Illustration of a kidney with a UPJ obstruction, causing dilation of the renal pelvis and calices. In this case, the obstruction is caused by intrinsic narrowing, which is the most common cause of UPJ obstruction.
UPJ: ureteropelvic junction.
Modified from: Baskin LS, Kogan BA. Handbook of Pediatric Urology, 2nd ed, Lippincott Williams & Wilkins 2005.
