The pathophysiology of UPJ obstruction. Current concepts.

It took more than half of a century for urologists to recognize that hydronephrosis is not necessarily equivalent to obstruction. Keeping this important truism in mind, particularly when dealing with antenatal hydronephrosis, one must also remember that hydronephrosis is not a normal condition. It is conceivable that although the initial intrinsic stenosis or ureterovascular obstruction may not be clinically significant in terms of renal functional damage, as compensatory renal pelvic dilatation develops, secondary obstructive elements may be recruited to create an insertional anomaly and peripelvic fibrosis. The individual types of UPJ obstruction that are seen in diagnostic studies or on the operating table may represent isolated "snapshots" of evolving pathophysiologic processes. If this is true, patients with asymptomatic congenital hydronephrosis, although lacking obvious renal function loss, require long-term follow-up.