Association of Kidney Cysts With Progressive CKD After Radical Nephrectomy

RATIONALE & OBJECTIVE:Simple kidney cysts are common and usually considered of limited clinical relevance. They are associated with older age and lower glomerular filtration rate (GFR), but little is known of their association with progressive chronic kidney disease (CKD) which was the focus of this study. STUDY DESIGN:Observational cohort study. SETTING & PARTICIPANTS:Patients with pre-surgical CT or MRI imaging who underwent a radical nephrectomy for a tumor. We reviewed the retained kidney images to characterize parenchymal cysts at least 5 mm in diameter according to size and location. EXPOSURES:Parenchymal cysts at least 5 mm in diameter in the retained kidney. Cyst characteristics were correlated with microstructural findings on kidney histology. OUTCOMES:Progressive CKD defined by dialysis, kidney transplantation, a sustained >40% decline in eGFR, or an eGFR <10 ml/min/1.73m2 that was at least 5 ml/min/1.73m2 below the post-nephrectomy baseline for at least 3 months. ANALYTICAL APPROACH:Cox models assessed the risk of progressive CKD. Models adjusted for baseline age, sex, body mass index, hypertension, diabetes, eGFR, proteinuria, and tumor volume. Non-parametric Spearman's correlations were used to examine the association of the number and size of the cysts with clinical characteristics, kidney function, and kidney volumes. RESULTS:There were 1195 patients with 50 progressive CKD events over a median 4.4 years of follow-up. On baseline imaging, 37% had at least one cyst, 34% had at least one cortical cyst, and 8.3% had at least one medullary cyst. A higher number of cysts was associated with progressive CKD and was modestly correlated with larger nephrons and more nephrosclerosis on kidney histology. The number and size of medullary cysts was more strongly associated with progressive CKD than the number and size of cortical cysts. LIMITATIONS:Patients who undergo a radical nephrectomy may differ from the general population. A radical nephrectomy may accelerate the risk of progressive CKD. Genetic testing was not performed. CONCLUSION:Cysts in the kidney, particularly the medulla, should be further examined as a potentially useful imaging biomarker of progressive CKD beyond the current clinical evaluation of kidney function and common CKD risk factors.