Classify your intrahepatic shunt....

Canine Intrahepatic Portosystemic Shunt Insertion into the Systemic Circulation Is Commonly Through Primary Hepatic Veins as Assessed with CT Angiography

Mark J. Plested, Allison L. Zwingenberger, Daniel J. Brockman, Silke Hecht, Scott Secrest, William T.N. Culp, Randi Drees.

Background
Intrahepatic portosystemic shunts (IHPSS) are congenital vascular anomalies in dogs that allow portal blood to bypass the liver. Traditionally, IHPSS are classified as right, left, or central divisional based on their anatomic course, but little is known about the specific insertion sites of these shunts into the systemic circulation. This study aimed to describe the morphology of IHPSS using computed tomography angiography (CTA) and assess their relationship with primary hepatic veins, hypothesizing that most IHPSS insert via these veins rather than directly into the caudal vena cava.

Methods
A retrospective, multicenter study was conducted using CTA scans from 90 dogs diagnosed with IHPSS at four veterinary referral centers. Shunts were categorized as right, left, or central divisional based on their origin from the portal vein and their course through the liver. The insertion site into the systemic circulation was recorded, noting whether the shunt drained into a primary hepatic vein, a phrenic vein, or directly into the caudal vena cava. Statistical analyses were performed to assess associations between shunt type and patient characteristics such as breed, age, and weight.

Results
The majority of IHPSS (92%) drained into a primary hepatic vein or phrenic vein, rather than directly into the caudal vena cava. Right divisional IHPSS (44%) most commonly inserted into the right lateral hepatic vein or the caudate hepatic vein. Left divisional IHPSS (33%) inserted into the left hepatic vein or left phrenic vein. Central divisional IHPSS (13%) inserted into the quadrate, central, or dorsal right medial hepatic veins. A subset of IHPSS (9%) had multiple insertion sites. Labrador Retrievers were more likely to have left divisional IHPSS, but no associations were found between shunt type and other demographic factors.

Limitations
The study was limited by its retrospective nature and variability in CTA protocols among institutions. Some small-caliber vessels may have been missed due to differences in scan resolution and contrast timing. Additionally, surgical confirmation was not available for all cases, and the impact of IHPSS morphology on surgical outcomes was not assessed.

Conclusions
CTA findings suggest that IHPSS commonly insert into primary hepatic veins rather than directly into the caudal vena cava. This refinement in classification may aid in preoperative planning, particularly for surgical or interventional occlusion techniques. Further studies are needed to assess how these anatomical variations influence surgical success and long-term outcomes in affected dogs.

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