Should You Order a PCN for Asymptomatic Hydronephrosis After Urinary Diversion?

A 68-year-old male with a remote history of radical cystectomy and ileal conduit creation for bladder cancer presents for routine follow-up. He feels well, with normal urine output from his stoma and no flank pain. A surveillance CT, however, reveals new moderate bilateral hydronephrosis. His white blood cell count is normal, he is afebrile, and a recent loopogram showed no reflux into the ureters, leaving the cause of the obstruction unclear. You are now faced with a critical decision: how to manage this silent, but significant, new finding to preserve his renal function.

This scenario requires a careful, stepwise approach to both diagnose the etiology of the obstruction and provide therapeutic decompression. According to the American College of Radiology (ACR) Appropriateness Criteria, the next step in management is Percutaneous Nephrostomy (PCN), which includes the potential for a Percutaneous Nephroureterogram (PCNU). This intervention is rated as Usually appropriate.

Who Fits This Clinical Scenario?

This guidance applies to a very specific patient population: individuals with a remote history of cystectomy and urinary diversion (such as an ileal or colonic conduit) who present with new, incidentally discovered hydronephrosis. The key inclusion criteria for this workflow are:

• A history of urinary diversion (e.g., ileal conduit).
• New moderate or severe hydronephrosis on a cross-sectional imaging study like CT or MRI.
• An absence of clinical signs of infection, such as fever or leukocytosis.
• Normal or stable urine output from the stoma.
• A recent loopogram (an imaging study of the conduit) that fails to demonstrate reflux into the ureters, meaning it does not visualize the site of obstruction.

It is crucial to distinguish this clinical picture from similar but distinct scenarios that require different management pathways. This article does not apply if the patient presents with signs of infection. For instance, a patient with a seven-day history of flank pain, fever, and leukocytosis has a presumed pyonephrosis, which represents a urologic emergency. Similarly, this guidance is not tailored for pregnant patients with obstructive uropathy or patients with known advanced malignancy causing renal failure, as each of those situations has its own dedicated ACR workflow.

What Diagnoses Are You Working Up in This Scenario?

In a patient with a urinary diversion and new, silent hydronephrosis, the differential diagnosis centers on the potential causes of obstruction at the ureteroenteric anastomosis or within the retroperitoneum. The goal of the workup is to differentiate between benign and malignant causes while protecting renal function.

Benign Ureteroenteric Anastomotic Stricture: This is the most common cause of late-onset obstruction following urinary diversion. These strictures are typically fibrotic and may result from ischemia, inflammation, or scarring related to the original surgery. They develop gradually, which explains the patient’s lack of acute symptoms despite significant hydronephrosis.

Malignant Recurrence: A less common but critical diagnosis to exclude is recurrent malignancy. The original cancer (e.g., urothelial carcinoma) can recur at the anastomosis or as nodal disease in the retroperitoneum, causing extrinsic compression of the ureters. This is a primary concern in any patient with a history of cancer presenting with new obstruction.

Ureteral Stone Disease: Patients with urinary diversions can have metabolic changes that predispose them to stone formation. While less common than strictures, a stone lodged at the anastomosis or within the ureter could cause obstruction. The non-contrast portion of the CT scan should be carefully reviewed for this possibility.

Retroperitoneal Fibrosis: This is a rare condition characterized by the proliferation of fibrous tissue in the retroperitoneum, which can encase and obstruct the ureters. It can be idiopathic or secondary to prior surgery, radiation, or certain medications. While uncommon, it remains a possibility in this clinical context.

Why Is PCN (includes PCNU) the Recommended Study for This Presentation?

The ACR designates Percutaneous Nephrostomy (PCN), often followed by a diagnostic antegrade study (PCNU), as Usually appropriate because it uniquely serves as both a diagnostic and a therapeutic intervention in this specific scenario. It directly addresses the primary risk—silent loss of renal function—while providing the access needed to define the underlying pathology.

The primary rationale for PCN is to establish immediate and reliable drainage of the obstructed upper urinary tracts. This decompression is crucial for preserving renal parenchyma, even when serum creatinine is still within the normal range. Once the PCN tube is in place, it provides a direct antegrade route to the site of obstruction. An antegrade nephroureterogram (PCNU) can then be performed by injecting contrast through the tube. This study will almost always delineate the exact location, length, and morphology of the obstruction, providing the diagnostic information that the non-refluxing loopogram could not.

Let’s consider the alternatives and why they are rated lower for this patient:

• Retrograde ureteral stenting is rated as May be appropriate. While less invasive in theory, it is often technically challenging or impossible in patients with urinary diversions. Identifying and cannulating the small ureteral orifices within the bowel mucosa of the conduit can be difficult, especially in the presence of a tight stricture. The fact that the loopogram showed no reflux already suggests that retrograde access will be problematic. Attempting and failing a retrograde approach only delays necessary decompression.
• Medical management without decompression is rated Usually not appropriate. This is a critical point. The absence of symptoms like pain or fever does not negate the danger posed by the obstruction. Progressive, silent hydronephrosis leads to irreversible nephron loss and chronic kidney disease. Electing to simply monitor the patient would be to accept a high risk of permanent renal damage.

The PCN procedure is performed under imaging guidance (ultrasound and/or fluoroscopy) and involves radiation. The dose is variable but generally low. Iodinated contrast is used for the diagnostic PCNU portion, so the patient’s renal function and contrast allergy history should be considered. The immediate benefit of preserving kidney function typically far outweighs the risks of the procedure.

What’s Next After PCN (includes PCNU)? Downstream Workflow

Placement of a percutaneous nephrostomy tube is the first step, not the final treatment. The findings from the subsequent antegrade nephroureterogram will guide the downstream management plan.

If the study reveals a benign-appearing stricture: The interventional radiologist can often treat the stricture percutaneously. This may involve balloon dilation of the stricture followed by the placement of an internal-external nephroureteral stent (which traverses the stricture and drains into the conduit) or a temporary internal ureteral stent. This approach can sometimes provide a durable solution or serve as a bridge to a definitive surgical revision of the ureteroenteric anastomosis.

If the study suggests malignant obstruction: An antegrade approach allows for direct access for tissue sampling. A brush biopsy or a direct percutaneous biopsy of any associated soft tissue mass can be performed to confirm the diagnosis of recurrent cancer. The PCN tube provides reliable, long-term drainage while the patient is referred back to oncology for systemic therapy or radiation.

If the study is indeterminate or shows no clear obstruction: In rare cases, the ureters may be dilated without a fixed mechanical obstruction (an “atonic” system). If there is clinical suspicion for a functional rather than mechanical blockage, a Whitaker test can be performed through the PCN tube. This urodynamic study measures pressure in the renal pelvis during fluid infusion to determine if a physiologically significant obstruction exists.

Pitfalls to Avoid (and When to Get Help)

Navigating this clinical scenario requires avoiding several common pitfalls that can lead to delayed diagnosis and adverse outcomes.

1. Equating “Asymptomatic” with “Benign”: The most significant pitfall is being falsely reassured by the patient’s lack of symptoms. Silent hydronephrosis is insidious and can cause irreversible renal damage if left untreated. The imaging finding of new, moderate hydronephrosis is the key action signal.
2. Delaying Decompression: Do not wait for the serum creatinine to rise before acting. Creatinine is an insensitive marker of early renal injury, especially in cases of unilateral or incomplete bilateral obstruction. The goal is to intervene before significant functional loss occurs.
3. Over-reliance on Retrograde Approaches: While a retrograde attempt by urology may seem less invasive, it has a lower probability of success in this specific context (post-cystectomy with a non-refluxing loopogram). Persisting with failed retrograde attempts delays the definitive decompression provided by a PCN.

If the patient develops any signs of infection (fever, chills, leukocytosis) or a rapid decline in renal function, the situation becomes a urologic emergency. In such cases, you should escalate immediately for urgent percutaneous drainage.

Related ACR Topics and Tools

For a comprehensive overview of managing various forms of urinary tract obstruction, this depth piece is best used alongside our broader guide. Additionally, several tools can help you apply these principles in your daily practice.

• For breadth across all scenarios in Radiologic Management of Urinary Tract Obstruction, see our parent guide: Radiologic Management of Urinary Tract Obstruction: ACR Appropriateness Decoded.
• To explore adjacent clinical scenarios and see how imaging recommendations change, use the Imaging Appropriateness Selector.
• For details on how specific procedures are performed, consult the Imaging Protocol Library.
• To discuss cumulative radiation exposure with your patients, the Radiation Dose Calculator can be a helpful resource.

Frequently Asked Questions

Why not go straight to surgery if a benign stricture is the most likely cause?

While surgery is the definitive treatment for a benign stricture, proceeding directly to a major revision surgery on an obstructed, decompensated kidney carries higher risk. Placing a PCN tube first decompresses the system, allows renal function to recover, reduces inflammation, and provides a precise roadmap of the anatomy via a nephroureterogram. This makes the subsequent surgery safer and more likely to succeed. In some cases, percutaneous balloon dilation and stenting can even defer or eliminate the need for surgery.

What is the difference between a PCN and a PCNU?

PCN stands for Percutaneous Nephrostomy, which is the procedure of placing a drainage tube (catheter) through the skin directly into the kidney’s collecting system. PCNU stands for Percutaneous Nephroureterogram, which is the diagnostic imaging study performed through that tube. After placing the PCN, contrast is injected to opacify the entire upper urinary tract (renal pelvis, ureter) down to the point of blockage. The PCN is the therapeutic access; the PCNU is the diagnostic study performed through it.

The patient’s creatinine is normal. Why is decompression still necessary?

Serum creatinine is an insensitive marker for kidney damage, especially with chronic or partial obstruction. A significant amount of renal function (up to 50%) can be lost before creatinine levels rise above the normal range. In this patient with bilateral hydronephrosis, waiting for the creatinine to become abnormal means that substantial, potentially irreversible damage has already occurred. The goal of intervention is to prevent that damage.

Can’t we just try a retrograde approach first since it might be less invasive?

A retrograde approach, performed by a urologist, involves passing a scope into the urinary conduit to find and stent the ureters from below. While it avoids a skin puncture, it is often unsuccessful in this specific scenario. The ureteral orifices can be difficult to find within the bowel conduit, and a tight stricture may be impossible to cross from below. The fact that a loopogram showed no reflux already predicts this difficulty. An unsuccessful retrograde attempt delays necessary treatment, which is why the ACR recommends a PCN as the more reliable primary approach.

How long will the nephrostomy tube need to stay in?

The duration depends entirely on the underlying cause and the definitive treatment plan. If the obstruction is due to a benign stricture that is treated with balloon dilation and an internal stent, the external PCN tube may be removed within days or weeks. If the cause is a malignant obstruction requiring chemotherapy, the tube may need to remain in place for months to provide durable drainage. The PCN tube serves as a bridge to the next step in management.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 26, 2026