Comparison of sonographic and CT findings for the identification of renal nodules in dogs and cats.

Ultrasonography (US) and computed tomography (CT) are used to diagnose neoplastic and non-neoplastic focal renal lesions in dogs and cats; however, comparative studies between these two diagnostic tools are lacking. The aim of this retrospective, methods comparison study was to evaluate and compare the performance of US compared to CT in identifying at least one renal nodule in animals with confirmed focal renal lesions. Imaging studies of animals with uni- or bilateral renal nodules smaller than 3 cm that underwent both US and CT and that had a pathologically confirmed diagnosis were reviewed. Animals with renal cysts and infarcts were excluded. Recorded features for both modalities included the following: shape, size, number, localization, margins, renal profile. For CT only, recorded features also included attenuation (HU) and pattern of enhancement.  For US only, recorded features also included echogenicity, echostructure, and rate of visibility. Final diagnosis was obtained by cytology or histopathology. Using CT, lesions were identified in all 39 (100%) kidneys of 18 dogs and seven cats. Most lesions were multiple, cortical, well-defined, iso-attenuating (precontrast), hypo-attenuating, and moderately enhancing (postcontrast). Using US, lesions were identified in 29 of 39 (74%) kidneys. Overall, nine (31%) lesions were poorly visible; 10 (26%) kidneys appeared normal; in 17 (59%) organs, lesions' number was underestimated. Isoechoic, non-protruding lesions were difficult to identify by US. Ultrasonography underestimated renal lesions compared to CT in 59% of the kidneys (P = 0.001). Final diagnoses included metastatic disease (n = 16), infiltration by feline lymphoma (n = 4), primary neoplasia (n = 3), and non-neoplastic benign lesions (n = 2).