In Vivo Radiographic Characteristics Associated With the Mineral Composition of Calcium Oxalate, Struvite, and Cystine Lower Urinary Tract Uroliths in Dogs.

Abstract

BACKGROUND: Identifying urolith mineral composition (UMC) is crucial for treatment and prevention; however, current data rely on macroscopic or ex&#xa0;vivo studies. OBJECTIVES: To describe in&#xa0;vivo radiographic characteristics of canine lower urinary tract (LUT) uroliths and identify discriminating radiographic features among UMC types. ANIMALS: Two hundred and two dogs with LUT uroliths composed of &#x2265;&#x2009;70% calcium oxalate (n&#x2009;=&#x2009;109), struvite (n&#x2009;=&#x2009;58), or cystine (n&#x2009;=&#x2009;35). METHODS: Retrospective cross-sectional study. Radiographs were evaluated for urolith size, shape, surface, borders, internal architecture, and quantitative radiopacity, and also assessed using a ratio of urolith-to-L5 vertebra pixel values (UOR). The diagnostic performance of urolith size and UOR was assessed with receiver operating characteristics (ROC) curves, calculating the area under the ROC curve (AUC). RESULTS: Calcium oxalate uroliths were often highly radiopaque, associated with concurrent nephroliths, had unique shapes such as bosselated or spiculated, and less commonly ovoid. Struvite uroliths were larger (median: 15&#x2009;mm; IQR: 8.1-25.8&#x2009;mm) with a cut-off of &#x2265;&#x2009;11&#x2009;mm (AUC&#x2009;=&#x2009;0.82, p&#x2009;<&#x2009;0.001; specificity: 91%, sensitivity: 67%) and were associated with pyramidal shapes or solitary cystoliths. Cystine uroliths had lower radiopacity (median UOR: 0.71; IQR: 0.63-0.80), with a cut-off of UOR &#x2264;&#x2009;0.83 (AUC&#x2009;=&#x2009;0.81, p&#x2009;<&#x2009;0.001; specificity: 67%, sensitivity: 84%). CONCLUSIONS AND CLINICAL IMPORTANCE: In vivo radiographic characteristics such as size, shape, and radiopacity can help differentiate LUT mineral compositions, enabling non-invasive diagnosis and guiding treatment.