Perinephric abscess

Background

• An abscess of the perinephric fat that abuts the renal cortex
• Can arise as a complication either a pre-existing pyelonephritis (majority) or from hematogenous seeding

Causative Organisms

• E. coli (51.4%)
• S. aureus (10%)

Perinephric vs renal abscess

	Perinephric	Renal
Necrotic Area	Perinephric fat between the renal cortex and Gerota's fascia	Renal parenchyma
Cause	Pyelonephritis (majority)	Pyelonephritis (vast majority)
Risk of morbidity	Higher	Lower

Clinical Features

• Sign/symptoms similar to pyelo (fever, CVAT, dysuria)
• Occurs in setting of ascending infection with obstructed pyelo

Differential Diagnosis

Dysuria

• Genitourinary infection
  • Acute cystitis ("UTI")
  • Pyelonephritis
  • Urethritis
  • Chronic cystitis
  • Infected nephrolithiasis
  • Prostatitis
  • Epididymitis
  • Renal abscess/perinephric abscess
  • Emphysematous pyelonephritis
• Nephrolithiasis
• Urethral issue
  • Urethritis
  • Urolithiasis
  • Urethral foreign body
  • Urethral diverticulum
  • Allergic reaction (contact dermatitis)
  • Chemical irritation
  • Urethral stricture or obstruction
  • Trauma to vagina, urethra, or bladder
• Gynecologic
  • Vaginitis/cervicitis
  • PID
  • Genital herpes
  • Pelvic organ prolapse
  • Fistula
  • Cystocele
• Other
  • Diverticulitis
  • Interstitial cystitis
  • Behavioral symptom without detectable pathology

Evaluation

Laboratory Testing

• CBC - Although it is a non-specific finding, a leukocytosis is typically seen.
• Chemistry Panel - Lactic acidosis is a common finding and is seen earlier in the disease course in diabetic patients. Renal insufficiency is also commonly seen as well.
• Urinalysis - Will often show evidence of pyelonephritis, however if the perinephric abscess is secondary to hematogenous spread, the urine could be sterile. Therefore a negative U/A does NOT rule out a perinephric abscess.
• Blood and urine cultures

Imaging

• X-ray - Will sometimes show abnormalities that might suggest a perinephric abscess is present, however one or all of these findings may not be present, therefore it is suggested to use more invasive imaging to rule out a perinephric abscess if clinical suspicion is high. Abdominal X-ray findings that can suggest a perinephric asbcess include:
  • Displaced or rotated kidney
  • Scoliosis - Deviation of the spine will occur in the direction of the lesion
  • Loss of the psoas margin, however the false positivity rate is about 10%
  • An abdominal mass or displaced bowel gas
  • Thoracic pathology - ipsilateral consolidative process, atelectasis, or pleural effusion
  • Ultrasound - A fluid filled mass extending from the renal cortex into the perinephric fat can be seen.
  • CT - Is the imaging modality of choice for evaluation of suspected perinephric abscess. Sensitivity of detecting a perinephric abscess is about 90%. CT can give an accurate measurement of the abscess and can also show involvement, if any, of any surrounding structures (liver, ipsilateral psoas muscle, vertebral bodies, intervertebral discs, etc.)
  • MRI - Has limited utility in the Emgergency Room setting given the time it takes for the study to be completed and read. However, advantages over CT include better delineation of soft tissue structures (listed above), absence of radiation exposure, and better contrast sensitivity.

Management

• Antibiotic therapy depends on the suspected cause
  • Pyelonephritis (enterobacteriaceae): third generation cephalosporin + quinolone
  • Hematogenous (staphylococcus)): vancomycin
  • Known to be colonized by ESBL: carbapenem
• Abscess drainage
  • Abscess of ANY size requires IR for percutaneous drainage
  • If any urological obstruction is suspected (nephrolithiasis, ureterolithiasis, external compression from abdominal cavity, presence of pre-existing ureteral stent), emergent urological consultation should be obtained

Disposition

• Admission

See Also

• pyelonephritis
• Emphysematous pyelonephritis
• Renal abscess
• Urolithiasis