Woman in pain.
Key Points - Renal abscess:
- Occur 1-2 weeks after infection
- Ascending UTI in 80%
- Gram negative organisms
- Abscess usually forms at corticomedullary junction
- UTI to acute pyelonephritis or acute focal bacterial nephritis to liquefaction to sequestration to renal abscess
- Hematogenous spread in 20%
- IVDU and skin infection
- Other infected sites
- Iatrogenic cause
- Gram positive and negative bacteria
- Usually form in cortex
- Fevers, flank/abdominal pain, chills, dysuria, leukocytosis, positive UA/urine culture
- 2% of all renal masses
- 20-60% have urolithiasis
- Risk factors: long term dialysis, DM, IVDA
- Complications:
- Can lead to perinephric abscess or go beyond Gerota fascia and become a paranephric abscess and even spread into peritoneal cavity. Rupture into renal collecting system is pyonephrosis.
- Treatment:
- Treat with antibiotics, but if abscess not resolved in 48hours or "ripe" with well defined walls do percutaneous aspiration and drainage with CT or US. If percutaneous treatment fails, need open drainage or nephrectomy.
Radiologic overview of the diagnosis:
- Best imaging: CT with and without intravenous contrast
- Spherical nonenhancing renal mass with perinephric stranding on CECT is best diagnostic clue.
- NECT:
- Single or multiple round well-marginated low attenuating masses with or without gas collection
- CECT:
- Enlarged kidney with focal areas of hypoattenuation in acute phase or "rim or ring sign" in subacute of chronic phase (enhancement of wall).
- No central enhancement.
- Obliterated renal sinus or calyceal effacement.
- Thick walls and mild dilated renal pelvis and ureter.
- Perinephric extensions+ indistinct renal outline, edema/obliterated perinephric fat, thick gerota fascia and perinephric septa.
- MRI:
- T1: Hypointense mass
- T2: Hyperintense mass with increased signal around the mass
- T1 + contrast: rim enhancement if >1cm
- US:
- Anechoic or hypoechoic to echogenic fluid collection
- Mass in or displacing the kidney
- Round thick or smooth-walled complex mass
- Low level internal echoes
- "Comet sign"= internal echogenic foci due to gas with posterior "dirty" shadowing.
- Septations possible.
Key points:
- 2% of renal masses are abscesses
- Occur 1-2 weeks after initial infection, most commonly UTI
- Best seen with CT without and with intravenous contrast
- Rim of enhancement indicates subacute or chronic phase which indicates percutaneous drainage or open surgery
References:
- Statdx. Abscess, Renal. Accessed 3/16/2011.
