Disappearance of a spontaneous intrahepatic portosystemic shunt managed by hepatic vein closure: Why?

Abstract

Introduction

Spontaneous intrahepatic portosystemic shunt (PSS) is uncommon. A few cases have been reported with its disappearance after outflow occlusion. It is unclear why it had disappeared, and the mechanism is closely related to the pathophysiology of PSS. The portal circulation is a ‘flow’ and governed by Ohm’s law (Flow=Pressure/Resistance). This can be explained through simulation using an electric circuit, which is also a flow system.

Case description

A 62-year old woman visited with hepatic encephalopathy. She had no history of chronic liver disease or liver trauma. Imaging studies revealed an intrahepatic aneurysmal PSS in Couinaud’s segment 6, formed between the posterior branch of right portal vein and the right inferior hepatic vein. She was managed by laparoscopic right inferior hepatic vein closure using an autostapling device. Her encephalopathic symptoms improved immediately after the operation, and she was discharged uneventfully. At her 8 month follow-up, she was symptom-free and her PSS disappeared entirely.

Results and Conclusions

The basic configuration of splanchnic circulation is essentially two resistors connected in series; the mesenteric vascular resistance and the portal vascular resistance. It is a pressure divider between the aortic pressure and systemic venous pressure. In turn, the portal vascular resistance can be seen as two resistors connected in parallel; the hepatic vascular resistance and the PSS resistance. A PSS means the shunt flow above zero, and according to Ohm’s law, there are two ways for the PSS to be formed. In one condition, the portal pressure increases sufficiently high and a PSS begins to form at a fixed shunt resistance. Once the shunt channel is established, portal pressure will decrease until equilibrium is reached between the portal pressure and the shunt flow. A clinical example is liver cirrhosis. In this condition, PSS will persist even if the outflow is occluded. In the other condition, the shunt resistance can decrease at a fixed portal pressure, such as an aneurysmal dilatation of PSS. In this case, PSS will disappear after outflow occlusion, because the shunt flow becomes zero. The puzzling phenomenon of the disappearance of PSS in our case can be easily explained by simulation using an electric circuit theory.

Take home message

Blood flow is similar to an electric current and is governed by Ohm’s law. By simulating splanchnic blood flow with an electric circuit, we can easily understand the underlying pathophysiology of many seemingly curious phenomena.