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Pyelonephritis


KEY FACTS

Terminology

  • Acute infection of renal parenchyma; often difficult to clinically distinguish from lower UTI

Imaging

  • Imaging work-up of UTI controversial

    • See professional society guidelines

  • With pyelonephritis, marked inflammatory response to renal parenchymal infection causes swelling that alters normal tissue properties & effectively ↓ radiologic contrast agent delivery to site, which results in

    • ↓ uptake on nuclear cortical scan

    • ↓ perfusion on Doppler imaging with altered echotexture on grayscale US

    • Striated or wedge-shaped foci of ↓ enhancement on CECT/MR

  • US with Doppler least invasive & readily available but less sensitive than nuclear renal cortical scans, CT, & MR

  • US frequently performed to search for associated complications (abscess, stones, scarring), congenital anomalies, & hydronephrosis

Clinical Issues

  • Symptoms nonspecific: Malaise, irritability, fever, abdominal/flank pain, vomiting, hematuria, dysuria, change in urinary habits/enuresis, strong-smelling urine

  • Treatment: 7- to 14-day course of antimicrobial therapy; may be started IV & changed to oral

    • Obtain work-up for vesicoureteral reflux (VUR) & congenital anomalies

      • –

        Pyelonephritis associated with VUR in ∼ 25-40%

  • Complications: Perirenal abscess, necrotizing papillitis, pyonephrosis (obstruction), & cortical scarring

    • Permanent scarring more likely < 2 years old

    • Recurrent infections & scarring can lead to hypertension &/or end-stage renal disease

Transverse US of the mid right kidney
shows a focus of increased echogenicity
with loss of normal corticomedullary differentiation, typical of pyelonephritis.

Transverse color Doppler US of the same right kidney
shows decreased perfusion
in the area of pyelonephritis due to marked swelling & inflammatory response.

Coronal CECT image in a 13 year old scanned for possible appendicitis shows focal decreased enhancement
in the left renal lower pole with adjacent fat stranding, consistent with pyelonephritis.

Posterior pinhole images from Tc-99m DMSA renal cortical scintigraphy show absent radiotracer in the lower pole of the right kidney
in a patient with acute pyelonephritis. Large, wedge-shaped photopenic areas suggest pyelonephritis, while smaller, crescent-shaped cortical defects suggest scarring.

TERMINOLOGY

Synonyms

  • Acute lobar nephronia, focal bacterial nephritis

Definitions

  • Acute infection of renal parenchyma

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