Urinary tract obstruction can occur at any point in the urinary tract, from the calyces to the external urethral meatus. Obstruc-tion can be congenital or acquired, and malignant or benign. The obstruction may be partial or complete, and unilateral or bilateral. The baseline renal function is important in determining the impact that any obstruction will have. Obstructive uropathy can result in pain, infection, sepsis and loss of renal function. A logical approach to this would be to divide this topic into upper urinary tract obstruction and lower urinary tract obstruction.
James Hall MBChB FRCS Urol is a Consultant Urological Surgeon at the
Royal Hallamshire Hospital, Sheffield, UK, and is Training Program
Director for Urology in South Yorkshire. He qualified from Sheffield
Medical School in 1990 and then undertook his Urological training
initially in stockport, then at SPR level on the North Trent Rotation. His
main interests are in endourology and urinary stone disease. Conflicts
of interest: none declared.
Kate D Linton MBChB MRCS(Ed) is a Specialist Registrar in Urology on the
North Trent Training Rotation, UK. Conflicts of interest: none declared.
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Upper urinary tract obstruction
Acute obstructionThis is most frequently due to a ureteric stone. Acute ureteric colic (usually associated with acute obstruction) is extremely painful, often the worst pain a patient has ever experienced. The pain is usually in the loin, radiating to the groin and even to the genitals. Ureterovesical junction stones can also present with voiding symptoms and strangury. Analgesics are an urgent requirement for these patients before imaging can be considered. Non-contrast CT kidney–ureter–bladder scanning (NCCT-KUB) is now the preferred diagnostic test as almost all stones (99%) are visible on CT. Indinivir stones caused by the antiretroviral drug are radiolucent on CT; however, a thorough history should give a clue to these stones. If loin pain is not due to a stone then NCCT-KUB may elucidate an alternative diagnosis for the cause of the pain. Some causes of acute obstruction are listed in Table 1.
Chronic obstructionThere are many chronic causes of upper tract obstruction (Table 2). The most common in the Western world are calculi and pelvi-ureteric junction (PUJ) obstruction. Chronic obstruc-tion may result in deterioration of renal function and eventual renal failure, which in some patients can be silent. Chronic obstruction can also lead to sepsis, which may require emer-gency decompression. When pain is experienced in chronic upper tract obstruction it has the same radiation as acute obstruction, although is usually less severe and can be mistaken as musculo-skeletal discomfort. Often chronic obstruction is picked up as an incidental finding on imaging performed for another reason or for the investigation of renal impairment.
Investigations in upper urinary tract obstruction
Imaging is the cornerstone of the investigation for upper tract obstruction, but the following tests should be performed or at least considered before imaging.
Physical examination should be performed, including pelvic examination/digital rectal examination to exclude palpable pel-vic malignancy.
Urea and electrolytes will give an indication of the degree of urgency and whether any biochemical abnormality needs correcting, e.g. hyperkalaemia. Full blood count will include a WBC count, which will help in the assessment of whether infec-tion is present. Dipstick of the urine, particularly for blood and
Some causes of acute upper urinary tract obstruction
nitrites, is important and a mid-stream specimen of urine should be sent for microscopy, culture and sensitivity.
Flexible cystoscopy may be needed, particularly in the pres-ence of bilateral obstruction which could be due to bladder base pathology.
Kidney–ureter–bladder X-rayA plain radiograph including kidneys, ureters and bladder (KUB X-ray) is often an initial investigation in undiagnosed loin pain (Figure 1). Only 50–60% of urinary tract calculi are visible on a KUB X-ray. Once a stone has been diagnosed on CT scan a retro-spective review of a KUB X-ray is recommended. If visualized on a KUB X-ray the stone can be followed up with sequential X-rays rather than further CT scans, which give a much larger dose of radiation. There can be useful clues to alternative diagnoses on the X-ray, such as a calcified aortic aneurysm, a full bladder or bowel gas patterns, which may indicate other pathology.
UltrasonographyThis is a cheap, easy non-invasive investigation that can be per-formed in the presence of allergies to contrast, pregnancy and renal failure. Dilatation of the upper tracts can be evidenced by
Some causes of chronic upper urinary tract obstruction
Renal
• Congenital obstruction at the PuJ
• aberrant vessel at the PuJ
• Renal cell carcinoma
• Transitional cell carcinoma in the renal pelvis
• Tuberculosis
• Calculi
Ureteric
• Stricture
• ureterocele
• ureteric valves
• Retrocaval ureter
• Tuberculosis
• Calculi
• Transitional cell carcinoma in the ureter
• ureteritis cystica
• aortic aneurysm
• Radiation
• Retroperitoneal fibrosis
• Pregnancy
• Para-aortic lymph nodes
• Iatrogenic
• Intra-abdominal malignancy
Bladder
• Transitional cell carcinoma
• neurogenic bladder
• Pelvic malignancy
PuJ, pelvi-ureteric junction.
Table 2
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hydronephrosis (Figure 2) and hydro-ureter, although dilatation does not necessarily indicate obstruction. Stones can be seen by their acoustic shadows as well as other intra-abdominal patho-logy. In the presence of a full bladder the use of Doppler imag-ing can show the ureteric jets, which can be helpful in deciding whether obstruction is complete or not. There is interobserver variability, and obesity and large amounts of bowel gas may give suboptimal views. Parapelvic cysts may mimic hydronephrosis and vice versa. In the acute setting, obstruction sometimes does not lead to dilatation of the pelvicalyceal system and so may not be apparent on ultrasound. If ultrasound is normal, but the patient has unexplained loin pain with or without sepsis, other imaging
should be considered, such as a stone protocol non-contrast CT or an intravenous urogram (IVU).
CT (Figures 3 and 4)NCCT-KUB scans are now the preferred imaging modality in acute loin pain. Ureteric and pelvicalyceal dilatation, perirenal and peri-ureteric oedema (seen as stranding), and thickening of the ureteric wall are all signs of acute obstruction. The presence of these signs but no visualization of a calculus may indicate recent passage of a stone. Other pathology can be shown with the scan, such as acute appendicitis, diverticular disease and abdominal aortic aneurysm. NCCT-KUB is fast, sensitive and easily interpreted; it avoids the use of contrast, and is safe in patients with allergies, in renal fail-ure and in diabetics. NCCT-KUB is the investigation of choice in patients with obstructive renal failure, as a level of obstruction and some information about the cause can often be found.
The administration of intravenous contrast increases the diag-nostic yield from CT scanning. Typically, multiphase CT is per-formed, starting with a non-contrast scan. An arterial phase is obtained approximately 20 seconds after administration of intra-venous contrast, then a portal venous phase, which will show the kidneys and liver approximately 70 seconds after injection. Delayed scans of the kidneys can be performed at 2 minutes for optimal parenchymal definition or a few minutes later for col-lecting system visualization. Clearly it is important to have direct dialogue with the radiology department to help get optimal infor-mation from a CT scan so that the scanning protocol can be tai-lored to the clinical question being asked.
Intravenous urogram (Figure 5)This involves intravenous contrast administration after capture of a control image and then serial radiographs of the urinary tract. An IVU can give information on both structure and function of the uri-nary tract. Delayed excretion by the obstructed kidney and a dense
Figure 3 non-contrast CT kidney–ureter–bladder scan in the coronal
plane showing a stone (arrow) in the left ureter with hydronephrosis.
Perinephric stranding can be seen (perirenal oedema).
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nephrogram are the main signs of acute obstruction. Dilatation of the upper tract to the point of obstruction gives information about the level of the obstruction and the cause. A retrospective review of the control film may show a stone not previously appreciated. Allergy to contrast media, nephrotoxic effects of contrast, especially in diabetic, septic and dehydrated patients, and poor excretion of the contrast in renal impairment are the main disadvantages of this imaging modality. In obstruction, delayed films may be required which it may be necessary to perform up to 24 hours later.
Figure 4 CT scan showing left hydronephrosis (arrow) due to a
transitional cell carcinoma in the left ureter.
Figure 5 Intravenous urogram showing bilateral hydronephrosis due to
Retrograde pyelographyRetrograde injection of contrast through a ureteric catheter via a cystoscope can yield information about intraluminal causes of obstruction. Although this can be performed via a flexible cys-toscope under local anaesthetic it is often carried out via a rigid cystoscope under general or regional anaesthesia. This may be performed where other tests have failed to delineate the anat-omy sufficiently. It can be used in patients with renal failure or at risk from intravenous iodinated contrast media. Given the increasingly widespread availability of semirigid and flexible ure-teroscopes, retrograde studies are often only performed under anaesthetic as a prelude to ureteroscopy.
MRIThis method of imaging can accurately show the presence of hydronephrosis, but has poor sensitivity for stone disease. The concomitant administration of a diuretic can help with this. MRI can be used in pregnancy and in patients with renal failure or in whom iodinated contrast media cannot be used. For these rea-sons it is at times an attractive imaging modality. Cost, availabil-ity and time for acquisition of images are all cited as limitations.
Nuclear medicine imagingNuclear imaging is a useful imaging modality for suspected obstruc-tion. Scans can be either static or dynamic. Static imaging, such as technetium-99 dimercaptosuccinic acid (DMSA) scan, is the most accurate test for the estimation of split function of the kidneys. It can also be used for visualization of cortical lesions, for example scars in children with urinary tract infections (UTIs).
Technetium-99 mercaptoacetyl triglycine (MAG3) and tech-netium-99 diethylenetriamine penta-acetic acid (DTPA) are most commonly used in dynamic scans which evaluate obstruction. Rel-ative function and obstruction is assessed by computer-generated clearance curves. Intravenous administration of a diuretic, such as frusemide 0.5 mg/kg, can improve the diagnostic accuracy in obstruction by provoking diuresis and so putting the kidney ‘under stress’. If no obstruction is demonstrated at maximal diuresis then it is highly unlikely that obstruction is present.
Management of upper urinary tract obstruction
Management of upper tract obstruction depends upon the cause, whether the obstruction is unilateral or bilateral, and the pres-ence or absence of renal impairment and of sepsis.
Acute decompressionThe presence of sepsis and upper tract obstruction is a urologi-cal emergency. A pyonephrosis may be present (Greek pyon – pus, nephros – kidney). In this instance the treatment options are percutaneous nephrostomy or JJ stent insertion. The initial treatment of choice in our centre would be the placement of a percutaneous nephrostomy, which involves placing a 8-F tube into the collecting system using ultrasound and X-ray guidance. Subsequently this can be used for placement of antegrade stents or for access for percutaneous stone surgery if necessary. Before nephrostomy tube insertion the ‘3Cs’ are required: coagulation, intravenous cefuroxime and consent. Nephrostomy tube place-ment is not without risk and so patients should be counselled appropriately. A full blood count and clotting screen should be
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performed well in advance and any abnormalities corrected. Intravenous cefuroxime is administered before the procedure, although many patients will already be receiving antibiotics.
JJ stent insertion requires an anaesthetic, which is less than ideal in patients who are either in renal failure or septic. It requires instrumentation of the urinary tract, which is best avoided in the presence of sepsis. Nephrostomy tubes generally drain better than stents. It will be impossible to place stents retrogradely in some patients, especially those whose obstruction is due to pelvic malig-nancy or bladder base pathology as the ureteric orifices will be extremely difficult to visualize. A trial of nephrostomy tube clamp-ing can be performed before removal, once the cause of obstruction has been treated. Should be patient develop sepsis, pain or dete-riorating renal function, the tube can easily be unclamped on the ward. Other than sepsis, renal failure with fluid overload or hyper-kalaemia are indications for urgent nephrostomy tube placement.
Patients with renal failure due to upper tract obstruction or obstruction from a malignant cause requiring chemotherapy and optimal renal function, also undergo decompression by means of either nephrostomy tube or JJ stent insertion. There are some patients with renal failure, however, in whom initial dialysis is more appropriate.
CalculiObstruction due to calculi often presents acutely with unilateral pain. However, calculi can cause bilateral obstruction and silent chronic obstruction. The treatment for calculi depends on their size and location within the upper tract. Treatment modalities include extracorporeal shock wave lithotripsy, ureteroscopy and stone fragmentation, percutaneous nephrolithotomy and lapa-roscopic stone surgery. Open stone surgery is occasionally per-formed but has been mainly superseded by laparoscopic surgery (see Further Reading).
Pelvi-ureteric junction obstructionCongenital PUJ obstruction results from an aperistaltic segment of the ureter, which consequently results in the failure to generate a proper peristaltic wave for propagation of urine from the renal pelvis down the ureter. The primary goal of intervention in PUJ obstruction is to relieve symptoms and to preserve or improve renal function. There are several surgical modalities. Traditionally an open dismembered pyeloplasty is performed with resection of the adynamic segment of ureter. Laparoscopic pyeloplasty is the favoured surgical option in many centres, with a significant reduc-tion in morbidity and postoperative in-patient stay. Endourological options include endopyelotomy, endoburst and balloon dilatation. These are less effective than open or laparoscopic pyeloplasty, but are useful in patients with significant morbidity who are unsuit-able for either laparoscopic or open pyeloplasty. Long-term stent-ing is another treatment option, but stents will need to be changed every 6 months under some form of anaesthesia.
Unrecognized PUJ obstruction can result in a poorly function-ing or non-functioning kidney. In these circumstances the best option may be nephrectomy to reduce the risk of complications.
Other treatmentsThe management of the many other causes of upper tract obstruc-tion are outside of the remit of this article. See Further Reading if more detail is required.
Lower urinary tract obstruction is obstruction below the level of the ureteric orifices. This encompasses obstruction at the bladder neck, prostate and at any point along the urethra. Some causes are shown in Table 3.
Acute obstructionAcute lower urinary tract obstruction presents with painful retention of urine. Often there are preceding lower urinary tract symptoms or a precipitating cause, but it can present as de novo retention. Patients usually have suprapubic discomfort but can have severe pain mimicking an acute abdomen and are unable to void. The disappearance of their symptoms with the insertion of a catheter is a welcome relief. Once the patient has been cath-eterized a record must be made of the residual volume present within the bladder. Once the bladder has been drained either by urethral catheter or, if necessary, suprapubic catheter, it is neces-sary to establish the cause and formulate a subsequent manage-ment plan. Common precipitating causes of acute retention of urine in men are stress, drugs such as anticholinergics, alcohol, and anaesthetic agents related to surgery.
Acute retention in men over 50 years of age is a common reason for emergency admission in urology. The cause of acute retention in younger men and also in women clearly will not be benign prostatic enlargement (BPE). In younger men the cause may be a urethral stricture, which will be more apparent when a urethral catheter will not pass. Neurological causes are also a possibility. Cord compression should be considered, particularly if the patient has back pain or a malignancy such as prostate can-cer which metastasizes to the spine. A full neurological examina-tion is mandatory along with a rectal examination to assess anal tone and perianal sensation. MRI is mandatory should there be any concern regarding cord compression as the cause of reten-tion of urine. High-dose dexamethasone should be commenced if cord compression is proven and immediate discussions held with the neurosurgeons regarding further management.
In women with acute retention, spinal cord or cauda equina compression needs to be considered as well as the possibility of other neurological diagnoses. A pelvic examination is mandatory as pelvic masses can cause retention as well as mimicking reten-tion. If bladder scanning shows a women to have a full bladder and yet there is little residual urine in the bladder when she is
Some causes of lower urinary tract obstruction
• Benign prostatic enlargement
• urethral stricture
• Meatal stenosis
• Phimosis
• Prostate cancer
• uterine prolapse
• Cystocele
• detrusor sphincter dysynergia
• urethral diverticulum
• Stone or foreign body in the urethra
Table 3
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catheterized, the possibility of a cystic lesion in the pelvic organs (e.g. ovaries) must be considered and a pelvic scan should be performed.
Chronic obstructionChronic lower urinary tract obstruction can lead to changes within the bladder, such as diverticula formation and bladder wall thickening, and eventually can lead to detrusor decompen-sation. Eventually upper tract dilatation and hydronephrosis can occur with subsequent renal impairment. Patients with chronic lower urinary tract obstruction can present with frequency, noc-turia, urgency, nocturnal incontinence, recurrent UTIs, poor stream, hesitancy, incomplete emptying and suprapubic discom-fort. Nocturnal enuresis can be a symptom of chronic retention; it will often need direct questioning for patients to admit to it. Occasionally the first presentation is renal failure, with a large palpable non-tender bladder.
Investigations in lower urinary tract obstruction
Physical examination of the patient will give a good idea about the cause of the obstruction. In men a digital rectal examination and in women a pelvic examination must be performed.
Bladder scanning will give a good estimate of the amount of urine within the bladder after voiding. Any voided urine or cath-eter specimen of urine can be subjected to dipstick testing and microscopy, culture and sensitivity.
Urea and electrolyte measurements must be performed as patients with chronic obstruction may have an element of renal impairment.
Flexible cystoscopyFlexible cystoscopy can be useful, especially if urethral cathe-terization has not been possible, to rule out strictures or other anatomical abnormalities. Flexible cystoscopy is also advisable If frank haematuria has been noted as occasionally a tumour at the base of the bladder can present as retention of urine.
UltrasoundUltrasound of the urinary tract is useful in patients who have renal impairment to assess whether there is hydronephrosis or hydro-ureter. This is particularly useful if the patient’s creatinine level does not start to improve within 24 hours of relief of the obstruction.
Urinary flow ratesPeak urinary flow rates are performed in men to establish whether there is outflow obstruction. The shape of the flow trace can give an indication of the cause of obstruction. A very flat prolonged trace can indicate a urethral stricture. Flow rates are dependent on the volume voided; if the volume voided is too large or too small the detrusor contracts inefficiently and a false reading is obtained. A voided volume of at least 150 ml is required to get a representative trace. It is generally thought that a peak flow rate (PFR) of more than 15 ml/second is most likely to be non-obstructed. A PFR of less than 10 ml/second is most likely to be obstructed and one of 10–15 ml/second is equivocal. A low flow rate can be caused by detrusor failure and so a pressure–flow urodynamic assessment can be important before surgical intervention.
UrodynamicsUrodynamics is used to provide objective functional tests of blad-der and urethral function. It essentially evaluates pressure and flow with or without fluoroscopy, depending on the facilities available. An 8-F biluminal catheter is inserted into the blad-der and a pressure measurement line in the rectum. Detrusor pressure is estimated by subtracting the rectal pressure (as an index of intra-abdominal pressure) from the total bladder pres-sure (intravesical pressure). During the study the bladder is filled at 50 ml/minute with contrast medium or saline, depending on whether there are fluoroscopic facilities. A note is made of the initial bladder residual volume, bladder volume at the time of first sensation to void, the final tolerated volume and the residual volume after voiding. Patients are asked to void into a flowmeter to obtain a PFR. Those with urinary incontinence are asked to cough or to wash their hands to try to reproduce their inconti-nence during the study.
The results of these pressure–flow studies can be classi-fied according to a number of nomograms, the most common being the Abrams–Griffiths nomogram. Patients are classified as obstructed, unobstructed and equivocally obstructed. The Abrams–Griffiths number (AG) can be calculated by subtracting twice the maximum flow rate (Qmax, in ml/second) from the detrusor pressure at maximum flow (PdetQmax, in cm H2O). AG = PdetQmax − 2Qmax. Obstruction is present if the number is more than 40, equivocal if it is 20–40 and unobstructed if it is less than 20 cm H2O.
In men with chronic retention, urodynamics can help in deciding whether a transurethral resection of prostate (TURP) is appropriate; if they are obstructed and generate good detrusor pressures then they are likely to have a good outcome. Video-urodynamics can be helpful in the younger man who appears to have obstruction, as well as in women.
Management of lower urinary tract obstruction
Acute obstructionIn the acute setting catheterization is the initial management of the obstruction. In older men in whom the cause is believed to be BPE, 48 hours of α-blockers followed by a trial without catheter may be appropriate.
In some men in whom there has been an obvious precipitating cause for the retention, such as an anaesthetic, drugs or alco-hol, a period of clean intermittent self-catheterization will allow them to start voiding normally again. Less than a quarter of men who develop postoperative retention will actually have proven obstruction on urodynamics, and to treat all of them as if they had retention due to BPE is not correct clinical management.
In the longer term, men who are troubled by lower urinary tract symptoms or who are catheter dependent can be offered a TURP.
In men under 50 years of age there is usually another cause for the obstruction. In some it may be a tight bladder neck, which can be diagnosed on urodynamics. This may be amenable to a bladder neck incision under anaesthetic. Urethral strictures will require urethrotomy under anaesthetic. However, approximately 50% recur and require further treatment with either further ure-throtomies or reconstructive urethral surgery (urethroplasty).
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Chronic obstructionChronic retention is the painless retention of more than 300 ml of urine. Chronic retention can be divided into high-pressure and low-pressure types, the ‘pressure’ referring to the intra-vesical pressure at the end of micturition. High-pressure chronic retention is associated with bilateral hydronephrosis, whereas low-pressure retention is not. The initial treatment for chronic retention is catheterization. Patients who present acutely owing to chronic retention may have very high residuals within the bladder, sometimes in excess of 2 litres. In patients with high-pressure chronic retention there may be an element of renal fail-ure, known as interactive obstructive uropathy. These patients require catheterization, treatment of hyperkalaemia if present, and close monitoring of their fluid status. Lying and standing blood pressures will give an indication as to whether the patient is losing too much fluid. There may be a profound postobstruc-tive diuresis following relief of the obstruction. Initially patients should be advised to drink according to their thirst, with close monitoring of their input and output. Intravenous fluids should be avoided initially as this will drive the diuresis. If the diuresis has not settled after 12 hours (i.e. the patient has a urine out-put of more than 200 ml/hour for 12 hours) then intravenous fluids should be considered. The patient can be discharged with a catheter once renal function has stabilized, and plans have been made to deal with the cause of the obstruction if possible. Patients with chronic low-pressure retention do not have associ-ated renal impairment due to their bladder dysfunction.
Men with BPE and lower urinary tact symptoms can be treated with α-blockers and 5-α-reductase inhibitors, if appropriate. Those men who have consistently high post-void residual urine scans can be taught clean intermittent self-catheterization. This will help to lessen the risk of UTI and may reduce their symp-toms. Some of these men can be offered a TURP, but urodynam-ics is prudent in some to ensure good outcomes from surgery.
Other treatmentsThe management of all of the other causes of lower tract obstruction is outside of the remit. See Further Reading for more information. ◆
FURThER REAdINg
Mundy aR, Fitzpatrick JM, neal de, george nJR, eds. The scientific basis
of urology, 2nd edn. Taylor and Francis, 2004.
Thomas B, Hall J. urolithiasis. Surgery 2005; 23: 129–33.
