• Urinary tract obstruction, not an uncommon problem, can occur at any age.
  
• It can be acute or chronic, partial or complete, with unilateral or bilateral renal involvement.
  
• The diagnosis of obstructive uropathy usually requires the presence of hydronephrosis (dilation of the renal pelvis and calyces), hydroureter, and/or bladder distention.

Patients presenting with unexplained acute or chronic kidney disease, with or without obstructive symptoms, should be evaluated for the possibility of obstructive uropathy. Chronic obstruction can result in chronic tubulointerstitial disease. Bladder outlet obstruction is common in older males due to prostatic hypertrophy or carcinoma. Urinary retention can be seen in both genders postoperatively and as a complication of urinary tract infection.

Patients complaining of voiding dysfunction including hesitancy, decreased force of stream, interruption in stream, or postvoid dribbling should be evaluated for the presence of urinary retention. These symptoms are usually due to prostate disease, urethral stricture, or neurogenic bladder. Medications can often be used to treat many of these symptoms and prevent complications. Patients with bladder spasticity can benefit from anticholinergic agents such as oxybutinin and propantheline bromide. Patients with bladder outlet problems can be treated with α-antagonists, which act by relaxing the smooth muscle of the bladder neck and prostate. Patients with severe bladder atony may require intermittent bladder catheterization.

Symptoms and Signs

Patients with obstruction of a solitary kidney or bilateral obstruction present with acute oligoanuric renal failure. Incomplete obstruction can result in fluctuating urine output. Pain is related to the location, duration, and severity of obstruction. Acute obstruction can result in severe pain due to distention of the collecting system or renal capsule. Renal colic due to calculi is often sudden and severe, with pain beginning in the flank and radiating into the ipsilateral groin. This can be accompanied by nausea and vomiting. Patients with renal colic prefer to be in motion, compared to patients with peritonitis, whose pain is worsened with movement.

A distended bladder on physical examination or the presence of a flank mass is suggestive of obstruction. Hypertension can be seen in obstructive uropathy due to volume expansion and activation of the renin–angiotensin–aldosterone system.

Laboratory Findings

Table 16–1 lists the common laboratory abnormalities in obstructive uropathy. The kidneys lose their ability to concentrate the urine early in obstruction. Later, they cannot concentrate or dilute urine well (isosthenuria). Defects in distal urinary acidification result in a hyperchloremic metabolic acidosis (distal renal tubular acidosis). This can be accompanied by hyperkalemia. Patients will have renal insufficiency if there is bilateral obstruction or obstruction to a solitary functioning kidney. Often the ratio of blood urea nitrogen to serum creatinine will be greater than 10:1 due to increased urea reabsorption throughout the collecting system. Patients with a partial obstruction can have nephrogenic diabetes insipidus (resistance to antidiuretic hormone) and develop hypernatremia. Patients may have polycythemia due to excess erythropoietin production, or may be anemic with more advanced renal impairment. Urinary stasis can result in urinary tract infection with urea splitting bacteria like Proteus and Staphylococcus. This results in an alkaline urine pH and is associated with struvite (magnesium, ammonium, phosphate) calculi.

Imaging Studies