Based on information you provided, I would presume he has had issues related to obstruction for some time hence the Mitrofanoff. The radiologic reports are suggesting the following: 1. The kidney sizes mentioned are within normal range, perhaps the Left a bit smaller. In general I would conside between 9 and 12 cm normal sized. The discrepency in the size of his kidneys is within physiologic normal range and that in and of itself would not be concerning 2. The cortex of the kidney is where majority the functional units of the kidney are located ie the microscopic parts that are responsible for filtration and urine formation. Cortical thinning would indicate some loss of these functional units perhaps from prior injury or scarring. I would be considered a marked of what is termed Chronic Kidney disease. The ultrasound itself would not be the determinant of his kidney function. This would be assesed based on blood tests and certain urine assessments 3. The calyx is a portion within the collecting system. In your sons condition, I would presume there was/or is some degree of reflux (urine refluxing back into the ureter). This is likely the cause of the calyceal dilation. Stone, stricture, scarring, mass are other causes but based on your recent Ultrasound not commenting on such a finding and his history, this seems less likely