Editing Pathophysiology of Urinary Tract Obstruction (section)

==== Ultrasound ====

* '''Hydronephrosis'''
** '''The term hydronephrosis implies dilatation of the renal pelvis and calyces and can occur without obstruction.'''
*** '''Significant hydronephrosis can be present in the absence of obstruction (e.g., vesicoureteral reflux)'''
** '''The term obstructive nephropathy should be reserved for the damage to the renal parenchyma that results from an obstruction to the flow of urine anywhere along the urinary tract.'''
*** '''Significant obstruction can be present in the absence of severe hydronephrosis (e.g., very early in the course of acute renal obstruction)'''
**** Standard renal US may appear normal in 50% of patients with acute urinary obstruction
* '''Resistive index (RI)'''
** '''Definition of RI: (peak systolic velocity–end diastolic velocity)/peak systolic velocity'''
** Changes in intrarenal arterial waveforms have been shown to be associated with urinary obstruction
** '''RI >0.70 has been suggested as a technique to improve detection of urinary obstruction during US.'''
*** However, studies investigating RI in the detection of renal obstruction have not found it useful.
* '''Ureteric jets'''
** '''Color Doppler US can reliably identify ureteric jet dynamics in the bladder'''
** Requires good hydration of the patient
** Limited by the requirement of a normal contralateral collecting system for comparison.