The portal vein is a very important blood vessel in which all nutrient- and toxin-rich blood is collected that comes from the gastro-intestinal organs. The portal vein drains into the liver who detoxifies the blood before it enters the systemic circulation (Figure 1). A portosystemic shunt is an anomalous vein that allows portal blood to enter the systemic circulation without first passing through the liver (Figure 2). This is a congenital problem widely described in dogs. Abdominal ultrasound and/or computed tomography are the medical imaging techniques of choice to confirm the presence and type of portosystemic shunt. They are interpreted in a rather static way, not revealing any information on the hemodynamics.
Figure 1. The normal portal vasculature and normal hepatopetal portal blood flow (blood flow towards the liver) (modified from Bezuidenhout 2013)
Figure 2. The portal vasculature in the presence of a portosystemic shunt and two possibilities of hepatofugal portal blood flow (blood flow away from the liver)
Gradual attenuation of the shunt is intended to redirect the blood through the portal branches, which are often hypoplastic and thus need time to adapt to the increased blood flow. The surgical approaches currently used result in incomplete closure of the shunt in 15-30% of the patients. Some of the dogs with a partially attenuated congenital portosystemic shunt have excellent clinical outcomes, whereas others have poor outcomes.
It has been hypothesized that both the blood flow direction (hepatopetal versus hepatofugal) in the segment of the portal vein cranial to the origin of the shunt as well as in the portosystemic shunt adjacent to the portal vein might indicate whether re-operation to close the portosystemic shunt completely should be advised or not in dogs with a patent portosystemic shunt after the first surgery.
The overall objective of this master thesis project is to gain fundamental insight into the direction of the blood flow within the tributaries of the portal system in dogs with a congenital portosystemic shunt. It currently remains unclear whether the goal of shunt attenuation should really be a complete absence of shunting to obtain clinical success in all dogs.
In this thesis, computational fluid dynamics (CFD) modeling will be used to simulate the hemodynamics and assess the blood flow direction through the shunting vessel and the portal tributaries. This information would be helpful to better understand the direction of blood flow in the portal system of dogs with a portosystemic shunt. As an input for the models, patient-specific imaging datasets of dogs will be used (see Fig. 3 for an example).
In addition, computer modelling would greatly help to understand the hemodynamic changes in the portal system of dogs with a patent portosystemic shunt and provide a rationale to advise a second surgery or not.
Figure 3. Preliminary CFD calculation of dog-specific case with a portosystemic shunt showing the resulting pressure profile