Flank pain with fever, suspected complicated pyelonephritis
Recommended: CT Abdomen / Pelvis with IV contrast is the preferred imaging study for flank pain with fever, suspected complicated pyelonephritis. Uncomplicated pyelonephritis is treated empirically without imaging.
Recommended study
CT Abdomen / Pelvis with IV contrast
Uncomplicated pyelonephritis is treated empirically without imaging. Image for: failed therapy, diabetes, immunocompromise, stones, recurrent infection, sepsis, or signs of obstruction.
If the default doesn't apply
Pregnancy
US
Renal/bladder Ultrasound first
No contrast
Stone with obstruction concern
CT
Non-contrast CT abdomen/pelvis (stone protocol)
No contrast
Watch-outs
Emphysematous pyelonephritis
Gas in renal parenchyma — urological emergency; mortality up to 50% without urgent drainage / nephrectomy.
Obstructed infected system
Pyonephrosis requires emergent decompression (PCN or ureteral stent) regardless of antibiotic timing.
Pearls
- Routine pyelonephritis is treated empirically — imaging only when failure to improve in 48–72h or red flags.
- Look for striated nephrogram, perinephric stranding, focal hypoenhancement (focal pyelonephritis / nephronia).
- Renal abscess > 3 cm typically requires drainage in addition to antibiotics.