Background

Congenital portosystemic shunts (PSSs) in cats are vascular anomalies that allow portal blood to bypass hepatic circulation, with surgical attenuation being the treatment of choice. Current diagnostic tools such as scintigraphy have limitations, including poor reproducibility and inconsistencies in predicting surgical outcomes. This study investigated the clinical utility of computed tomography perfusion (CTP) to measure shunt fraction (SF) in cats, offering a potentially more accurate and repeatable method to assess surgical success and prognosis.

Methods

This prospective case study included eight client-owned cats with confirmed PSSs, who underwent surgical treatment between April 2016 and August 2019. CTP-derived SF was measured at three timepoints: preoperatively (first period), postoperative day 14 (second period), and postoperative day 75 (third period). Shunt types, surgical procedures (partial ligation or ameroid constrictor placement), and prognoses were recorded. SF was calculated using dynamic CT imaging, and statistical comparisons were made across timepoints and clinical subgroups.

Results

The median SF significantly decreased over time from the first to the third period (from 89.3% to 16.1%, P = .008). Cats with left gastrophrenic (LGP) shunts showed particularly significant SF reductions. Ameroid constrictor placement consistently resulted in lower SF values over time, while partial ligation had more variable outcomes. Cats with a good prognosis had significantly lower SFs by the third period compared to those with a guarded prognosis. Notably, in some guarded cases, SF remained unchanged or even increased postoperatively, indicating poor surgical response.

Limitations

The primary limitation was the small sample size (n=8), which restricted statistical power and generalizability. Additionally, the CTP protocol was adapted from canine studies, potentially affecting accuracy in cats. In cases where the portal vein was not visualized postoperatively, SF defaulted to 100%, introducing measurement bias.

Conclusions

CTP-derived SF is a feasible and informative tool for evaluating surgical outcomes in feline PSS cases. Reduction in SF postoperatively was associated with favorable prognosis, especially in cats with LGP shunts or those treated with ameroid constrictors. These findings support the potential of CTP in improving diagnostic precision and guiding postoperative management of feline PSSs.