Diagnosis
A late complication of urinary tract infections and pyelonephritis.
Epidemiologic Risks
Having pyelonephritis.
Occasionally benign renal cysts will get infected, in polycystic disease, it can be difficult to know which one unless you do at PET scan (PubMed).
Microbiology
Whatever is the cause of the UTI/pyelonephritis.
Empiric Therapy
Drain and treat for whatever is causing, can I hear you say it, the UTI/pyelonephritis.
If the abscess is < 5 cm, antibiotics alone will cure it (PubMed).
Duration? Until it is gone. Use IV until afebrile, then po is sensitivities allow.
Drain large abscesses or non-responders. "Factors associated with antimicrobial treatment failure are large abscesses, obstructive uropathy, severe vesico-ureteral reflux, diabetes, old age and urosepsis with gas forming organisms (PubMed)."
Pearls
Usually, it manifests with fevers greater than 5 days on appropriate therapy for, say it again, pyelonephritis. CT or US makes the diagnosis. Then drain it if > 5 cm or so.
There is also the lobar nephronia/acute focal bacterial nephritis, which sounds like an ancient instrument, but is a focal 'cellulitis' of the kidney, a mass due to acute focal infection without liquefaction and can be mistaken as a tumor.
Acute focal bacterial nephritis can be missed with ultrasound (PubMed) but found on CT or MRI. It may need a longer course of therapy, like 3 weeks (PubMed).
Last Update: 12/28/18.