Mary K. Powers, MD
Raju Thomas, MD, MHA, FACS
BASICS
DESCRIPTION
• Renal abscess/carbuncle:
– Collection of purulent material confined to the renal parenchyma
• Perirenal abscess:
– Results from extension of an acute cortical abscess into the perinephric space; confined by Gerota fascia
• Pararenal/perinephric abscess:
– Results from the rupture of a perinephric abscess through Gerota fascia into the pararenal space
EPIDEMIOLOGY
Incidence
Perinephric and renal abscesses are uncommon but potentially lethal complications of UTI
Prevalence
• 2/3 of gram-negative abscesses are associated with renal calculi or kidneys with poor function
• Pregnant women with untreated bacteriuria are associated with a higher incidence of pyelonephritis and subsequent diagnosis of abscess
• Renal infection is among the most common sites for extrapulmonary disease in patients with TB
RISK FACTORS
Diabetes mellitus, polycystic kidney disease, hemodialysis, neurogenic bladder, IV drug users, tuberculosis, recurrent urinary tract infection and/or pyelonephritis, nephrolithiasis, vesicoureteral reflux, ureteropelvic junction obstruction or other source of obstruction, any immunocompromised state
Genetics
N/A
PATHOPHYSIOLOGY
• Gram-negative organisms have been implicated in the majority of adults with renal abscesses (Escherichia coli, Proteus mirabilis, and Staphylococcus aureus) account for the majority of infections (in descending order of occurrence) (1)
• Hematogenous renal seeding by gram-negative organisms may occur, but this is not likely to be the primary pathway for gram-negative abscess formation
• Hematogenous renal seeding: Skin infection with gram-positive organisms, IV drug abuse, immunocompromised status
• Ascending infection associated with tubular obstruction from prior infections, vesicoureteral reflux, or calculi appears to be the primary pathway for the establishment of gram-negative abscesses
ASSOCIATED CONDITIONS
See “Risk Factors" above
GENERAL PREVENTION
Increased clinical suspicion, prompt recognition, and treatment of infection, especially in the face of obstruction in high-risk patients
DIAGNOSIS
HISTORY
• Significant chronic or acute illnesses including diabetes, neurogenic bladder dysfunction, chronic renal failure, hemodialysis, and polycystic renal disease
• Renal calculi
• IV drug abuse
– Gram-positive source of infection 1–8 wk before the onset of urinary tract symptoms
Preceding infection can occur in any area of the body (eg, skin lesions, dental infections)
• Patients with UTI and abdominal or flank mass
• Persistent fever with suspected genitourinary source after 3–5 days of antimicrobial therapy
PHYSICAL EXAM
• Elevated temperature
• CVA or flank tenderness
• Abdominal and/or flank mass
• Distended or palpable bladder
• Look for skin carbuncles or dermatologic evidence of IV drug abuse
• Heart murmurs
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Serum creatinine:
– Variable findings, dependent on concurrent obstruction and underlying renal dysfunction
• CBC:
– Patients typically have marked leukocytosis
• Urine analysis:
– Pyuria and bacteria often present, although pyuria/bacteriuria may not be evident unless the abscess communicates with the collecting system
– Sterile pyuria often seen with TB
• Urine culture:
– When abscesses contain gram-negative organisms, urine culture often demonstrates the same organism isolated from the abscess
– Since gram-positive organisms are most commonly blood borne, urine cultures in these cases typically show no growth or a microorganism different from that isolated from the abscess
– Catheterized urine collection recommended for female patients
• Blood cultures:
– Gram-negative organisms are most commonly cultured
– Gram-positive organisms are not routinely similar to those cultured from abscess
Imaging
• Differentiation between early renal abscess and acute pyelonephritis is difficult due to small size
• Abdominal CT:
– Diagnostic procedure of choice
– Can often delineate the route of spread of infection into surrounding tissues
– Abscesses are characteristically well defined both before and after contrast agent enhancement
– Acute findings include renal enlargement and focal, rounded areas of decreased attenuation
– Chronic findings include obliteration of adjacent tissue planes, thickening of Gerota (perinephric) fascia, a round or oval parenchymal mass of low attenuation, and a surrounding inflammatory wall of slightly higher attenuation that forms a ring when the scan is enhanced with contrast material (ring sign)
– See Figure 1, Renal Abscess
• IV urography (if performed)
– Abnormal in up to 80% of patients, although findings often are nonspecific
– Generalized enlargement of involved renal unit with distortion of renal contour and collecting system
– Absence of psoas shadow on affected side
– Bubbles of extraluminal gas can be seen surrounding the kidney in large perinephric abscesses
• Abdominal US:
– Quickest and least expensive diagnostic imaging study
– Common findings include an echo-free or low-echodensity space-occupying lesion with increased transmission, which is poorly marginated during the acute phase
– Well-defined discrete lesion during chronic stages, which is difficult to distinguish from a renal mass
ALERT
Evidence of air within renal parenchyma tissue is diagnostic for emphysematous pyelonephritis which may require urgent surgical intervention. See Section I: Emphysematous pyelonephritis.
Diagnostic Procedures/Surgery
CT- or US-guided needle aspiration may be necessary to differentiate an abscess from a hypervascular tumor; aspirated material can be collected for culture to guide appropriate antimicrobial therapy. A percutaneous drain may be left in place and clinical course can be evaluated.
Pathologic Findings
Abscess fluid will demonstrate neutrophils and gram stain will reveal bacteria
DIFFERENTIAL DIAGNOSIS
• Pyelonephritis (2)
• Pyonephrosis
• Xanthogranulomatous pyelonephritis
• Emphysematous pyelonephritis
• Renal TB
• Bowel perforation with retroperitoneal spread of infection
TREATMENT
GENERAL MEASURES (3,4)
• Hospitalization with initiation of IV antibiotics and fluid resuscitation.
• Suspected pyelonephritis treated with antibiotics for 48–72 hr without significant improvement requires radiographic evaluation to rule out obstruction and/or abscess formation.
• Recent evidence indicates that for very small (<3-cm abscesses), careful observation and IV-tailored antimicrobial agents may obviate surgical procedures.
• Abscesses 3–5 cm in diameter and smaller abscesses in immunocompromised hosts or those that do not respond to antimicrobial therapy should be drained percutaneously.
• Surgical drainage, however, currently remains the procedure of choice for most renal abscesses >5 cm in diameter or if perirenal extension of abscess occurs.
• Obstruction, if present, must be relieved.
MEDICATION
First Line
• Antibiotic therapy: May prevent surgical intervention unless abscess involves perinephric space.
• Initiate empiric treatment with fluid resuscitation and broad-spectrum IV antibiotics.
– 3rd-generation cephalosporins
Cefotaxime—1–2 mg IV/Q8–12h
Ceftriaxone—1–2 mg IV/Q24h
Ceftazidime—1 g IV/Q8–12h
– Aminoglycosides
Gentamicin—1–1.7 mg/kg IV/Q8h
Amikacin—7.5 mg/kg IV/Q12h
Tobramycin—1–1.7 mg/kg IV/Q8h
– Antipseudomonal penicillins
Piperacillin/Tazobactam—3.375 g IV/Q6h
Ticarcillin/Clavulanate—3.1 g IV/Q4–6h
• IV antibiotics until afebrile for 24–48 hr, switch to PO for at least 2 wk based on culture.
• Adjust dose for renal function.
Second Line
• For a suspected hematogenous source, expand coverage to include penicillin-resistant Staphylococcus.
– Vancomycin—1 g IV/Q12h
SURGERY/OTHER PROCEDURES
• Standard treatment for renal abscesses >5 cm or those that fail to respond to percutaneous drainage and IV antibiotic therapy has been rapid incision and drainage.
• Relief of coexisting obstruction is mandatory.
• Primary treatment remains drainage for all perinephric abscesses.
• Nephrectomy may be required for adequate treatment if medical therapy/incision and drainage fails.
ADDITIONAL TREATMENT
Radiation Therapy
N/A
Additional Therapies
CT- or US-guided placement of percutaneous drains with concurrent IV antibiotic therapy is currently an accepted method of treatment for abscesses 3–5 cm in size and smaller abscesses in immunocompromised patients who fail to respond to medical therapy.
Complementary & Alternative Therapies
N/A
ONGOING CARE
PROGNOSIS
• Perinephric abscess is historically associated with mortality rates approaching 39–50%.
• Recent series with prompt implementation of IV antibiotics and subsequent percutaneous or surgical drainage report mortality rates of 5–12%.
COMPLICATIONS
• Delay in diagnosis is associated with higher mortality rate.
• Delay in diagnosis and treatment is associated with loss of renal function and, in rare circumstances, genitourinary fistulas to the pleura, colon, skin, etc.
FOLLOW-UP
Patient Monitoring
• Address the underlying medical conditions to prevent recurrent infections.
• Repeat radiographic studies to confirm complete resolution.
• Extended antibiotic therapy is often required.
Patient Resources
• Medline Patient Information:
– http://www.nlm.nih.gov/medlineplus/ency/article/001274.htm
• Urology Care Foundation Patient Guide:
– http://www.urologyhealth.org/urology/index.cfm?article=18
REFERENCES
1. Gardiner RA, Gwynne RA, Roberts SA. Perinephric Abscess. BJU Int. 2011;107(Suppl 3):20–23.
2. Shields J, Maxwell AP. Acute pyelonephritis can have serious complications. Practitioner. 2010;254(1728):19, 21, 23–24, 2.
3. Ko MC, Liu CC, Liu CK, et al. Incidence of renal and perinephric abscess in diabetic patients: A population-based national study. Epidemiol Infect. 2011;139(2):229–235.
4. Heller MT, Haarer KA, Thomas E, et al. Acute conditions affecting the perinephric space: Imaging anatomy, pathways of disease spread, and differential diagnosis. Emerg Radiol. 2012;19(3):245–254.
ADDITIONAL READING
• Meng MV, Mario LA, McAninch JW. Current treatment and outcomes of perinephric abscesses. J Urol. 2002;168(4 Pt1):1337–1340.
• Tanagho EA, McAninch JW. Smith’s General Urology. 17th ed. New York, NY: McGraw Hill; 2008.
See Also (Topic, Algorithm, Media)
• Pyelonephritis, Acute
• Pyelonephritis, Chronic
• Pyelonephritis, Emphysematous
• Pyelonephritis, Xanthogranulomatous
• Pyonephrosis
• Renal and Perirenal Abscess Image 
• Retroperitoneal Abscess
CODES
ICD9
• 590.2 Renal and perinephric abscess
• 590.80 Pyelonephritis, unspecified
• 592.0 Calculus of kidney
ICD10
• N12 Tubulo-interstitial nephritis, not spcf as acute or chronic
• N15.1 Renal and perinephric abscess
• N20.0 Calculus of kidney
CLINICAL/SURGICAL PEARLS
• Abscesses <3 cm can be managed with medical treatment initially.
• Continued fevers require surgical drainage of abscess.
• Include gram-positive antibiotic coverage if suspect hematogenous spread (IV drug use).