Management of urinary tract obstruction

INTRODUCTION — Urinary tract obstruction (UTO) results from a blockage to urine flow along the urinary tract. UTO is typically diagnosed with an imaging study (such as a kidney ultrasound) that reveals hydronephrosis. UTO can be acute or chronic, unilateral or bilateral, and partial or complete. In patients with kidney function impairment as a result of UTO, prompt reversal of the obstruction generally leads to improvement of kidney function. Uncorrected UTO can lead to progressive loss of kidney function.

The management of urinary tract obstruction is discussed in this topic. Related issues are presented elsewhere:

●Hydronephrosis in infants and children (see "Congenital ureteropelvic junction obstruction" and "Primary megaureter in infants and children" and "Clinical presentation and diagnosis of posterior urethral valves" and "Management of posterior urethral valves" and "Fetal hydronephrosis: Etiology and prenatal management" and "Postnatal evaluation and management of hydronephrosis")

●Clinical manifestations and diagnosis of UTO (see "Clinical manifestations and diagnosis of urinary tract obstruction (UTO) and hydronephrosis")

●Findings related to UTO on imaging (see "Radiologic assessment of kidney disease")

●Management of UTO with ureteral stents (see "Placement and management of indwelling ureteral stents")

GENERAL PRINCIPLES — Urinary tract obstruction can be caused by (table 1):

●Lower tract obstruction – Lower tract obstruction is caused by bladder dysfunction or bladder outlet obstruction. These patients present with an elevated postvoid residual and, typically, bilateral hydronephrosis (unilateral hydronephrosis should raise suspicion for upper tract [ie, supravesicular] obstruction). The initial treatment is bladder decompression (ie, placement of a bladder catheter).

Distinguishing between bladder dysfunction and bladder outlet obstruction is accomplished with pressure flow urodynamic testing, which is not performed when patients are acutely ill and require urgent relief of obstruction.

●Upper tract obstruction – Upper tract obstruction is due to problems in the ureters or kidneys. These patients present with either unilateral or bilateral hydronephrosis. In patients with bilateral hydronephrosis, upper tract obstruction should be suspected if the postvoid residual is normal or the hydronephrosis persists despite bladder decompression. Patients who need urgent relief of upper tract obstruction can be treated with placement of a percutaneous nephrostomy tube (PCN), a percutaneous nephroureteral stent (PCNU), or a cystoscopic ureteral stent.

DETERMINING THE URGENCY OF TREATMENT — In some instances, UTO is considered an emergency or urgency and should be relieved as soon as possible [1-4]:

●Emergencies (obstruction should be relieved within several hours):

•Urosepsis (or signs of impending sepsis due to urinary tract infection)

•Severe metabolic abnormalities (eg, hyperkalemia)

●Urgencies (obstruction should be relieved within 24 hours):

•Acute kidney injury (AKI)

•Bilateral UTO or obstruction of a single functioning kidney

In patients with a UTO emergency or urgency, an interventional procedure is performed (options include bladder decompression for lower tract obstruction or percutaneous placement of a nephrostomy tube or nephroureteral stent, or cystoscopic placement of a ureteral stent for upper tract obstruction). In some cases, the cause of obstruction (eg, kidney stone) can be addressed during the same procedure. (See 'When relief of obstruction is urgent' below.)

Among other patients with UTO, those who have one or more of the following should also have the obstruction relieved promptly, although these are not considered emergencies or urgencies:

●Severe chronic kidney disease or kidney impairment of unclear duration

●Severe symptoms attributable to the obstruction (eg, unyielding pain)

In these patients who need prompt management of UTO, an interventional procedure to decompress the urinary tract is typically performed (eg, nephrostomy tube or stent), unless the underlying cause of obstruction can be addressed quickly (eg, kidney stone removal). (See 'When relief of obstruction is urgent' below.)

Unlike in the patients just described, the underlying cause of obstruction can often be addressed first (without the need to first perform nephrostomy tube or stent placement) among those who meet all of the following criteria:

●Unilateral UTO (in a patient with two kidneys)

●Normal kidney function or nonsevere chronic kidney disease

●No concerning electrolyte abnormalities

●No evidence of urinary tract infection

As an example, in patients with a unilateral obstructing kidney stone that is <10 mm in diameter, patients are typically managed with observation, medical expulsive therapy, and pain control while waiting for the stone to pass. (See 'When relief of obstruction is nonurgent' below.)

Assessment of kidney function and the definition of chronic kidney disease are presented elsewhere. (See "Assessment of kidney function" and "Definition and staging of chronic kidney disease in adults".)

WHEN RELIEF OF OBSTRUCTION IS URGENT — UTO due to bladder dysfunction or bladder outlet obstruction can be managed quickly by insertion of a urinary catheter to drain the bladder. (See 'Lower tract (bladder) obstruction' below.)

Urgent relief of upper tract obstruction is accomplished with a percutaneous approach (placement of either a percutaneous nephrostomy tube [PCN] or a percutaneous nephroureteral stent [PCNU]) or a cystoscopic approach (ureteral stent placement). (See 'Upper tract obstruction' below.)

A PCN is a catheter with a locking loop that is placed via a posterior renal calyx to the renal pelvis. A PCNU also enters via a posterior renal calyx and traverses the renal pelvis, but the catheter extends through the ureter to the urinary bladder [5]. PCN and PCNU are typically inserted by interventional radiologists or interventional nephrologists using ultrasound and/or fluoroscopy guidance; generally, these procedures do not require general sedation or general anesthesia. Technical aspects of PCN and PCNU placement are discussed elsewhere. (See "Percutaneous nephrostomy tubes".)

Retrograde ureteral stent placement is performed by a urologist using cystoscopic guidance; frequently, general sedation or general anesthesia is required. Technical aspects of cystoscopic ureteral stent placement are presented separately. (See "Placement and management of indwelling ureteral stents".)

After the obstruction is relieved, the underlying cause of the obstruction should be corrected (table 1). This is presented below. (See 'Treating the underlying cause of UTO' below.)

Lower tract (bladder) obstruction — Patients with bilateral hydronephrosis and evidence of incomplete bladder emptying have a presumed diagnosis of bladder dysfunction or bladder outlet obstruction. Incomplete bladder emptying is documented with a bedside bladder scan showing a postvoid bladder volume of 300 mL or more, or a postvoid bladder catheterization draining 200 mL of urine or more [6].

Such patients require bladder decompression until the underlying cause of obstruction is corrected. (See 'Treating the underlying cause of UTO' below.)

Ongoing bladder decompression may be accomplished by one of the following:

●Clean intermittent catheterization (preferred approach) – Clean intermittent catheterization is continued until the postvoid residual is less than 300 mL (this is the preferred approach). Clean intermittent catheterization should be performed as infrequently as possible while maintaining acceptable residual volumes (ie, less than 200 to 300 mL). Patients are typically unable to tolerate more than three to four catheterizations per day.

●Indwelling bladder catheter – Placement of an indwelling bladder catheter can be used for bladder decompression while the underlying cause of lower tract obstruction is addressed. However, this option is associated with a higher risk of urinary tract infection compared with clean intermittent catheterization [7].

●Indwelling suprapubic cystostomy tube – Placement of an indwelling suprapubic cystostomy tube is appropriate in patients with lower tract UTO in whom placement of a transurethral catheter is not possible (eg, benign or malignant urethral stricture, severe extrinsic urethral compression due to prostatic hypertrophy or a mass lesion). This technique is also associated with a higher risk of infection and [7], in addition, may cause bleeding and damage to surrounding structures, including blood vessels. Cystostomy tubes can be placed by palpation of bladder at the bedside, with local anesthesia if necessary. Alternative approaches include use of transabdominal ultrasound or cystoscopic guidance with placement of a guidewire percutaneously into the bladder to guide passage of the tube.

After decompression of the bladder, patients should be reimaged (eg, with kidney and bladder ultrasound) after one to two weeks, or sooner if symptoms and/or signs of obstruction do not resolve.

If hydronephrosis persists despite bladder drainage, upper tract obstruction may also be present. If symptoms and/or signs of obstruction remain after bladder decompression (eg, continued pain, nonresolving azotemia), then it should be assumed that the persistent hydronephrosis represents upper tract obstruction. (See 'Upper tract obstruction' below.)

Conversely, hydronephrosis may remain for varying periods of time after resolution of obstruction, particularly if the obstruction was chronic. Some patients will have permanent dilation of the collecting system. Thus, if the patient's symptoms and signs of UTO resolve after bladder decompression, then residual hydronephrosis may not be clinically important. If it is unclear whether or not the patient has persistent obstruction, a functional mercaptoacetyltriglycine (MAG-3) renal scan, ideally with a diuretic wash-out to calculate a half-life excretion time, can help differentiate.

Upper tract obstruction — Relief of obstruction in patients with upper tract UTO is achieved with anterograde placement of a PCN or PCNU or retrograde placement of a ureteral stent. Once the obstruction is relieved, the underlying cause should be corrected, if possible. (See 'Treating the underlying cause of UTO' below.)

Preprocedural management

●Preoperative antibiotics – Patients with UTO complicated by a suspected urinary tract infection require prompt therapy (ie, within one hour) using broad-spectrum antibiotics that cover pseudomonas, other gram negative bacteria, and methicillin-resistant Staphylococcus and Enterococcus (table 2 and algorithm 1). The choice of specific agents and the rationale are presented separately. (See "Acute complicated urinary tract infection (including pyelonephritis) in adults and adolescents", section on 'Empiric antimicrobial therapy'.)

In patients without suspected urinary tract infection, prophylactic antibiotics are given prior to the procedure (table 3). This issue is discussed in other topics. (See "Percutaneous nephrostomy tubes", section on 'Insertion techniques' and "Placement and management of indwelling ureteral stents", section on 'Stent placement'.)

●Management of antiplatelet and anticoagulant medication – Antiplatelet agents and anticoagulant drugs do not generally need to be discontinued or reversed prior to cystoscopic ureteral stent placement. Conversely, the risk of bleeding is higher with PCN and PCNU. Thus, cystoscopic stent placement is generally preferred in anticoagulated patients. If placement of a PCN or PCNU is necessary, anticoagulation should be reversed first.

Preoperative reversal of anticoagulation is appropriate for some patients before cystoscopic stent placement. As examples, anticoagulated patients with a significant tumor burden in the bladder or those with marked prostate enlargement may develop gross hematuria during the procedure, leading to diminished visualization and difficulty placing the stent.

●Procedural considerations – Cystoscopic ureteral stents are typically placed under general anesthesia. Thus, patients who should not undergo general anesthesia (eg, septic patients or those with severe electrolyte abnormalities) typically undergo PCN or PCNU placement, which can be performed with local anesthesia and without sedation.

Because rigid cystoscopy requires that the patient be in the dorsal lithotomy position, the procedure may be difficult for patients with certain orthopedic hip surgeries or patients with significant musculoskeletal contractions. In such patients, a PCN or PCNU is preferable. Although flexible cystoscopy in males may be performed in the supine position and stent placement is often feasible, visualization is not as optimal as with rigid cystoscopy. Flexible cystoscopy may also be performed in female patients, but this requires the frog-leg position, which is subject to the same musculoskeletal limitations as the dorsal lithotomy position. Ureteral stent placement may be attempted through a percutaneous cystostomy tract, but this procedure is technically difficult, and the risk of bleeding and damage to surrounding structures is greater than with the transurethral approach.

Placement of a PCN (or PCNU) requires that the patient be able to tolerate the prone position for approximately 30 minutes (or 60 minutes if both kidneys require decompression), although this varies depending upon technical difficulty. In patients who cannot tolerate the prone position for the duration of the procedure, such as those with difficult airways or severe respiratory distress, those with healing or open chest or abdominal wounds or incisions, or those who have severe obesity, a cystoscopic approach may be preferred.

Before cystoscopic stent placement, PCN, or PCNU, the bladder should be decompressed if there is any concern for incomplete emptying. In addition, hyperkalemia and metabolic acidosis should be addressed, if necessary. (See "Treatment and prevention of hyperkalemia in adults" and "Approach to the adult with metabolic acidosis".)

The technical aspects of cystoscopic ureteral stent placement and placement of PCNs and PCNUs are presented in detail separately. (See "Placement and management of indwelling ureteral stents" and "Percutaneous nephrostomy tubes".)

Approach to urgent upper tract obstruction — Relief of obstruction in patients with upper tract UTO is achieved with anterograde placement of a PCN or PCNU or retrograde placement of a ureteral stent. The choice between these procedures is informed by the clinical setting:

●Patients with urosepsis (or impending sepsis due to urinary tract infection) – Patients with urosepsis in the setting of upper tract UTO should undergo PCN if time allows, rather than cystoscopic ureteral stent placement. Although cystoscopic stent placement can typically be performed more quickly than PCN, general anesthesia is usually needed for cystoscopic stent placement; this is generally unsafe in septic patients. In addition, it is not possible to know whether or not retrograde ureteral access will be successful until the procedure begins. If, for example, there are ureteral strictures that not amenable to dilation or if visualization of the ureteral orifices is obscured by tumor or gross hematuria, then relief of obstruction will be delayed, which is dangerous in an emergency setting. In contrast to cystoscopic stent placement, insertion of a PCN can be performed without general anesthesia or monitored anesthesia care, and relief of obstruction can usually be achieved with greater frequency as compared with cystoscopic stent placement.

PCN is preferred over PCNU in the emergency setting since the additional manipulation required for stent placement may increase bacterial transfer into the bloodstream and may exacerbate septic physiology [8,9]. However, following resolution of infection, the PCN can be converted to a nephroureteral stent.

●Patients with acute kidney injury and/or hyperkalemia – In patients with AKI and/or hyperkalemia, relief of obstruction is urgent and, for the same reasons as described for patients with urosepsis, placement of a PCN or PCNU is often preferred over an attempt at cystoscopic stent placement. Those patients with a hyperkalemic emergency should be treated medically (eg, rapidly acting therapies, gastrointestinal cation exchanger) but relief of the obstruction should generally not be delayed in order to perform hemodialysis. AKI and hyperkalemia as a result of UTO typically resolve quickly with relief of the obstruction and hemodialysis can often be avoided.

However, some clinicians would start with a cystoscopic approach in these patients, particularly if the AKI is nonsevere and the hyperkalemia is mild.

●Patients with prior surgical alteration of the urinary tract (eg, kidney transplant, bladder or ureteral surgery) – Patients with a history of surgical alterations of the urinary tract and who require urgent relief of obstruction should generally undergo PCN or PCNU placement, rather than an attempt at retrograde cystoscopic ureteral stent placement. For cystoscopic stent insertion to be successful, an access wire must traverse the ureteral orifice and ureter. Thus, when there is significant doubt about feasibility of retrograde stent placement in an urgent situation, it best to consult with interventional radiology or interventional nephrology regarding an anterograde percutaneous procedure.

Patients who have undergone radical cystoprostatectomy have uretero-enteric anastomoses that generally preclude urgent retrograde access [10]. Patients who are status post ureteral reimplantation or kidney transplantation have a heterotopic ureteral orifice that may make retrograde ureteral stent insertion challenging or even impossible. Cross-trigonal ureteral reimplantation presents challenging anatomy due to the acute angle of the ureterovesical junction [11,12]. Even if retrograde access can be obtained in a patient with a kidney transplant, the ureteral length is short and often the standard stents are long and may predispose to dislodgement of the stent.

In general, percutaneous access to the transplant renal collecting system can be readily and safely accomplished using a combination of ultrasound and fluoroscopic guidance. PCN placement may be performed, or if the ureteral stricture can be readily traversed, a PCNU can be placed. Patients with anastomotic strictures can be managed as described below; if the stricture is successfully remodeled, the PCN can eventually be removed [13].

●Patients with suspected obliterative ureteral lesions – In the urgent setting, PCN or PCNU is preferred over retrograde stent placement in patients with suspected obliterative ureteral lesions. Such patients include those with large and impacted ureteral stones or obliterative ureteral strictures. It may be difficult or impossible to traverse an access wire past the obstruction in these settings. Similar to patients with surgical alterations of the urinary tract noted above, any doubt about the feasibility of retrograde stent placement in an urgent setting favors an anterograde approach.

●Malignant ureteral obstruction – Similarly, in patients with primary or invasive ureteral tumors or ureteral obstruction due to extrinsic compression by a tumor, PCN or PCNU is preferred in the urgent setting over retrograde stent placement. In addition to the difficulty traversing a wire across the obstruction, ureteral stents have a relatively high failure rate among such patients [14].

●Patients with gross hematuria or those prone to urinary tract bleeding – Gross hematuria can obscure the ureteral orifices and thereby cause difficulty in retrograde passage of an access wire for stent placement. Thus, such patients who need urgent relief of obstruction are typically treated with PCN or PCNU placement.

Patients with luminal malignancy obstructing the ureter or those who have conditions associated with bleeding from the bladder wall (eg, hemorrhagic cystitis or malignant bladder masses) may be at increased risk of hemorrhage due to irritation or erosion by a ureteral stent [15]; in such patients, PCN may be the best option.

●Patients with coagulopathy or who are anticoagulated – As noted above, the risk of significant bleeding is high with percutaneous placement of a tube or stent among anticoagulated patients and those with coagulopathy. Thus, a cystoscopic approach is preferred in such patients. However, if PCN or PCNU is deemed necessary for the reasons listed above, anticoagulation should first be reversed.

●Other considerations – In patients without one of the above reasons to select one procedure over the other, additional factors weigh in the decision of how to relieve the obstruction:

•Painful bladder syndromes – Some patients may have more difficulty tolerating an indwelling ureteral stent. Since stents typically have curled proximal and distal ends (ie, pigtails) to limit stent migration (picture 1), part of the stent permanently resides in the bladder. This may exacerbate symptoms of painful bladder syndrome or interstitial cystitis in patients with these conditions.

•Risk of rapid stent encrustation – Patients who are prone to kidney stone formation may suffer from rapid encrustation of indwelling ureteral stents, leading to stent dysfunction [16]. Some, but not all, data suggest that stent encrustation also occurs more frequently in pregnant people due to physiologic hypercalciuria of pregnancy [17-19].

•Concern that the patient cannot or will not follow up – Even among patients not prone to stone formation, stent encrustation eventually occurs, and the resulting stent dysfunction can lead to kidney damage [20]. Thus, stents need to be removed or exchanged; for patients who require a long-term indwelling stent, exchange is typically performed every three to six months. If there is concern that the patient will be unable to return for stent removal or exchange, PCN or PCNU is generally preferred. Although a PCN or PCNU also requires preventative maintenance (on a similar schedule), encrustation of these catheters is simpler to manage than encrustation of an indwelling stent. In addition, patients with a PCN or PCNU have an external catheter and drainage bag and therefore typically return for follow-up. Conversely, patients with an indwelling stent can forget and may require lithotripsy or surgery to remove a severely encrusted stent.

•Quality of life – A percutaneous nephrostomy catheter sits proximal to the site of obstruction and therefore must drain externally to a drainage bag. From a quality of life perspective, patients often prefer an indwelling ureteral stent since no external collection bag is necessary [21,22]. This allows for greater freedom of movement and the ability to fully submerge in a body of water. In addition, the risk of urinary tract infection is mitigated with an indwelling ureteral stent compared with a nephrostomy tube, and indwelling stents have a lower likelihood of becoming dislodged.

However, if a PCNU is inserted (rather than a PCN), the catheter allows urine to pass via side holes from the renal collecting system to the bladder, bypassing the site of obstruction if it is within the ureter. Urine can drain internally to the bladder as well as externally to a drainage bag. Then, following acute decompression of the collecting system, the external portion of the catheter may be capped to allow for internal drainage to the bladder only, thereby eliminating the need for an external drainage bag [23,24].

In addition, patients who were initially managed with a PCN will often be candidates for subsequent conversion to a PCNU or internal double-J stent. In order for this to be possible, it must be technically feasible to place a guidewire across the site of ureteral obstruction and into the bladder, and the area of obstruction must be distensible enough to allow passage of a stent. Balloon dilation of the ureter may be required to permit stent passage [25]. Some obstructions cannot be traversed, such as in patients with bulky retroperitoneal lymphadenopathy or muscle invasive bladder malignancy, so nephrostomy may be the only option.

WHEN RELIEF OF OBSTRUCTION IS NONURGENT — As noted above, treatment of the underlying cause of obstruction can be the initial approach when relief of obstruction is not urgent. A nonurgent setting is defined by all of the following:

●Unilateral UTO (in a patient with two kidneys)

●Normal kidney function

●No concerning electrolyte abnormalities

●No evidence of urinary tract infection

When relief of obstruction is not urgent, the management depends upon the cause of obstruction (table 1). (See 'Treating the underlying cause of UTO' below.)

In some patients with UTO, the underlying cause of obstruction may not be quickly reversible or may not be reversible at all. In such patients, it is appropriate to place a percutaneous nephrostomy tube (PCN), percutaneous nephroureteral stent (PCNU), or cystoscopic ureteral stent while attempting to address the cause of obstruction.

TREATING THE UNDERLYING CAUSE OF UTO — UTO may occur at the level of the kidney, ureter, bladder, or urethra (table 1).

●Kidney stone – A kidney stone is the most common cause of UTO. Treatment of an obstructing stone depends upon the size of the stone and could include surgical intervention, extracorporeal shock-wave lithotripsy, medical expulsive therapy, or supportive measures only (algorithm 2). (See "Kidney stones in adults: Surgical management of kidney and ureteral stones" and "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis".)

●Prostatic hypertrophy – Prostatic hypertrophy is a common cause of bladder outlet obstruction. Management of this condition is presented separately. (See "Medical treatment of benign prostatic hyperplasia" and "Surgical treatment of benign prostatic hyperplasia (BPH)".)

●Bladder dysfunction – Treatment of bladder dysfunction depends upon the etiology of the dysfunction. (See "Chronic complications of spinal cord injury and disease", section on 'Urinary complications' and "Manifestations of multiple sclerosis in adults", section on 'Bowel and bladder dysfunction' and "Diabetic autonomic neuropathy", section on 'Bladder dysfunction' and "Chronic urinary retention in females", section on 'Detrusor underactivity'.)

●Ureteral strictures – Patients with UTO due to a ureteral stricture are temporarily managed with placement of either an indwelling ureteral stent or PCN as a bridge to definitive repair. Options for definitive repair of discrete ureteral strictures include ureteral reimplantation or ureteroureterostomy. For more severe ureteral strictures, other options include ileal ureteral transposition or kidney auto-transplantation. The decision for definitive repair is based on surgical candidacy, perioperative risk, and the underlying etiology of upper tract obstruction. As an example, patients whose stricture resulted from previous radiation therapy may be at a higher risk for complications following ureteral reconstruction. A ureteral stent or PCN can be permanent in select patients who are poor candidates for definitive surgical repair.

Alternatively, there are endoscopic options for poor surgical candidates, such as ureteral dilation with followers, controlled balloon dilation, or laser incision of the ureteral stricture; these procedures are followed by stent placement. However, these procedures have lower success rates than definitive surgical reconstruction. In addition, there is a risk of urine leak/urinoma following endoscopic intervention despite the postoperative insertion of an indwelling stent.

Postsurgical anastomotic ureteral strictures can be treated using interventional radiology techniques. This is most commonly accomplished by achieving percutaneous access to the kidney and traversing the stricture antegrade with an angled tip catheter and guidewire. The stricture is then dilated with a balloon catheter, and a relatively large caliber nephroureteral catheter (often up to 16 French) is placed across the site. The catheter is left in place for six weeks to allow the strictured segment to "remodel" around it. The patient then returns for an over-the-wire nephrostogram to assess the stricture site. If the ureter is patent and with brisk flow across it, the catheter can be converted to a percutaneous nephrostomy to maintain access to the collecting system and capped to allow urine to pass via the ureter only. The patient then returns two weeks later for a nephrostogram, and if the ureter remains patent, the nephrostomy can be removed. The procedure is performed in this stepwise fashion since strictures do not always remodel effectively following balloon dilation and may recur following ureteral stent removal. Since stricture dilation is sometimes unsuccessful, it is best to initially maintain access to the collecting system to allow for additional imaging and potential reversion to long-term ureteral stenting, if necessary.

Sometimes, patients with an ileal neobladder (following urinary diversion for cystectomy) may develop an anastomotic ureteral stricture. Percutaneous access to the renal collecting system can be established and an angled-tip catheter and guidewire advanced through the stricture and neobladder and out of the urostomy under fluoroscopic guidance. A ureteral stent can then be advanced retrograde over the wire to the renal pelvis. Percutaneous wire access to the kidney is then removed, leaving a catheter that allows urine to pass from the renal pelvis, traversing the ureter and neobladder and ending within the urostomy bag. The catheter can be readily changed at three-month intervals to prevent encrustation and occlusion [26].

●Kidney papillary necrosis (sloughed papilla) – Rarely, UTO may be caused by kidney papillary necrosis with sloughing of a papilla that impairs urine passage into the ureter or becomes lodged in the ureter. Risk factors for papillary necrosis include sickle cell disease, diabetes mellitus, analgesic nephropathy, and kidney infections (eg, pyelonephritis, tuberculosis) [27,28]. Relief of the obstruction is usually achieved with a ureteral stent and prevention of further obstruction depends upon management of the underlying etiology.

●Blood clot – Patients with gross hematuria as a result of bleeding from the kidney, ureter, or bladder may develop obstruction as a result of a blood clot [29,30]. Control of the hemorrhage can often be achieved with endoscopic fulguration, selective renal artery embolization, or, if intractable, nephrectomy. If source control of the bleeding is successful, the clot can be removed endoscopically followed by placement of a ureteral stent.

●Ureteral or urothelial carcinoma – Patients with ureteral or urothelial carcinoma typically undergo surgical (eg, nephroureterectomy in those with ureteral carcinoma) and treatment with chemotherapy. These disorders are discussed elsewhere. (See "Malignancies of the renal pelvis and ureter" and "Overview of the initial approach and management of urothelial bladder cancer".)

●Endometriosis or pelvic organ prolapse – Patients with advanced pelvic endometriosis may be managed with indwelling ureteral stents or a PCN, pending definitive surgical repair. Urologic intervention may be warranted for reconstruction in the rare circumstance of direct bladder or ureteral involvement that requires resection.

Pelvic organ prolapse due to cystocele may cause distal occlusion, or "kinking," of the ureterovesical junction. This may cause ureteral stent placement to be challenging due to aberrant bladder trigonal anatomy. In this setting, anterior vaginal wall digital compression can be performed at the time of cystoscopy, which may straighten the ureterovesical junction angle sufficiently to permit successful placement of a stent. Definitive repair of cystocele may also address the underlying ureteral obstruction.

●Retroperitoneal fibrosis – In patients who require urgent relief of obstruction, PCN, ureteral stent placement, or surgery is an option. For those who do not need an urgent procedure, pharmacologic treatment of the RPF is initiated and the imaging is repeated after several weeks, to assess for resolution. Treatment of patients with retroperitoneal fibrosis and UTO is presented in detail separately. (See "Treatment of retroperitoneal fibrosis", section on 'Treatment of urinary obstruction'.)

●Extrinsic ureteral compression from lymphadenopathy or tumor – Ureteral obstruction in this setting may be temporarily managed with either indwelling ureteral stents or nephrostomy tubes, while awaiting definitive therapy. In these situations, retrograde stent placement may not be technically feasible. Even if it is accomplished, small caliber stents placed via cystoscope may fail due to compression. Thus, percutaneous nephrostomy may be the best option for decompression. However, sometimes, larger caliber nephroureteral stents can be used to allow for internal drainage to the bladder with the catheter capped externally [31].

ONGOING MANAGEMENT OF OBSTRUCTION — Patients who need ongoing management of obstruction with an indwelling stent, a percutaneous nephrostomy tube (PCN), or a percutaneous nephroureteral stent (PCNU) should have follow-up imaging to evaluate for persistent obstruction and will need periodic exchange procedures.

●Evaluating for persistent obstruction – In patients with upper tract obstruction who are treated with an indwelling ureteral stent or nephrostomy, follow-up imaging (with kidney and bladder ultrasound or abdominal computed tomography [CT]) should be performed at approximately six weeks to evaluate for persistent obstruction. In particular, patients with malignant ureteral obstruction are at a relatively high risk for indwelling ureteral stent or PCNU failure leading to persistent UTO [14].

Persistent hydronephrosis evident on follow-up imaging could be due to persistent UTO or to retrograde urine reflux due to bladder pressure. Retrograde reflux of urine typically does not cause kidney damage and does not need to be addressed, whereas persistent UTO requires intervention. To differentiate between persistent UTO and retrograde urine reflux due to bladder pressure, the patient should undergo a dynamic MAG-3 renal scan. Placement of a bladder catheter during the procedure may prevent reflux during the examination and therefore aid in the interpretation of the MAG-3 scan, although this is controversial.

●Exchange of stents and nephrostomy catheters – Traditional indwelling ureteral stents are generally exchanged every three months to avoid encrustation, although some models can dwell for a longer duration. The long-term management of indwelling ureteral stents is presented separately. (See "Placement and management of indwelling ureteral stents", section on 'Stent exchange/removal'.)

PCN and PCNU also require over-the-wire exchange at approximately three-month intervals for preventive maintenance, to prevent encrustation and occlusion. Some patients may develop encrustation earlier, so more frequent catheter exchanges may be necessary [19]. This is discussed in detail elsewhere. (See "Percutaneous nephrostomy tubes", section on 'Maintenance'.)

COMPLICATIONS

Complications of indwelling ureteral stents — Complications of indwelling ureteral stents include:

●Irritative lower urinary tract symptoms – This is the most common complication of indwelling ureteral stents. This issue and its treatment are presented separately. (See "Placement and management of indwelling ureteral stents", section on 'Irritative symptoms' and "Placement and management of indwelling ureteral stents", section on 'Pain management'.)

●Gross hematuria. (See "Placement and management of indwelling ureteral stents", section on 'Hematuria'.)

●Urinary tract infection. (See "Placement and management of indwelling ureteral stents", section on 'Urinary tract infection'.)

●Stent encrustation. (See "Placement and management of indwelling ureteral stents", section on 'Stent encrustation'.)

●Stent migration. (See "Placement and management of indwelling ureteral stents", section on 'Stent migration'.)

●"Forgotten" stent. (See "Placement and management of indwelling ureteral stents", section on 'Retained stent'.)

●Ureteral or calyceal perforation – Placement of ureteral stents may be complicated by ureteral or calyceal perforation, which can lead to bleeding, retroperitoneal hematoma, or ureteral stricture.

Complications of percutaneous drainage catheters (PCN and PCNU) — The most important complications of PCN or PCNU placement are infection and hemorrhage. These issues are discussed elsewhere. (See "Percutaneous nephrostomy tubes", section on 'Major complications'.)

In addition, patients may experience catheter dislodgement, malposition, and occlusion, and these issues are unfortunately fairly common. If a catheter is inadvertently pulled out, the patient should return to interventional radiology urgently to allow for potential replacement via the existing percutaneous track. This becomes increasingly difficult to accomplish as time from dislodgement increases, as the tracks tend to close over time. If a track cannot be recanalized, placement via new percutaneous access will be required, which is a more difficult procedure and poses greater risk. Catheters that are malpositioned or occluded tend to present with pericatheter leakage and flank pain. (See "Percutaneous nephrostomy tubes", section on 'Minor complications'.)

Any of these issues should prompt evaluation for possible catheter exchange [8,32].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Acute kidney injury in adults".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Acute kidney injury (The Basics)" and "Patient education: Hydronephrosis in adults (The Basics)")

SUMMARY AND RECOMMENDATIONS

●General principles – Urinary tract obstruction (UTO) can be caused by (table 1) (see 'General principles' above):

•Lower tract obstruction – Lower tract obstruction is caused by bladder dysfunction or bladder outlet obstruction. These patients present with an elevated postvoid residual and, typically, bilateral hydronephrosis (unilateral hydronephrosis should raise suspicion for upper tract [ie, supravesicular] obstruction).

•Upper tract obstruction – Upper tract obstruction is due to problems in the ureters or kidneys. These patients present with either unilateral or bilateral hydronephrosis. In patients with bilateral hydronephrosis, upper tract obstruction should be suspected if the postvoid residual is normal or the hydronephrosis persists despite bladder decompression.

●Determining the urgency of treatment – In some instances, UTO is considered an emergency or urgency, and should be relieved as soon as possible (see 'Determining the urgency of treatment' above):

•Emergencies (obstruction should be relieved within several hours):

-Urosepsis (or signs of impending sepsis due to urinary tract infection)

-Severe metabolic abnormalities (eg, hyperkalemia)

•Urgencies (obstruction should be relieved within 24 hours):

-Acute kidney injury (AKI)

-Bilateral UTO or obstruction of a single functioning kidney

•Emergency or urgency not present:

Among other patients with UTO, those who have one or more of the following should also have the obstruction relieved promptly, although these are not considered emergencies or urgencies:

-Severe chronic kidney disease or kidney impairment of unclear duration

-Severe symptoms attributable to the obstruction (eg, unyielding pain)

While not emergent or urgent indications, it is still advisable to relieve obstruction as soon as practical in such patients. Sustained obstruction can lead to irreversible loss of kidney function.

Unlike in the patients just described, the underlying cause of obstruction can often be addressed first (without the need to first perform nephrostomy tube or stent placement) among those who meet all of the following criteria:

-Unilateral UTO (in a patient with two kidneys)

-Normal kidney function or nonsevere chronic kidney disease

-No concerning electrolyte abnormalities

-No evidence of urinary tract infection

●Management of a UTO emergency or urgency – In patients with a UTO emergency or urgency, an interventional procedure is performed; options depend upon the level of obstruction:

•Lower tract obstruction – Bladder decompression is necessary in this setting. In such patients, we suggest clean intermittent catheterization rather than placement of an indwelling bladder catheter (Grade 2C). (See 'Lower tract (bladder) obstruction' above.)

•Upper tract obstruction – In patients with upper tract obstruction, treatment options include percutaneous placement of a nephrostomy tube (PCN) or nephroureteral stent (PCNU), or retrograde cystoscopic placement of a ureteral stent. The choice between these procedures depends upon many factors, including whether or not the patient can safely undergo general anesthesia, the suspected cause of obstruction, whether or not there are anatomical alterations to the urinary tract, the presence of gross hematuria, anticoagulation, as well as several other factors. These issues are discussed above. (See 'Upper tract obstruction' above.)

After the obstruction is relieved, the underlying cause of the obstruction should be corrected (table 1). This is presented below. In some cases, the cause of obstruction (eg, kidney stone) can be addressed during the same procedure. (See 'Treating the underlying cause of UTO' above.)

●Management when relief of obstruction is nonurgent – If relief of obstruction is not an emergency or urgency, then treatment of the underlying cause of obstruction can be the initial approach (table 1). (See 'Treating the underlying cause of UTO' above.)

In some such patients, the underlying cause of obstruction may not be quickly reversible or may not be reversible at all. In such patients, placement of a PCN, PCNU, or cystoscopic ureteral stent is often appropriate while attempting to address the cause of obstruction.

●Ongoing management – Patients who need ongoing management of obstruction with an indwelling stent, a PCN, or a PCNU should have follow-up imaging to evaluate for persistent obstruction and will need periodic exchange procedures. (See 'Ongoing management of obstruction' above.)

•In patients with upper tract obstruction who are treated with an indwelling ureteral stent or nephrostomy, follow-up imaging (with kidney and bladder ultrasound or abdominal computed tomography [CT]) should be performed at approximately six weeks, to evaluate for persistent obstruction.

•Traditional indwelling ureteral stents are generally exchanged every three months to avoid encrustation, although some models can dwell for a longer duration. PCN and PCNU also require over-the-wire exchange at approximately three-month intervals for preventive maintenance.