Purulent &/or necrotic intraparenchymal or perinephric collection arising from unresolved pyelonephritis

Complex cystic mass, may be sharply marginated or more permeative

Rim may be hypervascular, or vessels may course to edge of lesion and stop

Findings of pyelonephritis (renal enlargement, lack of corticomedullary differentiation, and urothelial thickening) may be present

Internal echogenic foci with “comet tail” may represent gas-forming organisms within abscess

Ascending urinary tract infections (80%)

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  Corticomedullary abscess by Escherichia coli or Proteus species

Hematogenous spread (20%)

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  Cortical abscess by Staphylococcus aureus

Abscess emerges after 10-14 days of untreated or undertreated urinary tract infection, not on 1st day of symptoms

Antibiotic therapy, usually IV ± percutaneous drainage

Surgical drainage or nephrectomy are rarely needed

Many abscesses appear mass-like and may mimic neoplasms; careful evaluation with color Doppler may show minimal internal vascularity

Look for surrounding echogenic fat, which indicates associated inflammatory changes

Because findings can be subtle, change scanning windows and alter phase of respiration while scanning to help attain best image