Interventional Radiology Imaging

How Should You Manage an Infected Ureteral Stone Without Hydronephrosis on CT?

·
How Should You Manage an Infected Ureteral Stone Without Hydronephrosis on CT?

It’s late in the day when you review the CT scan of a patient with a seven-day history of worsening right flank pain, fever, and leukocytosis. The urinalysis confirms infection. The CT report is clear: there is a 10 mm calculus in the mid-right ureter, but surprisingly, no significant hydronephrosis. This clinical picture—an infected system with a known obstruction—represents a urologic emergency, yet the absence of collecting system dilation can be a misleading finding. The critical decision is not if to intervene, but how to decompress the system urgently. This article details the American College of Radiology (ACR) Appropriateness Criteria workflow for this specific, high-risk scenario. For this presentation, the ACR panel on Interventional Radiology finds that Retrograde ureteral stenting is Usually appropriate.

Who Fits This Clinical Scenario?

This guidance applies to a specific and urgent clinical presentation: a patient with clear evidence of both urinary tract infection and obstruction. The key inclusion criteria are:

  • Systemic Signs of Infection: The patient presents with fever and an elevated white blood cell (WBC) count.
  • Localizing Symptoms: Flank pain points to a renal or ureteral cause.
  • Urinalysis Findings: Evidence of infection (pyuria, bacteriuria) and often hematuria.
  • Confirmed Obstruction: A prior imaging study, typically a non-contrast CT scan, has identified an obstructing calculus (in this case, a 10 mm stone in the mid ureter).
  • Absence of Hydronephrosis: This is the crucial, and potentially confusing, feature of this scenario. Despite the obstruction and infection, the collecting system is not significantly dilated.

This workflow is distinct from other scenarios. It does not apply to patients who are hemodynamically unstable or septic, as they may require more aggressive resuscitation and potentially different management priorities. It also differs from the workup of a pregnant patient with similar symptoms, where imaging and intervention choices are constrained by fetal safety. Finally, this is not the pathway for obstruction due to malignancy, such as advanced cervical cancer, which involves different long-term considerations.

What Diagnoses Are You Working Up in This Scenario?

The primary and most urgent diagnosis to address is an infected, obstructed upper urinary tract. This condition is a urologic emergency because the combination of infection and obstruction creates a closed-space infection. Pus under pressure within the renal collecting system (pyonephrosis) can lead to rapid clinical deterioration, urosepsis, and irreversible kidney damage. The absence of hydronephrosis does not rule out a functionally significant obstruction. The ureter may be completely blocked, but if the condition is acute or if there has been a small forniceal rupture decompressing the system into the retroperitoneum, significant dilation may not have had time to develop.

A secondary consideration is obstructive pyelonephritis. While pyelonephritis is an infection of the kidney parenchyma, the presence of a downstream stone severely complicates treatment. Antibiotics alone are often insufficient because they cannot achieve adequate concentrations in the obstructed, poorly perfused renal tissue upstream of the calculus. The infection will not clear until the obstruction is relieved and urinary drainage is restored.

Less likely, but still a consideration, is a perinephric abscess. An untreated or undertreated pyonephrosis can rupture, leading to a collection of pus around the kidney. While the initial CT did not show this, it is a potential sequela if decompression is delayed. The clinical focus remains on the primary problem: relieving the obstruction to treat the infection.

Why Is Retrograde Ureteral Stenting the Recommended Intervention?

For an infected and obstructed ureter caused by a calculus, the immediate goal is decompression. The ACR rates Retrograde ureteral stenting as Usually appropriate because it directly and effectively addresses this need. This procedure is typically performed by a urologist using cystoscopy to access the bladder and ureteral orifice. A guidewire is passed up the ureter beyond the stone, and a flexible plastic tube (stent) is placed over the wire, with one end in the renal pelvis and the other in the bladder. This bypasses the obstruction, re-establishes urine flow, and allows the infection to drain.

This approach is favored because it is minimally invasive, avoids an external drainage tube, and can often be performed quickly. It provides immediate internal drainage, which is critical for controlling the infection and allowing systemic antibiotics to become effective.

Alternative interventions received lower ratings for this specific scenario:

  • PCN (Percutaneous Nephrostomy): Rated as May be appropriate. This procedure, performed by an interventional radiologist, involves placing a drainage tube directly into the renal collecting system through the skin of the flank. It is an excellent method for decompression and is a crucial alternative if retrograde stenting fails or is not feasible. However, it is often considered second-line because it is more invasive and leaves the patient with an external tube and drainage bag, which can impact quality of life and requires care.
  • Medical management without decompression: Rated as Usually not appropriate. This is the most significant pitfall to avoid. Attempting to treat an infected, obstructed system with antibiotics alone is dangerous. Without drainage, the infection is unlikely to resolve and the risk of sepsis is high. This is a surgical/procedural problem, not a purely medical one.

The choice between retrograde stenting and PCN often comes down to institutional resources, specialist availability, and specific patient factors. However, for a stable patient, the initial attempt is typically a retrograde stent.

What’s Next After Retrograde Ureteral Stenting? Downstream Workflow

The management pathway continues immediately after the decompression procedure. The patient’s clinical response is the most important guide for next steps.

If the procedure is successful and the patient improves: Following successful stent placement, the patient should be admitted for continued intravenous antibiotics and observation. You should see a rapid improvement in fever, leukocytosis, and flank pain within 24-48 hours. Once the infection is controlled and the patient is clinically stable, they can be discharged. The ureteral stent remains in place. The patient will then need to follow up with urology as an outpatient for definitive management of the 10 mm calculus, which could involve procedures like shock wave lithotripsy (SWL) or ureteroscopy with laser lithotripsy. The stent is typically removed after the stone has been treated.

If retrograde stenting is unsuccessful: In some cases, the urologist may be unable to bypass the stone with a guidewire. If this occurs, the patient requires immediate alternative decompression. The next step is an urgent consultation with interventional radiology for a percutaneous nephrostomy (PCN) tube placement. This ensures the system is drained promptly.

If the patient fails to improve after stenting: If fever and leukocytosis persist despite a successfully placed stent and appropriate antibiotics, you must consider complications. The stent could be malpositioned or occluded, or the patient may have developed a perinephric abscess that also requires drainage. In this situation, repeat cross-sectional imaging, typically with a contrast-enhanced CT, is warranted to reassess the anatomy and look for a drainable fluid collection.

Pitfalls to Avoid (and When to Get Help)

In this high-stakes scenario, several common pitfalls can lead to poor outcomes. The most critical is being falsely reassured by the lack of hydronephrosis on the initial CT scan. An infected, obstructed kidney is an emergency regardless of the degree of dilation. Do not delay intervention.

A second pitfall is attempting to manage the patient with antibiotics alone. While essential, antibiotics are adjunctive to the primary treatment, which is mechanical decompression of the urinary tract. Delaying a call to urology or interventional radiology to “see if the antibiotics work” is a dangerous course of action.

Finally, always assess the patient’s coagulation status and ability to lie prone or supine for a procedure before consulting for intervention. Correcting any coagulopathy is a necessary prerequisite for either a retrograde stent or a percutaneous nephrostomy. If the patient’s clinical status deteriorates rapidly, showing signs of sepsis or hemodynamic instability, escalate immediately to the intensive care unit for resuscitation in parallel with the urgent urologic or interventional radiology consultation.

Related ACR Topics and Tools

This article covers one specific variant in a broader topic. Clinicians should be familiar with the full range of presentations and the tools available to ensure appropriate care. 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.

For additional decision support and technical details, the following GigHz resources are available:

Frequently Asked Questions

Why is this situation an emergency if there is no hydronephrosis on the CT scan?

The absence of hydronephrosis does not rule out a high-pressure, obstructed system. In an acute obstruction, the collecting system may not have had time to dilate. Furthermore, the infection itself causes inflammation and swelling that increases pressure. An infected, obstructed urinary tract is a closed-space infection, which is a urologic emergency that can rapidly progress to sepsis, regardless of the degree of dilation seen on imaging.

What is the difference between retrograde and antegrade ureteral stenting?

Retrograde stenting is performed from below, via the bladder and ureteral orifice, typically by a urologist. Antegrade stenting is performed from above, through a percutaneous access tract into the kidney, typically by an interventional radiologist. For this scenario, retrograde stenting is the primary recommendation. Antegrade stenting is rated ‘Usually not appropriate’ as a primary intervention, though it may be performed after a percutaneous nephrostomy tract is already established.

In this specific patient, when would a percutaneous nephrostomy (PCN) be chosen over a retrograde stent?

A PCN tube would be the preferred initial choice if retrograde stenting is technically impossible (e.g., the urologist cannot get a wire past the stone), if there is complex anatomy that prevents a retrograde approach, or if the patient is too unstable for the anesthesia required for cystoscopy. It is also the primary rescue procedure if a retrograde stent fails.

How long will the ureteral stent need to stay in place?

The stent is a temporary measure to drain the infection. It will remain in place until the infection has completely resolved and the patient is stable enough for a definitive procedure to remove the 10 mm stone. This is typically done on an outpatient basis several weeks later. The stent is usually removed at the same time as, or shortly after, the definitive stone treatment.

Can this patient be managed with just IV antibiotics and observation?

No. According to the ACR Appropriateness Criteria, medical management without decompression is ‘Usually not appropriate.’ Antibiotics cannot effectively penetrate a pressurized, obstructed system to clear the infection. Relieving the obstruction via a stent or nephrostomy tube is essential to prevent sepsis and preserve kidney function. This is a procedural emergency.

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