The Number and Size of Individual Kidney Medullary Pyramids is Associated with Clinical Characteristics, Kidney Biopsy Findings, and CKD Outcomes among Kidney Donors

Abstract

Background: The kidney is a lobulated organ, but little is known regarding the clinical importance of the number and size of individual kidney lobes. Methods: After applying a previously validated algorithm to segment cortex and medulla, a deep-learning algorithm was developed and validated to segment and count individual medullary pyramids on contrast-enhanced computed tomography (CT) images of living kidney donors prior to donation. The association of cortex volume, medullary volume, number of pyramids, and mean pyramid volume with concurrent clinical characteristics (kidney function and chronic kidney disease risk factors), kidney biopsy morphology (nephron number, glomerular volume, and nephrosclerosis), and short- and long-term glomerular filtration rate (GFR) <60 or <45 ml/min/1.73m2 was assessed. Results: Among 2,876 living kidney donors, 1,132 had short-term follow-up at a median of 3.8 months and 638 had long-term follow-up at a median of 10.0 years. Larger cortical volume was associated with young age, male, larger body size, higher GFR, albuminuria, more nephrons, larger glomeruli, less nephrosclerosis, and lower risk of low GFR at follow-up. Larger pyramids were associated with older age, female, larger body size, higher GFR, more nephrons, larger glomerular volume, more nephrosclerosis, and higher risk of low GFR at follow-up. More pyramids were associated with younger age, male, greater height, no hypertension, higher GFR, lower uric acid, more nephrons, less nephrosclerosis, and a lower risk of low GFR at follow-up. Conclusions: Cortical volume and medullary pyramid volume and count reflect underlying variation in nephron number and nephron size, as well as merging of pyramids due to age-related nephrosclerosis, with loss of detectable cortical columns separating pyramids.

Associations of MRI-derived kidney volume, kidney function, body composition and physical performance in ≈38 000 UK Biobank participants: a population-based observational study

“…The clinical implications of kidney volume in relation to clinicodemographic factors that may be critical for health-related conditions remain largely unclear. Previous studies have shown a linkage between kidney volume and function [ 12 , 21 , 38 , 39 ] and a small kidney has been considered an indicator for increased risk of CKD or decreased renal function, as kidney volume is closely related to the number and size of nephrons, which determine kidney function [ 8 , 40–43 ]. Interestingly, kidney volume has previously been indicated to be associated with age, sex, weight and even muscle mass or intense physical activity [ 9 , 23–26 ].…”

Prognostic Utility of Total Kidney Volume for Chronic Kidney Disease Risk Prediction: An Observational and Mendelian Randomization Study

“…[4][5][6] Larger volumes are presumed to represent greater nephron endowment leading to increased glomerular filtration rate. 7,8 Correspondingly, patients with advanced CKD show significant shrinkage of the kidneys as a result of atrophy. 9 However, the causal directionality between TKV and CKD has not been tested beyond observational studies.…”