Is perinephric fat stranding a normal finding in patients with nephrolithiasis (kidney stones) and hydronephrosis?

From the Guidelines

Perinephric fat stranding can be a normal finding in patients with nephrolithiasis (kidney stones) and hydronephrosis, as it is often seen in cases of acute kidney obstruction or inflammation, which commonly occur with these conditions. Perinephric fat stranding refers to increased attenuation in the fat surrounding the kidney on CT imaging, and it is often associated with the backup of urine (hydronephrosis) and increased pressure within the kidney that can occur when a kidney stone blocks the ureter 1. When evaluating patients with symptomatic hydronephrosis, CT abdomen and pelvis without IV contrast can be a useful diagnostic tool, particularly when obstructive urolithiasis is a primary concern, as it can help identify the presence of a ureteral stone and predict the likelihood of stone passage failure 1. Some studies have found that the presence of hydronephrosis on ultrasound or CT can be a supportive finding in the diagnosis of obstructive urolithiasis, and that the degree of hydronephrosis can correlate with the severity and acuity of the obstruction 1. However, it's essential to note that perinephric fat stranding is not specific to kidney stones and hydronephrosis, and other causes of kidney inflammation or infection can also produce this imaging finding, highlighting the need for clinical correlation and additional diagnostic tests for a definitive diagnosis. Key points to consider when evaluating perinephric fat stranding in patients with kidney stones and hydronephrosis include:

• The degree of fat stranding often correlates with the severity and acuity of the obstruction
• Mild stranding may be seen with partial obstructions, while more extensive stranding can indicate a complete obstruction or infection
• Clinical correlation and additional diagnostic tests are often necessary for a definitive diagnosis
• CT abdomen and pelvis without IV contrast can be a useful diagnostic tool in evaluating patients with symptomatic hydronephrosis, particularly when obstructive urolithiasis is a primary concern 1.

From the Research

Perinephric Fat Stranding in Nephrolithiasis and Hydronephrosis

• Perinephric fat stranding is a finding that can be observed on computed tomography (CT) scans in patients with various conditions, including nephrolithiasis (kidney stones) and hydronephrosis.
• According to a study published in 2002 2, perinephric fat stranding was found to be a significant predictor of "any degree of obstruction" in patients with urinary lithiasis, with an odds ratio of 6.15.
• Another study published in 2019 3 found that peri-renal fat stranding was associated with the onset of obstructive pyelonephritis in patients with obstructive urolithiasis, with a p-value of 0.02.

Clinical Significance of Perinephric Fat Stranding

• The presence of perinephric fat stranding on CT scans may indicate inflammation or infection in the perinephric area, which can be associated with conditions such as pyelonephritis.
• A study published in 2019 4 found that the presence of perinephric fat stranding in patients with acute pyelonephritis predicted bacteraemia, with a significantly higher rate of bacteraemia in the PFS group compared to the non-PFS group.
• However, it is essential to note that perinephric fat stranding can also be observed in patients without infection or inflammation, and its presence should be interpreted in the context of other clinical and radiological findings.

Limitations and Variability

• The studies reviewed showed considerable interobserver variability in the diagnosis of perinephric fat stranding on CT scans, with kappa values ranging from 0.26 to 0.60 2.
• The clinical significance of perinephric fat stranding may vary depending on the underlying condition and the presence of other symptoms and findings.