Practice Essentials
Urinary tract obstruction is a blockage of the flow of urine out of the body. It is a common cause of acute and chronic renal failure and may result from a wide variety of pathologic processes, intrinsic and extrinsic to the urinary system. Symptoms and signs of obstruction are often mild, occurring over long periods of time and requiring a high index of suspicion for diagnosis. Early recognition and treatment are the keys to preventing renal loss. Because the degree and duration of obstruction are the chief determinants of renal dysfunction, early recognition and treatment are the keys to preventing renal loss. Urinary tract obstruction should be viewed as a potentially curable form of kidney disease.
The 3 points of narrowing along the ureter include the ureteropelvic junction (UPJ), the crossing of the ureter over the area of the pelvic brim at the level of the iliac vessels, and the ureterovesical junction (UVJ).
Signs of dehydration and intravascular volume depletion can be seen as a result of urinary concentrating defects associated with partial obstruction. Peripheral edema, hypertension, and signs of congestive heart failure from fluid overload may be observed in obstruction from renal failure.
Palpable kidney or bladder provides direct evidence of a dilated urinary collection system.
Rectal and/or pelvic examination is essential in determining whether enlargement of pelvic organs (eg, prostate, uterus) is a possible source of urinary obstruction.
Examination of the external urethra may disclose phimosis or meatal stenosis.
Signs and symptoms
Most acute obstructive uropathies are associated with significant pain or abrupt diminution of urine flow; however, chronic urinary tract obstruction is insidious and requires a careful history and a high index of suspicion. The following may be noted:
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Pain (most common symptom in acute obstruction but typically absent with slowly obstructing conditions)
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Altered patterns of micturition
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Acute and chronic renal failure
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Gross or microscopic hematuria
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Recurrent urinary tract infection (UTI)
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New-onset or poorly controlled hypertension secondary to obstruction and increased renin-angiotensin
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Polycythemia secondary to increased erythropoietin production in the hydronephrotic kidney
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History of recent gynecologic or abdominal surgery
Diagnosis
Physical exam
The physical examination should include the following:
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Evaluation for signs of dehydration and intravascular volume depletion; peripheral edema, hypertension, and signs of congestive heart failure from fluid overload may be observed in obstruction from renal failure
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Palpable kidney or bladder (indicative of a dilated urinary collection system)
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Rectal or pelvic examination to help determine whether enlargement of pelvic organs is a possible source of urinary obstruction.
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Examination of the external urethra for phimosis or meatal stenosis
Lab studies
Laboratory studies that may be helpful include the following:
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Urinalysis and examination of sediment
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Urinary diagnostic indices (eg, sodium, creatinine, osmolality)
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Serum electrolytes (sodium, potassium, chloride, bicarbonate), as well as blood urea nitrogen (BUN), creatinine, calcium, phosphate, magnesium, uric acid, and albumin
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Complete blood count (CBC)
Imaging studies
The goals of any imaging study are to distinguish anatomic etiologies from functional forms of collecting system dilation and to identify the site of blockage. [1, 2, 3, 4] Imaging studies that may be considered include the following:
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CT – Helical CT (especially without contrast) rapidly is replacing kidneys-ureters-bladder (KUB) x-rays as the first step in the radiologic evaluation of the urinary system
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MRI - Where available, MRI quickly is becoming the imaging study of choice for urinary obstruction
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IV pyelography (IVP) – IVP is the procedure of choice for defining the extent and anatomy of obstruction
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Invasive pyelography – This modality provides the same information as IVP without depending on renal function and can be used when the risks of IVP are considered too great
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Ultrasonography – This is the procedure of choice for determining the presence of hydronephrosis
Management
The overriding therapeutic goal is reestablishment of urinary flow. Before specific therapy for obstruction is initiated, the life-threatening complications of obstructive uropathy must be investigated and treatment started.
Once urinary tract obstruction is under consideration, a transurethral bladder catheter should be placed:
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If the catheter is properly placed and fluid returns freely, the catheter tip is probably in the bladder, and obstruction above the bladder should be investigated; if a question still remains, imaging studies may be used to establish proper placement
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If a large PVR volume is noted, obstruction below the bladder should be investigated; catheter drainage should be maintained until the etiology of the obstruction is treated appropriately
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Urine should be drained completely and rapidly from an obstructed bladder; prolonged urine stasis only predisposes the patient to UTI, urosepsis, and renal failure
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A urologist should be consulted when a transurethral catheter cannot provide adequate bladder drainage
Calculi are the most common causes of unilateral obstruction. The following considerations apply:
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Most small renal calculi pass spontaneously; conservative treatment typically suffices
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Surgical drainage is necessary only for patients with unrelenting pain, UTI, or persistent obstruction
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The position of the stone in the ureter determines the preferred method of removal
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Calculi in the renal pelvis and proximal ureter are amenable to nephroscopy and removal under direct visualization
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Percutaneous nephrostomy drainage is used for midureteral stones
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Distal ureter stones can be removed cystoscopically by the use of a loop or basket
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Extracorporeal shock wave lithotripsy is another viable option for stones in any position in the ureter
Bilateral obstruction of the ureters is almost always asymmetric. The following considerations apply:
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For midureteral or proximal ureteral obstruction, percutaneous nephrostomy tube placement is indicated
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For distal obstruction, cystoscopic placement of a ureteral stent can be attempted
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In case of suspected urosepsis from bilateral ureteral obstruction, bilateral percutaneous nephrostomy tubes must be placed
For obstruction of prostatic origin, medical therapy for benign prostate hypertrophy (BPH) has provided a very successful alternative to surgical therapy but should not be offered to individuals presenting with absolute indications for surgical intervention (eg, recurrent urinary retention, recurrent UTIs, renal insufficiency, bladder calculi, recurrent gross hematuria). [5]
Pathophysiology
Normal urine production in an adult is about 1.5-2 L/day. Urine flow depends on 3 factors—a pressure gradient from the glomerulus to the Bowman capsule, peristalsis of the renal pelvis and ureters, and the effects of gravity (ie, hydrostatic pressure).
Obstruction of the urinary tract at any level eventually results in elevation of intraluminal ureteral pressure. With prolonged obstruction, ureteral peristalsis is overcome and increased hydrostatic pressures are transmitted directly to the nephron tubules.
As pressures in the proximal tubule and Bowman space increase, glomerular filtration rate (GFR) falls. After 12-24 hours of complete obstruction, intratubular pressure decreases to preobstruction levels. If complete obstruction is not relieved, a depressed GFR is maintained by decreases in renal blood flow mediated by thromboxane A2 and angiotensin II (AII). With continued obstruction, renal blood flow progressively falls, resulting in ischemia and incremental nephron loss. Thus, obstructive uropathy may lead to obstructive nephropathy. Several phases of obstructive nephropathy may be seen, including an early hyperemia and a late vasoconstriction followed by regulation of GFR post obstruction. Recovery of GFR depends on the duration and level of obstruction, preobstruction blood flow, and coexisting medical illness or infection.
Mortality/Morbidity
Urinary tract obstruction may lead to acute or chronic renal insufficiency or overt kidney failure. Obstruction may lead to a salt-losing nephropathy and urinary concentrating defects. Renal tubular acidosis (RTA) type IV, hyperkalemia, hypomagnesia, and hypophosphatemia are common sequelae of chronic obstruction. Although acute or chronic obstruction may cause urinary tract infection (UTI), other sequelae such as renal calculi, hypertension, and polycythemia are associated with a chronic setting. Ascites is a common sequela of neonatal obstruction syndrome. In cases of acute obstruction, a postobstructive diuresis following relief of the problem is well described.
In adults, incidence and etiology of urinary tract obstruction vary significantly with the age and sex of the patient. In young and middle-aged men, renal calculi are the most common cause of at least temporary obstruction. Rare cases of obstructive uropathy due to seminal vesicle cyst and appendiceal mucocele have been reported. In young and middle-aged women, gynecologic surgery, pregnancy, and cancers of pelvic organs are important etiologies of obstruction.
Special considerations in pediatric patients include acquired or congential urethral stricture, congenital ureteropelvic junction (UPJ) or ureterovesical junction (UVJ) obstruction, vesicoureteral reflux, and urolithiasis.
After age 60 years, urinary tract obstruction is most common in men secondary to prostatic hypertrophy; prostate cancer accounts for occasional cases.
