Simple SummaryDogs may be born with an abnormal vessel that bypasses their liver (congenital portosystemic shunt), causing a variety of clinical signs due to toxins building up in the bloodstream. Closing the abnormal vessel completely in a one-stage surgery is ideal but cannot always be tolerated, in which case partial closure with a material that induces ongoing shunt narrowing by inflammation may be chosen. Some dogs receive a second surgery to achieve full closure of the abnormal vessel if ongoing inflammation around the shunt has not managed to produce full shunt closure. There are inaccuracies reported with trying to assess if the abnormal vessel has progressed to full closure using regular ultrasound and computed tomography (CT) imaging to follow up after surgery. The objective of this study was to compare intra-operative X-ray findings (portovenogram) using a dye (contrast) injected directly into the abnormal vessel at a routine second surgery to accurately determine whether different methods of narrowing the shunt achieved full shunt closure over time. Twenty-four dogs were enrolled, 12 received partial polypropylene suture ligation, and 12 received partial thin film band shunt attenuation. Intra-operative portovenography three months after the first surgery demonstrated that nine dogs (75%) that had their shunt narrowed with a thin film band had achieved complete shunt closure versus two dogs (16.7%) that had their shunt narrowed with polypropylene suture. Multiple acquired shunts, which are not congenital but develop in response to excessive pressure within the liver’s circulation (due to narrowing or closure of the single congenital shunt), developed in two dogs receiving thin film band attenuation of their congenital shunt.AbstractThe objective was to conduct a prospective, randomized study to compare mesenteric portovenogram findings following partial polypropylene suture versus thin film band extrahepatic portosystemic shunt attenuation in dogs. Dogs with extrahepatic portosystemic shunts that could not tolerate complete acute shunt closure received a partial attenuation with either a polypropylene suture or synthetic polymer thin film band. At a routine second surgery three months after shunt patency, missed shunt branches and/or development of multiple acquired shunts were assessed using intra-operative mesenteric portovenography. Twenty-four dogs were enrolled, 12 received partial polypropylene suture ligation, and 12 received partial thin film band shunt attenuation. Intra-operative mesenteric portovenography three months later demonstrated that nine dogs (75%) in the thin film band group had achieved complete shunt closure versus two dogs (16.7%) in the polypropylene suture group, which was significantly different (p= 0.004). No dogs in the polypropylene suture group and two dogs (16.7%) in the thin film band group developed multiple acquired shunts. This is the first study directly comparing follow-up intra-operative mesenteric portovenography imaging findings between two methods of partial portosystemic shunt attenuation in dogs. The study provides accurate information on the rates of complete anatomical shunt closure and development of multiple acquired shunts following partial shunt attenuation with either synthetic polymer thin film band or polypropylene suture.