Obstructive Uropathy

Etiology

There are a significant number of potential causes of obstructive uropathy, and these vary widely. However, the most frequently diagnosed cause is benign prostatic hypertrophy or hyperplasia.  Although not particularly common, other potential causes include constipation, urethral strictures, phimosis or paraphimosis, prostatic adenocarcinoma, retroperitoneal adenopathy, colonic endometriosis, ureterocele, urolithiasis, and neuropathic bladder dysfunction, parasitic obstructions, bladder endometriosis, and urate nephrolithiasis.[1][2][3][4][5][6] The history and physical examinations are key in the diagnosis of the underlying cause.  Obstructive uropathy can also present in the neonatal period, prompting evaluation for genitourinary tract dilatation and vesicoureteral reflux and highlighting the importance of intrauterine fetal anatomy ultrasounds.[7]

Epidemiology

Urinary obstruction affects all age groups, but the majority of cases present in the bimodal distribution in infants and the elderly. Congenital genitourinary tract abnormalities (e.g., posterior urethral valves) present in childhood as urinary obstruction, producing an estimate of approximately 4% of the total cases.[8] The largest group is made up of people over 60 and more frequently males due to the anatomic presence of prostate (benign prostatic hyperplasia and cancers). Symptoms of urinary retention occur in up to 1% to 2% of men with BPH per year.[9] Obstructive uropathy is significantly less common in females.

Pathophysiology

When there is a restriction to the normal flow of urine through the urinary tract, there will be a back pressure of urine into the collecting system of the kidneys. In time, this may produce dilatation within the tract, and as the kidneys filtration system becomes affected, it becomes the primary reason for the development of obstructive nephropathy. The mechanism of nephropathy, in this case, involves many factors, including local ischemia due to distention and increased intratubular pressures.  In a partial obstruction, angiotensin and AT1-receptor appear to be upregulated, increasing ureteral peristalsis to help relieve the obstruction.[10]

While peristaltic function may be of benefit in a partial obstruction, it is likely to cause increased distention and intraluminal pressures when the obstruction is complete. Rat models have also demonstrated influence from the renin-angiotensin-aldosterone axis, and TGF-beta1 expression was markedly increased in hydronephrotic kidneys, which may occur in humans as well, but further studies are needed.[11] These factors may lead to irreversible damage to the kidney, but it is difficult to predict the time and rate at which this will occur. This highlights the importance of early identification and treatment of the underlying obstruction.

Histopathology

Obstructive uropathy may lead to a reduced glomerular number, glomerular hyalinization, cortical cysts, and interstitial inflammation within the kidney.[12] It is believed these histopathological changes are secondary to an inflammatory process.[13]

History and Physical

The severity of symptoms and likely even the number of symptoms present are influenced by the degree, location, and time from the onset of the obstruction. The presence of pain is common in urinary tract obstructions. Patients may present with abdominal and/or flank pain. The location, quality, severity, and modifying factors of the discomfort may help to aid in determining the location and underlying cause. For example, dull flank pain with sharp radiation into the lower quadrant or groin may suggest ureterolithiasis as the underlying cause of obstruction.

Nocturia, dysuria, urinary urgency or frequency, and decreased force of urinary stream should suggest benign prostatic hypertrophy/hyperplasia or prostatic adenocarcinoma. Fever should increase your concern for concomitant urinary tract infection and, possibly, septicemia. Prostatic malignancy should be considered in the presence of recent unintentional weight loss, night sweats, and hematuria with a nodular prostate on examination. Radiation and other treatments for prior malignancies can increase scarring in the GU tract and produce obstruction. Gastrointestinal symptoms of constipation, nausea, vomiting, and diarrhea may aid in diagnosing fecal impaction, bowel obstruction, or a colonic mass as contributing factors to the urinary tract obstructions. Recent surgeries (e.g., appendectomy, hysterectomy) can suggest ureteral injury. As evidenced above, providers must perform a complete history and a thorough review of systems.

A complete examination should be performed, focusing on the abdomen and genitalia. The presence of a distended bladder should direct the clinician to the possibility of urinary retention. A digital rectal examination may reveal prostatic enlargement or fecal impaction. An assessment of strength, sensation, reflexes, and muscle tone can be informative. A thorough history and physical examination will often point towards the underlying etiology.

Evaluation

A basic metabolic panel should be performed in most patients with evidence of obstructive uropathy, with a specific focus on the patient's renal function. Urinalysis should be performed to rule out urinary tract infection. Urine protein-to-creatinine ratio and urine electrolytes may be beneficial for guiding further care. A bedside ultrasound should be performed to quickly assess the bladder volume and the severity of hydronephrosis. Ultrasound is the most readily available and least invasive test. A comprehensive ultrasound can also be performed for further assessment. The next radiographic test to be considered for most providers would be a CT of the abdomen and pelvis, especially if there is a concern for intra-abdominal pathologies, such as tumors. Additional testing to be considered in specific circumstances would be intravenous pyelogram, voiding cystourethrogram, and renal nuclear scans.  MRI can also be considered.

Treatment / Management

Electrolyte abnormalities should be corrected, as indicated. If renal function is significantly worse from baseline, or there are significant electrolyte abnormalities, hospital admission and urgent nephrology consultation may be warranted. Urinalysis is likely to be performed to rule out infection, and antibiotics should be prescribed as indicated. Urine samples are often also sent for culture.

The treatment of obstructive uropathy is based around promptly addressing the obstructive process. Bladder volume measurements can help to guide further therapies from this point. A Foley catheter is likely to be attempted, particularly if the obstruction is due to the most frequent etiology, benign prostatic hypertrophy, or hyperplasia.[14] The initial attempt usually occurs with a 16- or 18-Fr Foley. The presence of obstruction may prevent the initial success of urethral catheterization and may require higher-level interventions. The most typical next step would be a trial of urethral catheterization using a Coudé tip Foley, but more significant interventions may be required and are addressed in other articles.[15][16][17] 

While unlikely, suprapubic catheterization or cystostomy may be required for cases when urethral catheterization is not feasible. The duration of time the Foley should be in place is based on a combination of the initial bladder volume and post-catheterization residual. This decision often occurs in conjunction with a urologist. Outpatient follow-up with urology should be arranged as they will play a significant role in determining the need for and guiding long-term therapies. The Foley catheter will be removed at the discretion of the urologist at follow-up. Infrequently, individuals may fail the trial without a catheter, resulting in the replacement of the catheter. At this point, additional interventions may be indicated, including ureteral stents, drains, or placement of nephrostomy tubes. There may be a potential benefit of more invasive procedures for the management of obstructions that fail more conservative management, and these include prostate artery embolization.[18]

There are certain cases where medication therapies may be pursued. Medications that inhibit alpha-1-adrenergic receptors (e.g., tamsulosin, terazosin), which result in relaxation of the smooth muscle within the bladder neck and prostate, have been indicated to improve symptoms of urinary obstructive secondary to BPH. Tamsulosin demonstrated having a positive effect for moderate to severe obstructive symptoms due to benign prostatic hypertrophy.[19] While orthostasis is a commonly cited concern with the use of this medication, several studies have suggested the absence of any significant side effects.[20][21] Bicalutamide and leuprolide, which act via antiandrogen and luteinizing hormone agonism, respectively, may help to relieve obstruction by shrinking the prostate.[22][23][24] (A1)

Finasteride and dutasteride are each FDA-approved for the treatment of BPH. These medications act by inhibiting the 5-alpha-reductase enzyme, blocking the conversion of testosterone to dihydrotestosterone, and reducing prostate size.[25] Several of these medical therapies may be combined and are likely to produce a synergistic effect.(A1)

Management of nephropathy due to obstruction also begins with relieving the urinary tract obstruction, but is an entire topic in itself and will not be discussed further here.

Differential Diagnosis

Differential diagnoses are broad and dependent on location, timing, and risk factors. A detailed history and thorough physical examination allow for inclusion, or exclusion, of differentials. The presence of urinary retention may be secondary to an obstruction, infection, medication side effect, neurogenic, secondary to spinal cord impingement, detrusor muscle dysfunction, and may also be acute or chronic in nature.[26] 

Fever or other constitutional symptoms can point towards infectious etiologies, such as pyelonephritis or spinal epidural abscess. Unilateral flank pain and known renal stone disease could indicate obstruction from ureterolithiasis. Prior urologic instrumentation procedures should lead the provider to consider urethral strictures or blood clots as a cause of obstruction. The presence of neurologic deficits should prompt evaluation for stroke or spinal cord diseases.

History of intravenous drug use can suggest epidural abscess or discitis. The presence of malignancy raises suspicion for spinal cord or vertebral metastases. Aortic aneurysm or dissection should be considered as a cause of flank pain in a patient with a history of hypertension and smoking. Constipation or the presence of a fecal impaction could produce obstruction in the urinary tract.  Medication changes or recent anesthetic events may lead to symptoms of retention. As with all patient presentations, history and physical examination will guide your differential diagnoses and diagnostic workups.

Prognosis

Prognosis depends on the underlying etiology of the obstruction.  An acute urologic obstruction is more likely to be reversible and less likely to produce damage to the kidney filtration system or other functions. However, chronic obstruction produces worse long-term effects on renal function. The development of chronic renal problems is less likely if only one of the kidneys is affected by the initial obstructive process. Although uncommon after the resolution of acute obstruction, if renal dysfunction persists or worsens, long term outlook could include the need for hemodialysis or renal transplant. The overall prognosis worsens if concomitant UTIs remain untreated.

Complications

Complications are often the result of the underlying cause, and management of these vary on a case-by-case basis. However, as mentioned above, an obstruction can lead to permanent damage and possibly failure of the kidneys. Again, while this is less likely to occur during an acute obstruction, it remains possible, and the likelihood increases if the obstruction is chronic. It is especially important to recognize signs of obstruction in fetuses and neonates, as it is the leading cause of renal failure and would cause significant long-term morbidity and mortality for the child.[7] For children with chronic renal failure, obstructive uropathy was felt to be accountable for 16.5% of all pediatric renal transplants.[27] 

The identification of these issues in utero can improve the overall outlook for these children, highlighting the importance of the anatomic fetal ultrasound.[28] Obstructive uropathy has been suggested to increase the likelihood of urinary tract infections, but UTI may also be the first sign of obstruction.[29] 

Microscopic hematuria is common following urethral catheterization, but more significant bleeding can occur, and these would require intervention (possibly continuous bladder irrigation through a 3-way Foley). Transient hypotension and bradycardia may occur after placement of the Foley but generally resolves with observation alone.

Previously, it was thought that the bladder should be drained more gradually due to hypotension, but more recent studies have demonstrated no significant difference in outcomes between rapid and gradual drainage.[30]  Postobstructive diuresis, which is addressed further in a separate article, may occur, and these patients may benefit from hospital observation for close monitoring of vital signs and electrolytes.[31]