Histopathological changes associated with congenital portosystemic shunts (CPSS) are poorly reported in cats. This study describes these changes in cats with CPSS at initial and repeat surgery following partial CPSS attenuation. We hypothesised that histopathological changes would improve following partial CPSS attenuation and would correlate with changes on portovenography.

The medical records, portovenograms and liver biopsies from cats treated surgically for CPSS between May 2000 and May 2011 were reviewed. Cats were treated with suture attenuation of the shunt. A second surgery was performed in most cats that could not tolerate full attenuation. Liver biopsies were graded by three blinded reviewers for histopathological features characteristic of CPSS. Portal vasculature at first and second surgery was graded based on portovenogram findings. Statistical significance was set at 5%.

Forty CPSS cats (34 extrahepatic, 6 intrahepatic) and four control cats were included. Fifteen cats tolerated complete attenuation at first surgery. There was no significant difference in degree of attenuation for age or type of shunt. 19/25 cats undergoing partial attenuation at first surgery had a second surgery. Liver biopsies were available at second surgery from 14 cats and at post mortem from 2 cats that died of unrelated causes.

Forty CPSS cats had characteristic histopathological lesions; portal vein hypoplasia (n = 40), arteriole hyperplasia (n = 40), hepatocyte vacuolation (n = 20) or steatosis (n = 12), portal fibrosis (n = 17), biliary hyperplasia (n = 8) and haemosiderin accumulation (n = 2). Control cats did not have these changes. There was no significant difference in histopathological features between first and second surgery. Cats with steatosis were significantly older than cats without (p = 0.001). Fibrosis and biliary hyperplasia were significantly correlated at first surgery (p = 0.038). No histopathological feature was significantly associated with shunt type, degree of attenuation or portovenogram grade.

There was a significant increase in pre (p = 0.001) and post (p = 0.039) attenuation portovenogram grade from first to second surgery.

This study indicates that histopathological findings in cats with CPSS are similar to those previously described for dogs. Despite improvement in hepatic portal vasculature (on portovenography) following partial attenuation there was no detectable change in histopathological features, suggesting that improvements in portal flow and hepatic perfusion are difficult to detect at the microscopic level. These data suggest that microscopic grading of liver biopsies from cats with CPSS is useful for diagnostic purposes but not a good predictor of the ability to tolerate full attenuation.