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 vivo studies.

Objectives

To describe in 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 ≥ 70% calcium oxalate (n = 109), struvite (n = 58), or cystine (n = 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 mm; IQR: 8.1–25.8 mm) with a cut-off of ≥ 11 mm (AUC = 0.82, p < 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 ≤ 0.83 (AUC = 0.81, p < 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.