Urinary Tract Obstruction

Published on 26/03/2015 by admin

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116 Urinary Tract Obstruction

A patent urinary tract is necessary for optimal kidney function. Under normal circumstances, urine passes unimpeded from the renal pelvises to the tip of the urethra. Obstruction can occur anywhere along this pathway and may lead to both acute and progressive kidney parenchymal damage.

Several definitions may be encountered when considering urinary tract obstruction:

image Epidemiology

Urinary tract obstruction is a common disorder. On autopsy, 3.1% of adults have hydronephrosis.1 Data from the Healthcare Cost and Utilization Project’s National Inpatient Sample (based on ICD-9 codes) indicate that 1.75% of all hospital discharges are complicated by either hydronephrosis or obstruction.2 When hydronephrosis is excluded, urinary tract obstruction occurs in approximately 1% of hospital discharges.2 Urinary tract obstruction accounts for approximately 10% of community-acquired acute kidney failure35 and is a factor in 2.6% of acute kidney failure cases in the intensive care setting.6

image Etiology

Many disorders may lead to urinary tract obstruction. A useful classification is to first divide causes by the level of obstruction: upper (from the renal pelvis to the ureterovesicular junction) or lower (from the bladder to the urethra) urinary tract. This approach may then be refined into intrinsic versus extrinsic causes.

Upper Urinary Tract Obstruction

Intrinsic Causes

Intrinsic urinary tract obstruction may be due to pathology within the lumen (intraluminal) or within the walls of the collecting system (intramural).

Intraluminal Causes

Obstruction at the level of the renal tubules may be due to crystal-induced disease, uric acid nephropathy (as in the tumor lysis syndrome), or cast nephropathy due to multiple myeloma. Crystal-induced nephropathy has been classically described with sulfadiazine, acyclovir, indinavir, triamterene, and methotrexate.9 Newer literature also implicates orlistat10 and ciprofloxacin.11

Nephrolithiasis is a common cause of upper urinary tract obstruction at the level of the ureter, with the size of the stone determining the likelihood of obstruction. Stones ≤2 mm, 3 mm, 4 to 6 mm and larger than 6 mm will pass spontaneously 97%, 86%, 50%, and 1% of the time, respectively.12 Typically the obstruction occurs at one of the three narrowest portions of the ureter: the UPJ, the ureterovesicular junction (UVJ), or at the point where the ureter crosses over the pelvic brim. The obstruction is usually, but not always, acute and symptomatic. Neoplasms, blood clots, and sloughed renal papillae are rarer causes of intrinsic obstruction at the level of the ureter.

The causes of intraluminal obstruction at the level of the bladder are similar to those affecting the ureter, with urolithiasis, blood clots, and neoplasms being most common. Worldwide, infection with Schistosoma hematobium with resulting fibrosis is a common cause of bladder obstruction.13 Although rare in industrialized nations, it should be suspected in patients from endemic areas such as Africa and the Middle East.

Intramural Causes

Obstruction due to intramural causes is most often seen in the lower urinary tract. Disorders affecting the neuromuscular control of bladder emptying, such as cerebrovascular accidents,14 spinal cord injury,15 multiple sclerosis,16 and diabetic neuropathy17 may lead to bladder outlet obstruction. Multiple medications, including anticholinergics, opioid analgesics, nonsteroidal antiinflammatory agents, α-adrenoreceptor antagonists, benzodiazepines, and calcium channel blockers have also been associated with urinary retention.18 Stricture of the urethra may also lead to obstruction.

One potential intramural cause affecting the upper tract is ureteral stricture due to genitourinary tuberculosis.

Extrinsic Compression

Pregnancy is typically associated with right-sided dilation of the renal pelvis, calyx, and ureter. Hormonal mechanisms and mechanical compression from an enlarging uterus and an enlarging ovarian vein plexus have been implicated in these changes.19 Clinically meaningful obstruction from the gravid uterus is extremely rare.

Malignancies may cause obstruction by several different mechanisms. Local ureteric compression may be seen in metastatic cancers of the cervix, bladder and prostate, as well as with expanding retroperitoneal soft-tissue masses. Alternatively, the ureters may be compressed or encased by metastatic retroperitoneal lymphadenopathy from a distant primary.20

Retroperitoneal fibrosis may lead to obstruction of one or both ureters via inflammation. It is an uncommon disorder, with a reported incidence rate of 1.3 case per million population and a male/female ratio of 3.3 : 1.21 Although the majority of these cases are idiopathic (>75%),22 numerous conditions are suspected to cause retroperitoneal fibrosis, including malignancies, medications, infection, trauma, or radiation.23 Treatment of idiopathic retroperitoneal fibrosis is initially with steroids, but recurrences are common. Case reports describe the use of cyclophosphamide, azathioprine, colchicine, mycophenolate, or tamoxifen for treatment relapses or steroid-resistant disease, although conclusive data are absent.22 Abdominal aortic aneurysms (AAA) may also cause obstruction due to compression of the ureter or via inflammation. A recent series evaluated 999 cases of inflammatory AAA and found preoperative hydronephrosis in 7.4%.24

Extrinsic compression of the lower urinary tract is more common in males. The etiology is usually either benign prostatic hypertrophy or prostate cancer.

The clinician must always bear in mind that hydroureter and/or hydronephrosis may be absent in obstruction due to retroperitoneal processes. Thus, one must maintain a high degree of suspicion and use alternative imaging modalities when considering these disorders.

The etiology of urinary tract obstruction is summarized in Box 116-1.

image Clinical Presentation

The clinical presentation of urinary tract obstruction depends on the location, duration, and severity of obstruction and may therefore be quite variable.