renal abscesses and perinephric abscesses

introduction

renal abscesses and perinephric abscesses generally present as flank pain with fever and markedly raised inflammatory markers such as C reactive protein (CRP)
they may present insidiously, particularly in the elderly, diabetcis or chronic alcoholism who may have autonomic neuropathy
the urine culture may be NAD if it is haematogenous spread of infection instead of the more usual ascending UTI aetiology
haematogenous spread abscesses are primarily perinephric or arise in the cortex of the kidney (not the medulla)
perinephric abscesses occur in the space confined by Gerota's fascia
- these may spread into:
  - the retroperitoneum
  - the collecting system of the kidney
  - the flank muscles
  - the psoas muscle
  - the groin
  - the paravesicle region
  - the peritoneum (uncommmon)
  - the subdiaphragmatic region to for a subphrenic abscess and then even into the thoracic cavity to form an empyema or even a nephrobronchial fistula
  - the colon
diagnosis is generally made by the finding of a mass in the kidney or near the kidney (perinephric) on CT KUB scan, however, a contrast CT scan is preferable.

renal malignancies
acute lobar nephronia
- focal region of interstitial nephritis causing a renal mass which is an intermediate state between acute acute pyelonephritis and renal abscess
malakoplakia - inflammatory reaction due to E.coli infection

assumes a mass has been detected on CT scan
urgent referral to urology
- early percutaneous drainage and culture is generally indicated for:
  - renal abscesses > 5cm
  - all perinephric abscesses
  - for cases not responding to antibiotics
  - severe sepsis
for perinephric abscesses:
- if prompt drainage is feasible, ideally drainage should be performed prior to initiation of antimicrobial therapy, so that Gram stain and culture results can be used to guide selection of therapy
- empiric antibiotic Rx of cases with presumed haematogenous cause should cover Staph. aureus
if unwell, manage as per sepsis / septicaemia with early iv antibiotic and iv fluid resuscitation