What does perinephric stranding on a computed tomography (CT) scan indicate?

From the Guidelines

Perinephric stranding on a computed tomography (CT) scan is indicative of inflammation or edema in the perinephric fat, which surrounds the kidneys.

Key Associations

• This finding is often associated with pyelonephritis or other infectious processes, and may also be seen in the context of renal trauma, obstruction, or vasculitis 1.
• The presence of perinephric stranding may be less apparent on low-dose CT than on standard-dose CT 1.

Clinical Implications

• In clinical practice, the presence of perinephric stranding may prompt further evaluation, including:
  • Urine culture and sensitivity testing
  • Potentially the initiation of antibiotic therapy, such as ciprofloxacin 500mg orally twice daily for 7-14 days, depending on the underlying cause and severity of the condition.
• A contrast-enhanced CT can be used to detect signs of acute pyelonephritis, including focal or multifocal decreased parenchymal enhancement, complications of pyelonephritis, and underlying problems such as hydronephrosis or obstructing stones 1.
• The use of CT abdomen and pelvis without IV contrast may be useful in evaluating symptomatic patients with hydronephrosis of unknown cause, particularly when obstructive urolithiasis is a primary concern 1.

From the Research

Perinephric Stranding on CT Scan

Perinephric stranding on a computed tomography (CT) scan is a clinical finding that can indicate various conditions. The following are some possible indications of perinephric stranding:

• Infection or inflammation of the kidney, such as acute pyelonephritis 2, 3, 4
• Bladder outlet obstruction (BOO) 5
• Surgical difficulties in simple nephrectomy due to inflammation or adherent perinephric fat 6
• Bacteraemia, with a higher rate of bacteraemia found in patients with perinephric fat stranding (PFS) 3

Diagnostic Value of Perinephric Stranding

The diagnostic value of perinephric stranding is still unclear, with some studies suggesting that it is not a powerful diagnostic tool for acute pyelonephritis 4. However, other studies have found that PFS can be a useful sign to alert clinicians to consider acute pyelonephritis or BOO 2, 3, 5.

• Sensitivity and specificity of PFS for diagnosing acute pyelonephritis: 72% and 58%, respectively 4
• Positive likelihood ratio of PFS for diagnosing acute pyelonephritis: 1.7 4
• Association between PFS severity and urodynamic data, such as maximum flow rate and maximum detrusor pressure 5

Predictive Factors for Perinephric Stranding

Several predictive factors for perinephric stranding have been identified, including:

• Inflammation markers, such as neutrophil-lymphocyte ratio and systemic immune-inflammation index 6
• Radiologic findings, such as Hounsfield unit (HU) of perinephric fat and renal parenchyma 6
• History of nonsterile urine culture and diabetes mellitus (DM) 6