Study questions CT liver size as a marker for canine PHPV

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A new study in the American Journal of Veterinary Research challenges a common assumption about canine primary hypoplasia of the portal vein: dogs with histopathologic findings compatible with PHPV did not have detectably lower CT-derived liver volume than dogs without liver disease. The paper focused on CT-derived liver volume and noncontrast attenuation variables, asking whether liver size on CT could help distinguish affected dogs from healthy controls. (acvr-website.s3.amazonaws.com)

That question matters because PHPV has long occupied a gray zone in small animal hepatology. The condition is a congenital microscopic abnormality of the intrahepatic portal vasculature, and the World Small Animal Veterinary Association moved away from the older “microvascular dysplasia” terminology in favor of PHPV. Diagnosis generally depends on liver histopathology together with imaging, such as CT angiography, to rule out macroscopic portosystemic shunts, thrombosis, or other causes of reduced portal perfusion. (frontiersin.org)

The new AJVR article builds on earlier work from the same investigators. In an American College of Veterinary Radiology 2023 abstract, the team reported CT hepatic volumetry in 26 dogs with confirmed PHPV. Toy Poodles were the most common breed, the mean age was 3.7 years, and the mean body weight was 3.9 kg. That abstract reported a mean normalized liver volume of 26.5 cm3/kg, with no significant correlation between normalized liver volume and age or body weight, and concluded that liver volume in dogs with PHPV appeared similar to published values for dogs without liver disease. (acvr-website.s3.amazonaws.com)

That finding is notable because reduced liver size is often part of the mental model clinicians bring to portal vascular disorders. In congenital portosystemic shunts, for example, liver hypoplasia is well recognized, and CT volumetry studies in shunt patients have documented variation in microhepatia by shunt type and body size. By contrast, the PHPV data suggest that diffuse whole-liver volume loss may not be a reliable imaging hallmark, even if regional changes or other vascular abnormalities can still occur in individual cases. (pubmed.ncbi.nlm.nih.gov)

Published background on PHPV helps explain why that distinction matters. A 2017 retrospective study of 48 canine cases found PHPV often presented with increased liver enzymes discovered on routine exams or preoperative bloodwork, and it emphasized that definitive diagnosis still rests on biopsy-based pathology in context. Review articles likewise describe PHPV as one of the two most common congenital hepatic vascular anomalies in dogs alongside congenital portosystemic shunts, but one that can be harder to pin down because imaging may be used more to exclude other diseases than to confirm PHPV directly. (pmc.ncbi.nlm.nih.gov)

Why it matters: For veterinarians, the clinical message is restraint in interpretation. If CT shows a liver that is not obviously small, that does not appear to meaningfully lower the odds of PHPV. In practice, that means CT liver size should probably be treated as one data point, not a rule-out test. Workups for suspected PHPV still need to integrate clinicopathologic findings, bile acids or ammonia when indicated, vascular imaging to assess for shunts or portal abnormalities, and, when appropriate, liver biopsy. The study may be especially useful in referral settings where CT is already part of the diagnostic pathway and there is a temptation to overread liver size as reassuring. (pmc.ncbi.nlm.nih.gov)

No outside expert commentary specific to the new AJVR paper was readily available in the sources reviewed, but the broader literature points in the same direction: PHPV is heterogeneous, terminology and classification have evolved, and imaging findings do not always map neatly onto histopathology. That makes studies like this useful not because they offer a single new diagnostic marker, but because they clarify which assumptions may not hold up under measurement. (frontiersin.org)

What to watch: The next step is whether larger, controlled studies can identify more discriminating CT markers, including attenuation patterns, portal vein measurements, or lobe-level changes, and whether those imaging findings correlate with severity, portal hypertension status, or long-term outcomes in dogs with PHPV. (acvr-website.s3.amazonaws.com)