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

Abstract

The kidney is a lobulated organ, but little is known regarding the clinical importance of the number and size of individual kidney lobes. 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. 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. 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.