Pyeloplasty is the surgical reconstruction of the renal pelvis (a part of the kidney) to drain and decompress the kidney. In nearly all cases, the goal of the surgery is to relieve a uretero-pelvic junction (UPJ) obstruction.
Your child has a blockage where the renal pelvis connects with the ureter, the tube that carries urine from the kidneys to the bladder. This narrowing causes dilation of the kidney, a condition called hydronephrosis. Hydronephrosis can usually be verified with an ultrasound and kidney scan.