In vivo radiographic characteristics associated with the mineral composition of calcium oxalate and struvite lower urinary tract uroliths in cats

Abstract Background Radiography is widely used to diagnose lower urinary tract (LUT) urolithiasis in cats. Non-invasive identification of urolith mineral composition (UMC) is critical for therapy selection but remains challenging, as most data derive from dogs. Hypothesis/Objectives To describe in vivo radiographic features of feline calcium oxalate and struvite LUT uroliths and identify distinguishing characteristics. Animals Sixty-nine cats with LUT uroliths containing ≥70% of calcium oxalate (n = 45) or struvite (n = 24). Methods Retrospective cross-sectional study. Radiographs were evaluated for urolith size, shape, surface, internal architecture, subjective radiopacity, and quantitative radiopacity, assessed using a ratio of urolith-to-L5 vertebra pixel values (UOR). Diagnostic performance of urolith size and UOR was assessed with receiver operating characteristic (ROC) curves, calculating the area under the ROC curve (AUC). Results Struvite uroliths had lower quantitative radiopacity with a UOR cut-off ≤0.78 (AUC = 0.81, P .001; sensitivity: 58%, specificity: 92%). They were larger, with a cut-off value of ≥7.3 mm (AUC = 0.75, P .001; sensitivity: 38%, specificity: 98%), more frequently irregularly shaped, with rough surface and heterogeneous architecture. Urease-positive bacteriuria was present in 43% of struvite uroliths; infected struvite uroliths were significantly larger (median, 9.8 mm; interquartile range IQR, 5.4-13 mm) than sterile ones (median, 4.6 mm; IQR, 2.6-5.4 mm; P = .02). Calcium oxalate uroliths were frequently smaller, more radiopaque, uniform, smooth, and associated with nephroliths. Conclusions and clinical importance In vivo radiographic characteristics aid in differentiating struvite from calcium oxalate LUT uroliths, selecting non-invasive therapy, and reducing unnecessary surgeries.