow) which was ligated during surgery. The anterior segment of the transplanted right lobe appears hyperattenuated, producing a negative image of (A). Note that the straight border (small arrows in (A) and (B)) of transient hepatic attenuation difference intersects the portal veins (open arrows in (A) and (B)).

Fig. 3

Arterioportal fistula in a 42-year-old man with symptoms of portal hypertension such as recurrent gastrointestinal bleeding and ascites. He had undergone percutaneous liver biopsy seven years earlier. A. A maximum-intensity projection image of CT scans obtained during hepatic arterial phase shows hyperattenuation of the right lobe of the liver, with an enlarged hepatic artery (arrowheads). B. Celiac angiogram demonstrates that shunted arterial flow from the fistulous point (arrow) is instantaneously drained into portal branches in the entire right lobe of the liver. Subsequent embolization of the fistula relieved this patient's symptoms.

Fig. 4

Arterioportal shunt secondary to hemangioma in a patient with pancreatic carcinoma. A. CT scan obtained during hepatic arterial phase shows a hemangioma (arrow) at the right lobe of the liver. B. Follow-up CT scan obtained six months later shows wedge-shaped transient hyperattenuation of the adjacent parenchyma (arrows), with early opacification of the peripheral portal veins (arrowheads). Another area of transient parenchymal enhancement is apparent (open arrow), and was secondary to another small hemangioma in contiguous section (not shown). The change observed in the degree of Arterioportal shunt between figures (A) and (B) might be due to diminished portal blood flow caused by severe stenosis of the main portal vein (not shown).

Fig. 5

Arterioportal shunt secondary to percutaneous ethanol injection therapy in a patient with HCC. A. CT scan obtained during portal venous phase shows a perfusion defect at the site of previous percutaneous ethanol injection therapy (arrows), as well as multiple nodular tumors with iodized-oil uptake (arrowheads). An extrahepatic metastatic nodule, probably located at the previous needle tract for another percutaneous ethanol injection therapy (open arrow), is visible. B. Celiac angiogram obtained before transarterial chemoembolization indicated an area of patchy staining (arrowheads) in the right hepatic lobe due to the presence of arterioportal shunt, as well as various other nodular staining lesions (arrows). C. Precontrast CT obtained two weeks after transarterial chemoembolization shows wedge-shaped retention of iodized oil in the area corresponding to arterioportal shunt (arrowheads). Follow-up CT (not shown) indicated that in contrast to other nodular uptake by tumors, this retention had washed out.

Fig. 6

Arterioportal shunt secondary to hemangioma. A. T2-weighted MRI shows an exophytic hemangioma (arrow) with bright signal intensity in the left lobe of the liver. B. Gadolinium-enhanced dynamic MRI obtained during hepatic arterial phase shows a focal hyperintense area due to arterioportal shunt in adjacent parenchyma (arrows), as well as peripheral nodular enhancement of the hemangioma (arrowheads). C. Further cranial section demonstrates early enhancement of the peripheral portal veins (arrows).

Fig. 7

Arterioportal shunt secondary to hepatocellular carcinoma. A. CT scan obtained during hepatic arteriography shows wedgeshaped hyperperfusion (arrowheads) around the tumor (arrows). B. CT performed during arterial portography shows a perfusion defect at the corresponding area (arrowheads). C. T2-weighted MRI shows a hyperintense area (arrowheads) around the tumor (arrows), which corresponds to the area of arterioportal shunt.

Fig. 8

A 53-year-old man with hepatocellular carcinoma. A. CT scan obtained during the aortic phase shows a 'thread-and-streak' sign at the tumor thrombus in the portal vein (arrowheads). B. Hepatic arterial phase image shows diffuse hepatocellular carcinoma with heterogeneous attenuation in the right lobe invading the right hepatic vein and inferior vena cava (arrowheads). Note the 'thread-and-streak' sign at the tumor thrombus. C. CT scan obtained caudad to figure (B) shows diffuse hepatocellular carcinoma in the right lobe invading the portal vein (arrowheads). The straight border at the left lobe (arrows) does not indicate the tumor margin but appears to be caused by arterioportal shunt. Note that blood flow in the inferior accessory hepatic vein (open arrow) is highly opacified. D. Portal venous phase image shows an area of abnormal hyperattenuation at segment VI (arrowheads). In this case, the shunted flows from the tumor thrombus in the hepatic and portal veins seem to drain into segment VI and then into the inferior accessory hepatic vein.

Fig. 9

Arterioportal shunt secondary to transarterial chemoembolization. A. CT scan obtained during hepatic arterial phase shows peripheral wedge-shaped hyperattenuation caused by arterioportal shunt at the left lobe of the liver (arrowheads). Note the nodular iodized-oil uptake (arrows) inside the hyperattenuating area. B. Portal venous phase image shows that parenchymal enhancement has returned to normal. Note the retracted capsule (arrow) and minimally dilated bile ducts (arrowheads); both findings may indicate the presence of ischemic injury due to repeated transarterial chemoembolization. C. Left hepatic arteriogram reveals wedge-shaped staining and retrograde opacification of the peripheral portal vein in the corresponding area (arrows) and other areas (arrowheads).

Fig. 10

Arterioportal shunt secondary to cholangiocarcinoma. A. CT scan obtained during hepatic arterial phase shows diffuse hyperattenuation at the left lobe of the liver, as well as a large hypoattenuating mass (arrowheads) and dilated bile ducts. B. Portal venous phase image demonstrates that parenchymal enhancement has returned to nearly normal. Note that the left portal vein is encased by the tumor (arrow).

Fig. 11

Nodular-shaped nontumorous arterioportal shunt mimicking hepatic tumor in cirrhotic liver. A. CT scan obtained during hepatic arterial phase shows a nodular hyperattenuating lesion (arrow) in the right lobe of the liver. Note the subtle, tiny portal branch inside the lesion. B. Subsequent hepatic angiogram shows multiple patchy areas of staining in the liver (arrowheads), with early opacification of the portal veins. C. Follow-up CT scan obtained during hepatic arterial phase shows no hyperattenuating lesion in the same area, indicating that the lesion depicted in (A) was a nontumorous arterioportal shunt.

Fig. 12

Tumorous (hepatocellular carcinoma) and nontumorous arterioportal shunt in cirrhotic liver. A, B. CT scans obtained during hepatic arterial phase depict focal hyperattenuating lesions in segment II (arrow in (A)) and segment VI (arrow in (B)). Both lesions are rectangular-shaped and located in subcapsular areas. Note the enhanced peripheral portal vein (arrowheads in (A)) inside the lesion in segment II. C, D. Portal venous phase images show no lesion in segment II, indicating that the lesion depicted in (A) is a nontumorous arterioportal shunt; however, a nodular hypoattenuating lesion with rim enhancement is seen in segment VI (arrow in (D)), indicating hepatocellular carcinoma. Note that the size and shape of the lesion in segment VI differ slightly between the hepatic arterial phase (B) and portal venous phase (D) images, indicating the presence of arterioportal shunt around the tumor.

Fig. 13

Arterioportal shunt secondary to hepatic abscess. A, B. CT scans obtained during hepatic arterial phase show a hepatic abscess (arrow), with wedge-shaped hyperattenuation (arrowheads) in the adjacent parenchyma. C, D. Portal venous phase images depict abscess wall enhancement, and the demarcation of the abscess is clearer than in the hepatic arterial phase image (arrow). Portal venous phase images show that parenchymal enhancement has returned to normal. Note that the wedge-shaped parenchymal hyperattenuation demonstrated by hepatic arterial phase imaging points to the thrombosed hepatic vein (arrowheads).