ABSTRACT
The etiology of ureteropelvic junction obstruction may result from a number of factors, and can be classified as congenital or acquired in origin. Congenital ureteropelvic junction obstruction is typically characterized by an intrinsic luminal narrowing that is caused by an aperistaltic segment, in which the spiral musculature has been replaced by abnormal longitudinal muscle fibers and fibrous tissue (1-2). A less frequent cause of congenital ureteropelvic junction obstruction is a proximal ureteral stricture caused by abnormal ureteral muscle fiber and collagen deposition in this area (3). Additionally, intrinsic obstruction can be caused by infoldings of ureteral mucosa, a phenomenon that may result from exaggeration of congenital folds that are normally found in the ureter during fetal development (4). In some instances, ureteral adventitia may be present as external bands or adhesions that cause obstruction by producing angulation of the proximal ureter at the lower margin of the renal pelvis. High insertion of the ureter has also been reported as a primary obstructing lesion, and may coincide with other renal anomalies such as ectopia or abnormal fusion (5).
