Canine intrahepatic portosystemic shunts: Interlobar and intralobar classifications

Nicholas D. Walsh, Ian R. Porter, Allison V. Miller, Anthony J. Fischetti, Soon Hon Cheong, Peter V. Scrivani

Background: Intrahepatic portosystemic shunts (IPSS) are vascular anomalies that bypass the liver and cause clinical signs such as hepatic encephalopathy, stunted growth, and abnormal blood tests. IPSS are classified as intrahepatic or extrahepatic, and further categorized by their location and connection to the portal and systemic venous systems. The authors aimed to review normal canine liver anatomy and categorize IPSS findings using CT angiography (CTA) by using interlobar and intralobar descriptions.

Study: The study consisted of two parts: a prospective anatomic study and a retrospective multi-institutional case series. The anatomic study included a literature review, specimen examination, and CT images of normal canine livers to illustrate the normal ductus venosus (DV) and its eponymous fissure. The case series included 56 dogs with a single IPSS that underwent CTA at Cornell University or the Schwarzman Animal Medical Center. The authors evaluated the CTA images and classified each IPSS as left, central, or right divisional, and as interlobar or intralobar. They also recorded the afferent and efferent flows of each IPSS and the presence of other anomalies.

Methods: The authors used different CT scanners and contrast agents at the two institutions, but followed similar protocols for image acquisition and reconstruction. They used bolus tracking software to trigger image acquisition when the aorta reached a certain threshold of contrast enhancement. They also acquired venous phase images after a delay. They used a soft-tissue algorithm and window for image display and analysis. They used medical imaging processing software to create volume-rendered models of the specimens. They used consensus between two ACVR-certified radiologists to classify the IPSS and record the data. They used MedCalc software to summarize the demographic data and report the frequency of CTA observations by shunt types.

Results: The normal canine DV passes through the fissure for ligamentum venosum between the papillary process and the left lateral lobe, and then turns right to join the left side of the CVC. They also found that 43% of the dogs with IPSS had an interlobar shunt, which was typically near the median plane, remained interlobar throughout its course, and was nearly always craniodorsal to the porta hepatis. They distinguished four types of interlobar shunts: patent DV, left interlobar, right interlobar, and ventral interlobar. They also found that 57% of the dogs with IPSS had an intralobar shunt, which was mostly in the right lateral lobe or caudate process, and originated from the right portal branch in most cases. They also observed some other anomalies, such as segmental aplasia of the CVC, acquired portosystemic shunts, and abnormal liver lobation.

Limitations: The authors acknowledged several limitations of their study, such as the small sample size, the retrospective design, the lack of independent confirmation of the shunt location, the variability of image acquisition and reconstruction parameters, and the influence of patient variables on the results. They also noted that their assessment might not apply to cases with multiple IPSS or collaterals.

Conclusions: The authors concluded that canine congenital IPSS can be classified as interlobar or intralobar based on their location within or through a liver lobe. They also proposed that this classification might increase the reliability and validity of CTA descriptions of IPSS, improve communication between radiologists and other healthcare professionals, and facilitate therapeutic planning, especially for intravascular coil embolization or liver lobectomy. They suggested further research to evaluate the efficacy of these treatments for different types of IPSS.

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