Genitourinary Radiology > Kidneys > Parenchymal > Large Kidney > Pyelonephritis



Pyelonephritis is a bacterial infection of the renal parenchyma and collecting system, a clinical diagnosis based on fever, flank pain, costovertebral angle tenderness, and urinary tract infection.

Imaging is rarely required for diagnosis, but may be helpful if a more complicated infection, such as a renal abscess, is suspected. CT findings include renal enlargement with wedge-shaped heterogeneous areas of poor enhancement, known as a “striated nephrogram”.

Contrast enhanced CT scan in patient with fever and flank pain shows ill defined linear enhancement abnoramlity in the left mid pole arteriorly (arrows) known as "striated nephrogram" which is a finding seen in acute pyelonephritis. Importantly, no complications of pyelonephritis are noted (e.g., no renal abscess).

Gray scale ultrasound image in a similar patient as the CT scan above. Notice the focal area of increased echogenicity (brightness) in the right upper pole cortex (arrows). This is a non specific finding but in a patient with symptoms of UTI, this finding is consistent with focal pyelonephritis.

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