Is perinephric stranding on computed tomography (CT) common in patients with urostomy?

Perinephric Stranding in Urostomy Patients

Perinephric stranding on CT is not a typical or expected finding in patients with urostomy alone and should prompt evaluation for underlying pathology such as infection, obstruction, or ureteral injury.

Understanding Perinephric Stranding

Perinephric fat stranding (PFS) represents inflammatory changes in the fat surrounding the kidney and is a secondary CT finding that indicates an active pathologic process rather than a normal anatomical variant 1.

Clinical Significance of PFS

PFS is a marker of significant renal or ureteral pathology and predicts:

• Bacteremia in acute pyelonephritis - PFS presence increases bacteremia risk from 23.1% to 55.2% 2
• Febrile urinary tract infection - PFS is an independent predictor of post-procedural UTI 3
• Ureteral obstruction - PFS has an odds ratio of 6.15 for predicting any degree of obstruction 4
• Ureteral injury - PFS is a key finding suggesting ureteral trauma, particularly in blunt trauma 1, 5

PFS in Urostomy Context

When PFS Should Raise Concern

In patients with urostomy (urinary diversion after cystectomy), PFS is not normal and indicates:

1. Ureteroileal stricture with obstruction - The most common cause in urostomy patients, where anastomotic strictures develop and cause upstream obstruction 1

2. Pyonephrosis/infected obstruction - PFS combined with hydronephrosis suggests infected obstructed kidney requiring emergent decompression 1

3. Ureteral leak or injury - PFS with perirenal fluid suggests anastomotic breakdown or ureteral injury 1, 5

4. Bladder outlet obstruction equivalent - In ileal conduit patients, mucus plugging or conduit obstruction can cause bilateral PFS similar to bladder outlet obstruction 6

Diagnostic Algorithm When PFS is Present

If PFS is identified on CT in a urostomy patient, the following evaluation is mandatory:

• Check for fever, leukocytosis, and sepsis signs - PFS with systemic infection requires emergent percutaneous nephrostomy 1
• Assess for hydronephrosis/hydroureter - PFS combined with collecting system dilation confirms obstruction 1, 4
• Perform loopogram - Evaluate for reflux into ureters and identify stricture location 1
• Obtain blood cultures if febrile - PFS predicts bacteremia even with prior antibiotics 2

Management Based on Findings

For PFS with pyonephrosis (infected obstruction):

• Emergent percutaneous nephrostomy is lifesaving and usually appropriate 1
• Preprocedural antibiotics are mandatory 1
• Patient survival is 92% with PCN versus 60% with medical therapy alone 1

For PFS with non-infected obstruction:

• Percutaneous nephrostomy followed by delayed surgical revision is usually appropriate 1
• Antegrade nephroureteral catheter placement is preferred over double-J stents due to mucus plugging risk 1

For PFS with suspected ureteral leak:

• Delayed excretory phase CT confirms extravasation 1, 5
• Percutaneous nephrostomy provides decompression and allows healing 1

Critical Pitfalls to Avoid

• Do not assume PFS is "normal" in urostomy patients - It always indicates active pathology requiring investigation 1
• Do not delay drainage if infection is present - PFS with fever/sepsis requires emergent decompression within hours 1
• Do not rely on hematuria - Up to 25% of ureteral injuries lack hematuria despite PFS 1
• Do not use double-J stents as first-line in ileal conduits - They occlude rapidly from mucus; retrograde nephroureteral catheters are preferred 1

Interobserver Reliability Consideration

PFS interpretation has moderate interobserver variability (kappa 0.26-0.60), so bilateral PFS or severe PFS is more reliable than subtle unilateral findings 4. When PFS is bilateral (which occurs in 80-93% of cases), the finding is more clinically significant 6.