Resumen de Analysis of the relationship of extrahepatic portosystemic shunt morphology with clinical variables in dogs: 53 cases (2009–2012)
Objective—To investigate differences in clinical variables among dogs with extrahepatic portosystemic shunts (EHPSSs) of various morphologies.
Design—Retrospective case series.
Animals—53 dogs with EHPSSs.
Procedures—Medical records of dogs undergoing preoperative CT angiography of an EHPSS over a 3-year period were reviewed. Analysis was performed to investigate relationships of clinical variables with shunt morphology. Morphologies were analyzed individually as well as in several groups.
Results—Shunt morphologies included 10 splenocaval, 9 splenophrenic, 11 splenoazygos, 10 right gastric-caval, 12 right gastric-caval with a caudal loop, and 1 right gastric-azygos with a caudal loop. Several biochemical variables associated with EHPSS were lowest in dogs with splenocaval shunts. Preoperative clinical signs were more common in dogs that had shunts with vena caval than right azygos vein insertion (36/41 [88%] vs 7/12 [58%]) and insertion caudal to the liver than diaphragmatic insertion (29/32 [91%] vs 14/21 [67%]). Neurologic signs were more common when shunts inserted into the vena cava caudal to the liver than in other locations (21/32 [66%] vs 6/21 [29%]) and were most frequent with splenocaval shunts. Urinary tract signs were more common when shunts had right gastric vein origin than gastrosplenic vein origin (14/23 [61%] vs 10/30 [33%]).
Conclusions and Clinical Relevance—Splenocaval shunts caused more clinical abnormalities than did other shunt morphologies. Results suggested that dogs with shunt insertion in the caudal vena cava, especially caudal to the liver, were most likely to have clinical signs.
Congenital EHPSSs are anomalous vessels that result from defective development of the hepatic vasculature. Extrahepatic PSSs represent an inappropriate functional connection between the embryonic cardinal and vitelline venous systems.1 After birth of an animal, EHPSSs, similar to intrahepatic shunts and other hepatic vascular anomalies, allow venous blood drained by the portal system to bypass the liver and enter directly into the systemic circulation. The resultant decrease in the delivery of trophic factors to the liver and release of substances typically metabolized by the liver into the systemic circulation cause a pattern of clinical and laboratory abnormalities that have been characterized.2–4 Patients with EHPSSs are most commonly small- or toy-breed dogs. Affected dogs are often evaluated because of a suspected EHPSS before they reach 2 years of age, although some patients do not develop clinical signs until they are much older.5,6 Clinical signs associated with PSSs may range from mild to severe. Some patients have a general failure to thrive, whereas others have more specific clinical signs. Owner-reported abnormalities most commonly relate to 3 body systems: the CNS, gastrointestinal tract, and urinary tract. A subset of patients with congenital EHPSSs has no overt clinical signs, and shunts are discovered only when abnormalities are detected during laboratory testing for routine health screenings or elective surgical procedures. Characteristic clinicopathologic findings associated with EHPSSs include microcytosis (with or without anemia), hypoalbuminemia, low BUN concentration, hypocholesterolemia, hypoglycemia, mild increase in ALT and ALP activities, poorly concentrated urine, and ammonium biurate crystalluria. In cases in which a PSS is suspected, findings of high blood ammonia or SBA concentrations serve as additional evidence of a PSS.
Within the category of EHPSS, a variety of common shunt morphologies are recognized. Historically, EHPSSs were classified simply as portocaval (inserting on the caudal vena cava) or portoazygos (inserting on the azygos vein). Common patterns of vessel origin and insertion have been described,1,7 but the increased use of CTA in veterinary medicine has helped to more specifically characterize shunt morphology.2–4,8 A link between shunt morphology and degree of clinical illness has long been suspected2,5,6 and has been suggested in several studies.2,9–12 In particular, patients with portoazygos or portophrenic (inserting on a phrenic vein that drains into the vena cava at a point cranial to the liver) shunts developed clinical signs when they were much older9–11 and, anecdotally, were believed to develop fewer clinical signs than patients with portocaval shunts.2,12 However, those studies relied on intraoperative visual identification of anatomic structures or less precise imaging modalities such as ultrasonography, nuclear scintigraphy, or portovenography to determine shunt origin and insertion. Although these diagnostic methods have been described in the context of shunt diagnosis, they have limitations in terms of characterization of shunt morphology. Intraoperative visual identification has long been considered the criterion-referenced standard for diagnosis of shunt morphology, but the recognition of portophrenic shunts as a common EHPSS morphology and increasing reports of multiple10,13–17 or complex8 congenital shunts cast doubt on the accuracy of the diagnosis for intraoperative visual identification. Use of CTA during the preoperative evaluation of dogs with EHPSSs provides an opportunity to critically evaluate the effect of shunt morphology on other variables by ensuring a consistent, accurate diagnosis of shunt morphology.
The purpose of the study reported here was to determine whether a relationship exists between EHPSS morphology (as determined by use of CTA) and patient signalment, clinical signs, laboratory abnormalities, or short-term survival rate. On the basis of findings for previous studies,9–12,18,19 we suspected that EHPSS morphology would have an influence on the clinical variables examined. However, we tested the null hypothesis that clinical variables would not differ among various EHPSS morphologies.
