Association of Kidney Cysts With Progressive CKD After Radical Nephrectomy

Abstract

Rationale & objective: Simple kidney cysts, which are common and usually considered of limited clinical relevance, are associated with older age and lower glomerular filtration rate (GFR), but little has been known of their association with progressive chronic kidney disease (CKD).

Study design: Observational cohort study.

Setting & participants: Patients with presurgical computed tomography or magnetic resonance imaging who underwent a radical nephrectomy for a tumor; we reviewed the retained kidney images to characterize parenchymal cysts at least 5mm in diameter according to size and location.

Exposure: Parenchymal cysts at least 5mm in diameter in the retained kidney. Cyst characteristics were correlated with microstructural findings on kidney histology.

Outcome: Progressive CKD defined by dialysis, kidney transplantation, a sustained≥40% decline in eGFR for at least 3 months, or an eGFR<10mL/min/1.73m² that was at least 5mL/min/1.73m² below the postnephrectomy 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. Nonparametric 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 1,195 patients with 50 progressive CKD events over a median 4.4 years of follow-up evaluation. On baseline imaging, 38% had at least 1 cyst, 34% had at least 1 cortical cyst, and 8.7% had at least 1 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 of medullary cysts was more strongly associated with progressive CKD than the number 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.

Conclusions: 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.

Plain-language summary: Kidney cysts are common and often are considered of limited clinical relevance despite being associated with lower glomerular filtration rate. We studied a large cohort of patients who had a kidney removed due to a tumor to determine whether cysts in the retained kidney were associated with kidney health in the future. We found that more cysts in the kidney and, in particular, cysts in the deepest tissue of the kidney (the medulla) were associated with progressive kidney disease, including kidney failure where dialysis or a kidney transplantation is needed. Patients with cysts in the kidney medulla may benefit from closer monitoring.

Keywords: Chronic kidney disease; kidney failure; medulla; radical nephrectomy; simple kidney cysts.

Figure 1.

Examples of renal cysts in different locations. Contrast-enhanced CT (corticomedullary phase) of the kidney in various reformats show A) an exophytic cortical cyst, B) an endophytic cortical cyst, and C) a cyst in the medulla (indicated by white arrows).

Figure 2.

Selection of study population.

Figure 3.. Risk of progressive CKD with number of cortical and medullary cysts.

Higher number of A) cortical cysts and B) medullary cysts were associated with progressive CKD (Log-rank p=0.004 for both).