Which is better for finding renal nodules, CT or US?

VRU 2023 - 64(3) 439-447

December 03, 2023

Background: The article is about a study that compared the performance of ultrasound (US) and computed tomography (CT) in detecting renal nodules in dogs and cats.

Study: The study was a retrospective, methods comparison design that included 25 animals (18 dogs and 7 cats) with focal renal nodules confirmed by cytology or histopathology. The animals underwent both abdominal US and pre- and postcontrast CT within 1 week.

Methods: The US and CT images were reviewed independently by two radiologists who were blinded to the final diagnosis. The number, size, shape, location, margins, and other features of the renal nodules were recorded for both modalities. The visibility of the nodules in US was compared with CT and classified as clearly visible, poorly visible, or not visible. Statistical analysis was performed to evaluate the difference in the number of nodules detected by US and CT and the effects of various factors on the nodules visibility in US.

Results: CT identified renal nodules in all 25 animals and 39 kidneys, whereas US identified nodules in 21 animals and 29 kidneys. US underestimated renal lesions compared to CT in 59% of the kidneys (P = 0.001). The median weight of dogs with visible renal lesions in US was significantly lower than that of dogs with undetected lesions (16.0 kg vs 29.5 kg, P = 0.032). No significant effect of species, sex, kidney side, nodule location, number of nodules, nodule size, nodule shape, and final histologic diagnosis on the nodules visibility in US was found. Isoechoic, non-protruding lesions were difficult to identify by US.

Limitations: The study had some limitations, mainly due to the retrospective nature and the small sample size. Doppler study of the kidney was not available for all cases. Histopathology was available only for two cases and necropsy was not performed to confirm the CT findings. The exclusion of renal lesions bigger than 3 cm might have introduced a bias and under-represented primary cancer.

Conclusions: The study concluded that US failed to diagnose or underestimated the number of inflammatory and neoplastic nodules in a large number of cases compared to CT. Renal nodules were frequently represented by metastases, especially from lung and thyroid carcinomas, supporting the use of CT as an adjunct imaging technique for staging purposes.

Example of a single renal nodule imaged with grey-scale US (A, microconvex probe, 8 MHz), Color Doppler (B) and CT (C, post-contrast, sagittal reformatted CT image, acquired in sternal recumbency, during early venous phase, with soft tissue algorithm, slice thickness 1.25 mm, 120 kV, 250 mA, pitch 0.5). All images modality clearly showed the nodule, with a high flow with Color Doppler and a moderate heterogeneous enhancement in CT. Final diagnosis was a metastasis arising from thyroid carcinoma

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