genitourinary disorders
Obstructive Uropathy
Diagnosis of Obstructive Uropathy
Urinalysis and serum electrolytes, bloodureanitrogen (BUN), and creatinine Bladder catheterization or bedside ultrasonographic estimation of bladder volume after voiding, sometimes followed by cystourethroscopy and voiding cystourethrography for suspected urethral obstruction Imaging for suspected ureteral or more proximal obstruction or for hydronephrosis without apparent obstruction Obstructive uropathy should be considered in patients with any of the following: Diminished or absent urine output Unexplained renal insufficiency Pain that suggests distention in the urinary tract A pattern of oliguria or anuria alternating with polyuria The history may suggest symptoms of Benign Prostatic Hyperplasia (BPH) , prior cancer (eg, Urinalysis and In an asymptomatic patient with long-standing obstructive uropathy, urinalysis may be normal or reveal only a few casts, white blood cells (WBCs), or red blood cells (RBCs). In a patient with Acute Kidney Injury (AKI) who has a normal urinalysis, bilateral obstructive nephropathy should be considered. If serum chemistries indicate renal insufficiency, obstruction is probably bilateral and severe or complete. Other findings in bilateral obstruction with nephropathy may include Hyperkalemia . Hyperkalemia may result from If urine output is diminished or if there is a distended bladder or suprapubic pain, Bladder Catheterization should be done. If catheterization results in a normal flow of urine or if the catheter is difficult to pass, a urethral obstruction (eg, prostatic enlargement, urethral valve, or Cystourethrography None If symptoms of urethral obstruction are absent or if cystourethroscopy and voiding cystourethrography show no obstruction, the site of obstruction is presumed to be at the ureters or proximal to them. Patients undergo imaging tests to detect the presence and site of obstruction. The choice and sequencing of tests depend on the clinical scenario. Abdominal ultrasonographyis the initial imaging test of choice in most patients without urethral abnormalities because it avoids potential allergic and toxic complications of contrast agents and allows assessment of associated renal parenchymal atrophy. Ultrasonography is aimed at detection of hydronephrosis. However, the false-positive rate is 25% if only minimal criteria (visualization of the collecting systems) are considered in the diagnosis. Also, absence of hydronephrosis (and false-negative results) can occur if obstruction is early (in the first few days) or mild or if retroperitoneal fibrosis or tumor encases the collecting system, preventing dilation of the ureter. Computed Tomography None Ultrasonography None IV urography (IVU) None Antegrade or retrograde pyelographyis preferred to studies that involve vascular administration of contrast agents in patients with azotemia. Retrograde studies are done through a cystoscope, whereas antegrade studies require placement of a catheter into the renal pelvis percutaneously. Patients with intermittent obstruction should be studied when they are having symptoms; otherwise, the obstruction may be missed. Radionuclide Scanning None Magnetic Resonance Imaging None Testing may be necessary to determine whether back or flank pain is caused by obstruction in patients who have hydronephrosis but no obvious obstruction revealed by other imaging tests. Testing may also be done to detect otherwise unrecognized obstruction in patients with incidentally recognized hydronephrosis. Indiuretic renography,a loop diuretic (eg,furosemide0.5 mg/kg IV) is given before a radionuclide renal scan. The patient must have sufficient renal function to respond to the diuretic. If obstruction is present, the rate of washout of the radionuclide (or contrast agent) from the time the tracer appears in the renal pelvis is reduced to a half-life of>20 minutes (normal is<15 minutes). On rare occasions, if the renogram is negative or equivocal but the patient is symptomatic, a perfusion pressure flow study is done via percutaneous insertion of a catheter into the dilated renal pelvis, followed by fluid perfusion into the pelvis at 10 mL/min. The patient is in a prone position. If obstructive uropathy is present, in spite of the marked increase in urine flow, the rate of washout of the radionuclide during renal scanning is delayed, and there will be further dilation of the collecting system and elevation of the renal pelvic pressure to>22 mm Hg during perfusion. A renogram or perfusion study that causes pain similar to the patient’s initial complaint is interpreted as positive. If the perfusion study is negative, the pain probably has a nonrenal cause. False-positive and false-negative results are common for both tests. 