Most pyelonephritis needs no imaging; imaging is for the patient who does not improve, is diabetic, obstructed or septic — to find obstruction, abscess or emphysematous change.
Orient first
- Imaging is indicated for failure to respond in 48–72 h, sepsis, suspected obstruction, diabetes or immunosuppression.
- CT shows striated or wedge-shaped hypoenhancement in the nephrographic phase; ultrasound is often normal.
- Abscess (a rim-enhancing collection) and obstruction (a stone) change management — drainage.
Acquire the study
- Unenhanced and nephrographic phases; coronal reformats.
The manoeuvre
- Nephrographic phase: striated nephrogram or wedge-shaped hypoenhancing areas.
- Renal abscess: rim-enhancing low-attenuation collection; measure in cm.
- Unenhanced series: obstructing stone; hydronephrosis.
- Perinephric stranding and fluid; gas (emphysematous).
What confirms it
- Compatible imaging in a patient with the clinical and urinary picture.
What licenses you to exclude it
- Imaging cannot exclude pyelonephritis; it excludes obstruction and abscess.
The classic misread
- Calling a wedge-shaped defect infarct — look for the cortical rim sign.