Detection of nephrocalcinosis using ultrasonography, micro‐computed tomography, and histopathology in cats

Abstract Background Identification of nephrocalcinosis in cats with chronic kidney disease (CKD) is of clinical interest but the ability of ultrasonography to detect nephrocalcinosis is uncertain. Objectives To compare ultrasonography, micro‐computed tomography (μCT) and histopathology for identification of nephrocalcinosis. Animals Twelve kidneys from 7 euthyroid client‐owned cats with CKD. Methods Descriptive study. Renal ultrasonography was performed ante‐mortem for nephrocalcinosis detection. Kidneys were grouped based on nephrocalcinosis: present, suspected, or absent. When cats died, necropsy was performed. Renal tissue was evaluated using μCT for macroscopic nephrocalcinosis, and nephrocalcinosis volume‐to‐kidney tissue ratio (macro‐VN:KT) and sagittal nephrocalcinosis area‐to‐kidney tissue ratio (macro‐AN:KT) were calculated. Each kidney subsequently was bisected longitudinally, formalin‐fixed, and paraffin‐embedded for microscopic nephrocalcinosis assessment using von Kossa and Alizarin red staining with AN:KT (VK‐micro‐AN:KT and AR‐micro‐AN:KT) quantified using ImageJ. Data are presented as median (range). Relationships between macroscopic and microscopic AN:KT were assessed using Spearman's correlation. Results Nephrocalcinosis by ultrasonography was considered to be absent in 3, suspected in 3, and present in 5 kidneys; 1 kidney had nephrolithiasis with nephrocalcinosis. The macro‐VN:KT was 0.001%, 0.001%, and 0.019%, and the macro‐AN:KT was 0.08%, 0.30%, and 1.47%, respectively. Histologically, VK‐micro‐AN:KT was 0.21%, 2.85%, and 4.56%, and AR‐micro‐AN:KT was 1.73%, 5.82%, and 8.90% for kidneys where ultrasonographic macro‐nephrocalcinosis was absent, suspected, or present, respectively. A strong correlation was identified between macroscopic (macro‐AN:KT) and microscopic (VK‐micro‐AN:KT) nephrocalcinosis (rs = 0.76; P = .01). Conclusions and Clinical Importance Ultrasonographically diagnosed nephrocalcinosis correlates well with macroscopic and microscopic nephrocalcinosis at necropsy despite their separation in time.