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-VNKT) and sagittal nephrocalcinosis area-to-kidney tissue ratio (macro-ANKT) 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 ANKT (VK-micro-ANKT and AR-micro-ANKT) quantified using ImageJ. Data are presented as median (range). Relationships between macroscopic and microscopic ANKT 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-VNKT was 0.001%, 0.001%, and 0.019%, and the macro-ANKT was 0.08%, 0.30%, and 1.47%, respectively. Histologically, VK-micro-ANKT was 0.21%, 2.85%, and 4.56%, and AR-micro-ANKT 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-ANKT) and microscopic (VK-micro-ANKT) 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.