ULTRASONOGRAPHIC DIAGNOSIS OF PORTOSYSTEMIC SHUNTING IN DOGS AND CATS

This article reviews some of the important physical principles involved in Doppler ultrasound (US) in the context of modern diagnostic US technology. Methods of quantitative Doppler US data analysis used to distinguish normal hemodynamics from disturbed flow conditions are discussed with the aid of numerous examples. Definitions and measurement techniques are presented for determining from Doppler signals such indicators of arterial disease as velocity, volume flow rate, flow impedance, and pulsatility. Spectral analysis and its utility in Doppler signal analysis are described. The various options available on modern Doppler US instrumentation are reviewed, including duplex Doppler techniques and color Doppler flow mapping. Finally, the authors discuss artifacts and pitfalls likely to be encountered in the routine clinical use of Doppler US for diagnostic purposes.

Cases diagnosed with portosystemic shunting between the years 1993 and 2001 were reviewed. Sensitivities of screening tests and abdominal ultrasonographic evaluation for the detection of portosystemic shunting were evaluated. Prognosis for surgically treated shunts was also evaluated. Results indicated that both paired serum bile acids and blood ammonia levels were useful screening tests for portosystemic shunting. However, paired bile acid tests were significantly more sensitive than blood ammonia levels. Overall postoperative mortality rates for extrahepatic shunts and intrahepatic shunts were 8.7% and 20%, respectively. Postoperative mortality rates were slightly higher for animals treated with partial ligation when compared to those treated with ameroid ring placement, although this did not reach statistical significance. Long-term complication rates for animals with single extrahepatic portosystemic shunts treated with complete ligation, ameroid ring placement, and partial ligation alone were 9%, 15.4%, and 42%, respectively. Animals >2 years of age with extrahepatic shunts had almost identical postoperative mortality and long-term complication rates as animals < or = 2 years of age. No animal in this study had paired bile acid samples within the reference range postoperatively, indicating continued abnormal liver function after surgery.