Ultrasound Morphology of Presumed Normal Anal Sacs in Dogs and Cats

Ultrasonographic evaluation of canine and feline anal sacs is a practical promising modality to identify anal sac disease. However, limited data are available about normal ultrasound morphology of the anal sacs. This study describes the ultrasound morphology of presumed normal anal sacs in a larger sample of client-owned dogs and cats. A single-institutional prospective cross-sectional descriptive study was performed, and 137 dogs and 131 cats were included. The most common ultrasound features of the evaluated anal sacs in the dorsal plane were oval shape (99.3% of dogs and 98.5% of cats) and bilaterally similar content (94.2% of dogs and 95.4% of cats), mostly hypoechoic with diffusely hyperechoic points or unformed echogenic material (42.6% of dogs and 44% of cats). Gas in the lumen of the anal sac was detected in two dogs and mineralization in one dog. There was a statistically significant positive correlation between body weight and the size of anal sacs in dogs ≤15 kg and cats and a correlation between age and the size of anal sacs in cats. This simple method provides additional clinically significant information in detecting abnormal findings in asymptomatic patients and could contribute to the early detection of anal sac disease.