Diagnostic Ultrasound - Abdomen and Pelvis

Renal Abscess
Diagnoses: Urinary Tract
TERMINOLOGY
• Purulent &/or necrotic intraparenchymal or perinephric
collection arising from unresolved pyelonephritis
IMAGING
• 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 gasforming
organisms within abscess
PATHOLOGY
• Ascending urinary tract infections (80%)
○ Corticomedullary abscess by Escherichia coli or Proteus
species
KEY FACTS
• Hematogenous spread (20%)
○ Cortical abscess by Staphylococcus aureus
CLINICAL ISSUES
• 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
DIAGNOSTIC CHECKLIST
• Many abscesses appear mass-like and may mimic
neoplasms but are usually associated with > 1-week history
of infection, minimal internal vascularity, and associated
inflammatory changes
(Left) Graphic shows a pusfilled
cavity within the renal
parenchyma and purulent
material in the perinephric
space st. (Right) Transverse
and longitudinal images of the
kidney show a wellcircumscribed,
hypoechoic
mass in the posterior kidney
. Note the posterior
acoustic enhancement ſt.
(Left) Color Doppler US shows
lack of vascularity within a
lower pole hypoechoic mass
(abscess collection) . Note
the echogenic surrounding fat,
indicative of perinephric
inflammation ſt. (Right) T1
C+ FS MR in the same patient
shows an irregular lower pole
mass containing multiple rimenhancing
locules . Because
of the resemblance to cystic
renal neoplasm, biopsy was
performed and abscess was
confirmed. However, note the
inflammatory change in the
anterior pararenal space ,
favoring infection.
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