Clinical Connections  –  Autumn 2020

A new descriptive study has determined important variations in the classification of congenital intrahepatic portosystemic shunts (IHPSS) in dogs. These findings are an important step in not only the diagnosis but surgical method and recommended treatments.

The research, conducted at the RVC, and in collaboration with the School of Veterinary Medicine in Davis, the University of Tennessee Small Animal Hospital and the College of Veterinary Medicine in Georgia, sought to analyse and provide exact characterisation of IHPSS, which has historically lacked a complete anatomical overview, making diagnosis and treatment challenging.

Traditionally classified as right, left or central divisional, this cross-sectional study hypothesised that there would be important variation to this classification and therefore assessed for IHPSS type, insertion and the relationship of the insertion to the primary hepatic veins.

The newly introduced classification system for intrahepatic portosystemic shunts determines the shunt type based on the insertion of the abnormal connection via an existing hepatic vein. Schematic drawings and corresponding CT angiography images show examples of subtypes for single right divisional intrahepatic shunts: connecting to the systemic venous circulation via the right lateral (A,B) and caudate (C,D) hepatic vein respectively.
Abbreviations: PV, portal vein; RPB, right portal branch; LPB, left portal branch; CVC, caudal vena cava; LHV, left hepatic vein; CHV, central hepatic vein; DRM, dorsal right medial hepatic vein; RL, right lateral lobar vein; Ca, caudate lobar vein

As part of the study, 90 dogs, aged three months to 13 years, which were diagnosed with an intrahepatic shunt via computed tomographic angiography were analysed. In 92 per cent of the evaluated IHPSS, a connection to an existing hepatic vein or phrenic vein was seen as hypothesised. Only eight per cent of the IHPSS connected directly to the caudal vena cava, the main systemic vein that returns blood to the heart, which was previously thought to be the main route of these anomalous connections.

While the previously defined classification of left, right and central divisional shunt types remains valid, the results show that further subclassifications can be reliably defined based on the hepatic veins with which the shunting vessel communicates, which can, in turn, determine if surgical correction of the defect is possible, and optimally plan for an efficient surgical approach in these aesthetically challenging cases.

Dr Randi Drees, Associate Professor in Veterinary Diagnostic Imaging, said: “The newly introduced classification of the IHPSS based on the individual hepatic venous structure that it inserts through will likely be more reliable than the historical global classification system, as it relies on given anatomical structures that can be investigated with advanced imaging modalities such as angiographic computed tomography, illustrating the deficiencies of the traditional approach.

“We expect the results of this study to change the way radiologists report these birth defects, and therefore optimise communication with the surgeons, improving overall patient care."

Research reference

Plested MJ, Zwingenberger AL, Brockman DJ, et al. Canine intrahepatic portosystemic shunt insertion into the systemic circulation is commonly through primary hepatic veins as assessed with CT angiography. VetRadiol Ultrasound. 2020;1–12.

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