Almost any type of obstructive uropathy can lead to hydronephrosis. The most common causes are benign prostatic hyperplasia, urethral strictures, and calculi. Less common causes include strictures or stenosis of the ureter or bladder neck, congenital abnormalities, and abdominal tumors.

If the obstruction is in the urethra or bladder, hydronephrosis is usually bilateral; if the obstruction is in a ureter, hydronephrosis is usually unilateral. Obstructions distal to the bladder cause the bladder to dilate and act as a buffer zone, delaying hydronephrosis. Total and prolonged obstruction of urine flow with dilation of the collecting system ultimately causes complete cortical atrophy and cessation of glomerular filtration.

The most common complication of an obstructed kidney is life–threatening infection (pyelonephritis) caused by urinary stasis that exacerbates renal damage. If hydronephrosis results from acute obstructive uropathy, the patient may develop paralytic ileus. Untreated bilateral hydronephrosis can lead to renal failure, a life–threatening condition.

The patient’s history and reason for seeking care will vary, depending on the cause of the obstruction. For example, a patient may have no symptoms or complain of only mild pain and slightly decreased urine flow. Or he may report severe, colicky renal pain or dull flank pain that radiates to the groin and gross urinary abnormalities, such as hematuria, pyuria, dysuria, alternating oliguria and polyuria, and anuria.

A patient with hydronephrosis may also report nausea, vomiting, abdominal fullness, pain on urination, dribbling, and urinary hesitancy. Pain on only one side, usually in the flank area, may signal a unilateral obstruction.