Percutaneous endopyelotomy for the treatment of ureteropelvic junction obstruction

Ureteropelvic junction (UPJ) obstruction occurs where the ureter joins the kidney. It may be attributable to extrinsic factors, but more often the cause is faulty development. Because the helical arrangement of muscle fibers needed for urine transport develops progressively, arrest of this process results in only circularly oriented fibers at the UPJ, an arrangement more likely to be obstructive than conductive.(1) Elongation of the ureter, leaving predominantly longitudinal fibers, would likewise be a poorly conducting arrangement.(2) Other developmental errors, such as agenesis or reduction in fiber numbers, also leads to a nonconducting segment.(3) Extrinsic causes of UPJ obstruction are usually an aberrant vessel or a band passing anterior to the junction, although this structure may contribute to intrinsic causes of UPJ obstruction.