Obstructive Uropathy: Presentation, Evaluation, and Management

Author: Andrew Kuschnerait, MD (Emergency physician, San Antonio, TX) // Reviewed by: Andy Grock, MD; Alex Koyfman, MD (@EMHighAK); Brit Long, MD (@long_brit)

Case 1

A 76-year-old male presents with suprapubic pain, fever and dysuria for the past two days. The patient has a history of BPH and has been out of his finasteride for several months. Today, he reports several weeks of progressively weaker stream, inability to completely void, and frequent bouts of small volume incontinence, especially with sneezing and coughing. Vitals are: Temp 101 F (38.3 C), HR 116, BP 170/90, RR 18, Sat 99% on RA. Physical exam is remarkable for suprapubic and bilateral lower quadrant tenderness as well as lower abdominal fullness. Bedside US demonstrates a normal aorta; but a distended bladder, large prostate and bilateral hydronephrosis. Labs are significant for a White Blood Cell (WBC) count of 18 x 10⁹ /L with a left shift, and serum creatinine  of 2.4 mg/dL (baseline 1.2 mg/dL). UA shows too numerous WBCs to count, with positive leukocyte esterase (LE) and Nitrite.

Case 2

A 34-year-old male with no medical history presents with sudden onset left flank pain radiating to the left groin for the past 10 hours. The patient states the pain comes on in waves. He endorses nausea without vomiting and is able to drink fluids well. The patient denies fever, dysuria, frequency or urgency. Vital signs are: Temp 98.6 F (37 C), HR 96, BP 142/80, RR 16, Sat 100% on RA. On exam, the patient appears very uncomfortable. The abdomen is soft, nontender and nondistended. Back exam is normal without costovertebral-angle tenderness. Genitourinary examination is also benign. Bedside US reveals left kidney moderate hydronephrosis and absence of left ureteral jets in the bladder. The urinalysis shows red blood cells (RBCs) without WBC, LE ,or Nitrite, and the rest of the labs including renal function are within normal limits.

Background

Obstructive uropathy refers to any interference of urinary flow from its start at filtration from blood plasma in the kidneys to expulsion from the urethra. It can be caused by many pathologic conditions ranging from intrinsic (stones, infection, blood clots, papillary/renal tubule necrosis, renal cell carcinoma, transitional cell carcinoma) or extrinsic (tumors, AAA, pregnancy, BPH/prostatitis, phimosis, neurogenic bladder) pathologic conditions. The incidence of various obstructive uropathy etiologies is largely unstudied, but the most common appear to be kidney stones at 1.3 million ED visits/year¹ and prostate enlargement, at a rate of  50% of males over the age of 60².  Many etiologies are more prevalent with older age such as tumors, prostate enlargement, neurogenic bladders, pelvic floor weakness and various diseases of the kidney.

Categorizing obstructive uropathy as painful/painless, unilateral/bilateral, complete/partial, or acute/chronic, does not aid in the diagnosis due to the overlap in presentations. For example, obstruction duration affects pain severity, location can result in either unilateral or bilateral hydronephrosis, and lastly, the amount obstructed can affect the amount of urinary flow. Generally, obstructive uropathy should be viewed as a symptom of another disease, instead of a final diagnosis.

The most relevant signs and symptoms in obstructive uropathy are:

• Pain – Most commonly abdominal and/or flank pain, though can be absent
• Hematuria – gross or microscopic
• Urinary symptoms -slowed stream, incomplete bladder emptying, decreased urine output
• Increased Creatinine – especially when bilateral or unilateral with underlying kidney disease
• Hypertension – secondary to reduced filtration and reflex renal artery constriction

Importantly, obstructive uropathy with acute kidney injury and/or infection, such as urinary tract infection (UTI) or pyelonephritis, must be reversed/decompressed emergently. On the other hand, unilateral obstructive uropathy without AKI/infection does not require emergent therapy. Unilateral obstructions are unlikely to reduce glomerular filtration rate due to compensation from the unaffected kidney if it is healthy. Animal studies demonstrated high rates of renal recovery with obstructions lasting less than two weeks in comparison, recovery was around 31% at 28 days and 8% with obstructions lasting 60 days. ⁴ In these prolonged cases, the obstruction causes vascular contraction of the affected kidney which is worsened by release of angiotensin and thromboxanes. Eventually this process leads to irreversible damage from ischemia and inflammation for which the remaining healthy nephrons cannot compensate.  Fortunately, most cases of obstructive uropathy are reversible.

Differential

The differential for obstructive uropathy includes:

Intrinsic: Direct blockage to the flow of urine

• Stones: Very common, an intrinsic cause of obstructive uropathy, and can obstruct any level of the urogenital tree.
  • Consider extrinsic causes that lead to increased stone formation such as increased oxalate absorption from inflammatory bowel disease.
• Posterior urethral valve: Most common cause of urinary obstruction in newborn males
  • Most common cause of chronic renal disease due to obstruction in children
• Meatal Stenosis: Usually a complication of circumcision/inflammation in men
• Urethral Caruncle: Benign, most common lesion of female urethra (post-menopausal)
• Cancer (intrinsic)
  • Renal Cell Carcinoma: 80-85% of all primary renal neoplasms.⁶
  • Urothelial (formerly called transitional cell) carcinoma accounts for 90% of bladder cancers but can also occur in the renal pelvis or ureter. Bladder cancer is the 9^th most common cancer in the world.⁷
  • Nephroblastoma / Wilms Tumor: 5-6% of all primary renal neoplasm.
  • Oncocytomas, collecting duct tumors, renal sarcomas: Rare

Extrinsic: Compression of structures responsible for flow of urine

• Retrocaval ureter: Ureter passes underneath inferior vena-cava
• Ovarian artery syndrome: Ovarian vein passes over and compresses ureter
• Benign prostate hyperplasia: Extremely common
• Cancers (Extrinsic)
• Ovarian Cancer: Second most common gynecologic cancer, lifetime risk 1.3%
• Prostate Cancer: Most common cancer in men, 1.6 Million cases/year
• Retroperitoneal metastasis: Most likely from prostate, breast or testicle.
• Colon Cancer

Other causes include: other cancerous and anatomical causes, infections such as schistosomiasis, prostatitis, tubo-ovarian abscess, blood clots, pregnancy, various strictures, diverticulum (I.E bladder), trauma, various diseases leading to neurogenic bladder and adverse drug reactions. Again, the most common will be either stone formation and prostate enlargement.

Evaluation

Obstructive uropathy may require labs (including a creatinine), imaging, either ultrasound or computed tomography (CT), or urinalysis based on the presentation.

Point of care ultrasound (POCUS) is a rapid, reliable, and inexpensive modality to evaluate for obstructive uropathy. POCUS can more rapidly confirm obstructive uropathy complications, though it may not negate the need for a CT scan. In experienced hands, ultrasound has up to a 98% sensitivity for obstruction. However, mild hydronephrosis, renal pelvic dilation with some caliceal dilation with no medulla or cortex changes, can be seen without obstruction at all. Hence, it carries a 26% false positive rate for obstruction³. Moderate (renal pelvic and caliceal dilation with thinning of the medulla) and severe hydronephrosis (moderate plus thinning of medulla and cortex) carry higher positive predictive values.

Case 1: Evaluation

Case 1 above describes an elderly gentleman with a clinical picture suggesting urinary infection and obstruction, which would require emergent therapy once the etiology is discovered. Imaging is indicated either with CT scan of the abdomen and pelvis or a more rapidly obtained bedside ultrasound. Given his age and tenderness, he would likely benefit from a CT. His ultrasound images are shown in image 2 and 3 below.

Image 2 (case 1) demonstrates mild-moderate or grade 2 hydronephrosis via ultrasound, which indicates that the obstruction is distal in the urinary system. If it is bilateral, this suggests the obstruction is between the bladder and urethral meatus. Pregnancy and a large mass may also result in bilateral hydronephrosis.

Bladder ultrasound after micturition reveals an enlarged prostate and retained urine. These images support prostate enlargement and obstruction as the etiology for this patient’s urinary obstruction.

Case 1’s bilateral hydronephrosis combined with a UTI indicate he requires emergent decompression. A CT scan may still be indicated to evaluate for other intra-abdominal etiologies given his history, risk factors, and physical exam. However, targeted treatment and specialty consultation can be initiated at this time.

Case 2: Evaluation

In case 2, our patient presents with classic renal colic. His POCUS (Image 4) shows unilateral hydronephrosis and an absence of ipsilateral ureterovesicular (UVJ) jets, which is highly suggestive of a complete, unilateral obstruction.

Radiologist performed US has a sensitivity and specificity for obstruction as high as 98.3% and 100%, respectively. Emergency physician performed US sensitivity and specificity is lower at 70-85% and 50-92%, respectively¹. In the right clinical scenarios (young, healthy, history of stones, typical symptoms), ultrasound alone can clinch the diagnosis. POCUS does not show hydronephrosis in approximately 11% of patients with ureterolithiasis.⁵ Hence, a patient with clinical renal colic and no hydronephrosis may require a CT scan. CT without contrast can specifically identify the stone size and location and may be indicated, especially in older patients suspected of having another high-risk disease. A urinalysis may help diagnose a UTI. Other laboratory tests may be indicated as clinically warranted.

In fact, one large study randomly assigned suspected renal colic patients to ED POCUS, radiology POCUS, or CT first. The US first group had no increased risk of adverse events and received less frequent CTs¹⁰.

If UVJ jets are present on US, it makes renal colic less likely. On the other hand, an absent jet in someone with typical symptoms makes renal colic very likely. Additionally, if hydronephrosis is present, the stone has an increased risk of being >5mm which portends to a <20% chance of passing on its own¹. Thus, the otherwise well appearing, PO tolerant and healthy patient can be discharged with an outpatient urology consultation rather than uniformly obtaining a CT scan.

Of note, obstructive uropathy rarely causes significant acute kidney injury in adults. However, it is more commonly found in children with acute kidney injury and/or UTI due to congenital malformations (posterior urethral valves for example )³. This association is likely due to delay in diagnosis, prolonged obstruction, bilateral obstruction, or a combination of these features.

In summary, for obstructive uropathy POCUS is a safe, fast and less expensive initial imaging modality.   Obstructive uropathy patients should be evaluated for a UTI and possibly an acute kidney injury per the creatinine/GFR, especially if the obstruction is bilateral on imaging. If any of these are present emergent decompression of the obstruction is needed; if not, continued investigation as to the etiology is indicated.

Management

Obstructive uropathy management depends on the etiology with emergent therapy for bilateral obstruction, an acute kidney injury, or urinary tract infection. For obstructions distal to the bladder, such as BPH, placing a foley catheter is appropriate. Coude catheters are angulated at the tip and make passage through the urethral bend in an enlarged prostate easier.

In distal obstructions for which a foley catheter cannot pass, a suprapubic catheter may be needed. This is placed percutaneously and is a relatively simple procedure to perform. The image below depicts its general placement. If it’s emergently indicated and specialty consultation is not available, emergency physicians should place the suprapubic catheter.

More proximal obstructions and obstructions that cannot be bypassed by these two modalities usually require ureteral stenting or nephrostomy drainage. Image 8 below  depicts nephrostomy tube placement, which is placed through the skin and kidney targeting the renal pelvis. Image 9 depicts a ureteral stent in place (arrows are not relevant for this purpose). Straightening of one of the two coiled ends indicates displacement of the stent through the ureter.

Both stenting and nephrostomy tubes have evidence supporting their effectiveness in ureteral calculi with obstruction and infection^8,9. In ureteral stenting, a hollow bore tube is placed in the ureter, which allows for both urine drainage and dilation to improve debris passage. It is less invasive than a percutaneous nephrostomy tube with less risk of bleeding from tube insertion through the skin, kidney parenchyma and into the renal pelvis. However, nephrostomy tubes may be preferred if ureteral stents are not be available or further stone management with percutaneous methods are needed (>2cm stones in kidney and cysteine stones resistant to lithotripsy).

In case 1 the patient requires infection/sepsis management as well as bladder decompression with foley or suprapubic catheter placed. Definitive management may involve surgery to remove the prostate or pharmacological, depending on patient preference and biopsy evaluation. In case 2 emergent drainage is not indicated. Depending on stone size the patient may require ureteral stenting vs lithotripsy. Case 1 would require emergent urology consult, while case 2 can follow-up with them as an outpatient.

Summary

• Obstructive uropathy is a complication of many conditions.
• POCUS is crucial in decreasing time to diagnosis and definitive management.
• AKI, infection in the urinary tree, and bilateral obstructions need drainage as soon as possible.

References/Further Reading:

1) Tyczynska N, Feng CH. Urolithiasis. Emergency Medicine Reviews and Perspectives CorePendium.  2020 October.

2) Berry S.J., Coffey D.S., Walsh P.C., Ewing L.L. The development of human benign prostatic hyperplasia with age. J Urol. 1984;132:474–479.

3) Zeidel ML, O’Neil C. Clinical manifestations and diagnosis of urinary tract obstruction and Hydronephrosis. UpToDate May 2019.

4) Singh I, Strandhoy JW, Assimos, DG. Pathophysiology of Urinary Tract Obstruction. Campbell – Walsh Urology. 10th ed. 2012: 1090-1092.

5) Song Y, Hernandez N, et al. Can ureteral stones cause pain without causing hydronephrosis? World J Urol. 2016 Sep;34(9):1285-8.

6) Atkins MB. Clinical manifestations, evaluation, and staging of renal cell carcinoma. UpToDate.

7) Lerner PL, Raghavan D. Overview of the initial approach and management of urothelial bladder cancer. UpToDate.

8) Pearle MS, Pierce HL, et al. Optimal method of urgent decompression of the collecting system for obstruction and infection due to ureteral calculi. Journal of Urology 1998; 160(4):1260.

9) Ramsey S, Robertson A. Evidence-based drainage of infected hydronephrosis secondary to ureteric Calculi. J Endourol. 2010;24(2):185.

10) Smith-Bindman R, Aubin C, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med. 2014 Sep 18;371(12):1100-10.