Nontumorous arterioportal shunts in the liver: CT and MRI findings considering mechanisms and fate

Abstract

The intrahepatic non-tumorous arterioportal shunt (APS) is one of the important causes of transient hepatic enhancement differences (THED) on dynamic CT or MRI. Most small APSs are located in the peripheral portion of the liver. Because of the parenchymal distortion in the advanced cirrhotic liver, many small APSs tend to show an amorphous or nodular appearance, making them difficult to distinguish from hypervascular tumors. In addition to the use of dynamic CT or MRI, iso-attenuation densities or iso-intensities on pre-contrast and equilibrium phases, MRI using a liver-specific contrast agent can be useful to characterize the hypervascular pseudolesions. Because there is no difference in water diffusion in the hepatic parenchyma in the region of the APS, diffusion-weighted MRI also has great potential to distinguish non-tumorous shunts from true focal lesions. Larger (>2 cm) APSs of direct arterio-portal venous fistulas from extrinsic insults show typical subcapsular wedge-like THEDs that are only temporarily depicted several months after the traumatic event; most of these THEDs gradually decrease in size or vanish completely. By understanding the nature of non-tumorous APSs, radiologists will be able to provide a more accurate assessment of many THEDs during daily interpretations of CT or MR images of the liver.

Follow-Up of Known Carcinoid Liver Metastases: Is Respiratory-Gated T₂ Fast Spin-Echo Enough?

“…30% of patients had the most lesions noted on the noncontrast phase and 30% had the most lesions detected on the hepatic arterial phase than on any other phase; moreover, in 6% (2/31) of the patients, hepatic lesions were seen exclusively on the hepatic arterial phase. Even though it has been reported that most hypervascular metastases are seen on the arterial phase of contrast, it is difficult to determine whether the hypervascular lesions represent true metastases or small transient hepatic arterial perfusion abnormalities caused by arterial portal venous shunting [6,13]. …”

Recent Advances in the Imaging Diagnosis of Hepatocellular Carcinoma: Value of Gadoxetic Acid-Enhanced MRI

“…As liver cirrhosis progresses, APS via the trans-sinusoidal route can increasingly occur, which is thought to be related to cirrhosis-induced sinusoidal capillarization and obliteration of hepatic venules [82]. In addition, although APS are typically seen as subcapsular wedge-or triangular-shaped transient parenchymal enhancements on the HAP, APS in the cirrhotic liver tend to show a centrally located, round or oval appearance more frequently than those in the non-cirrhotic liver due to the architectural distortion of the background hepatic parenchyma, making the differentiation from HCCs difficult [83]. As a misdiagnosis of hypervascular pseudolesions as HCCs can lead to unnecessary treatment, the differentiation between these two disease entities is of importance in clinical practice.…”

Diagnostic imaging modalities

“…In patients with cirrhosis, the arterioportal shunt is usually found on the arterial phase of a CT scan. The mechanism underlying such an arterioportal shunt is not clear, but it is thought that distortion and capillarization of the hepatic sinusoid disturbs hepatic venular flow and increases intrahepatic vascular resistance, resulting in the arterial blood flow regurgitating to the PV via the arterioportal shunt [75]. Although the arterioportal shunt has minimal clinical significance, it can be mistaken for a small HCC on the arterial phase of a CT scan.…”