Mediquest - November '07 Edition

Lab Studies:

1. Basic laboratory data are variable. However, most patients demonstrate a leukocytosis with a left shift on CBC and differential. Anemia may be present in patients with chronic infection.
2. Urinalysis also shows signs of infection
3. Conduct an electrolyte analysis. BUN and creatinine levels are often elevated.
4. With corticomedullary abscess, Pyuria and proteinuria are common.
5. Cultures:
A. Urine and blood culture results are often positive.
B. The most common pathogens recovered in affected patients are E coli, P.Mirabilis, and Klebsiella species.
C. Blood cultures are positive in more than 50% of patients
D. However, bacteruria and pyuria may be absent if the ureter is completely obstructed.
6. Imaging Studies:
1. Renal ultrasonography and CT scanning are the fundamental tests for diagnosing corticomedullary abscesses.
2. CT scanning is, the most useful modality in diagnosing intrarenal abscess and in planning operative procedures for treatment. Non-contrast CT scanning is a poor study for demonstrating intrarenal abscesses. When a CT scan is obtained in a clinical situation and a renal abscess is suspected, obtain both contrast and noncontrast images for comparison purposes.
CT scanning is extremely useful to aid in characterizing renal infections, as diffuse or focal, to detect the presence of gas, and to help the clinician determine whether perinephric extension exists. CT scanning typically shows a poorly defined, wedge-shaped, hypodense area that may involve liquefaction.
3. Ultrasonographic findings are less specific than findings on CT scanning, and MRI usually offers no additional information compared to CT scanning.
4. Other imaging studies, are KUB radiography and Intravenous pyelography,..These are however often not helpful in identifying intrarenal abscess;

Treatment :

1. Medical therapy:

A. Treatment of acute focal and multifocal pyelonephritis with appropriate antibiotics should produce a clinical response within 1 week of initiating therapy in most patients. However, well-established large abscesses are often difficult to treat with antibiotics alone.
B. In most patients, attempt an intensive trial of appropriate antibiotics directed against culture-specific bacteria before attempting surgical drainage.
C. If corticomedullary abscess is suspected, promptly administer parenteral antibiotics and intravenous hydration.
D. Antibiotics -- Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.

If choosing a combination therapy, use a beta-lactam antibiotic administered intravenously withan aminoglycoside or fluroquinolone. Administer this line of therapy until culture and sensitivity results are received and then modify the antimicrobial therapy to the most appropriate agent.
Duration of therapy is not well defined. Continue parenteral antibiotics for at least 24-48 hours after patient symptoms clinically improve and the fever resolves. Then, administer a suitable oral agent and continue for an additional 2-4 weeks, as determined by complete clinical and radiographic resolution of the intrarenal process. Acute focal bacterial nephritis usually responds to antimicrobial therapy alone. Follow-up radiographic studies typically show complete resolution of the intrarenal lesion.

Conversely, patients with acute multifocal bacterial nephritis take longer to improve with antibiotics alone. Occasionally, patients may require some form of a drainage procedure.

FAILURE OF ANTIMICROBIAL THERAPY :

Predisposing factors for patients in whom antibiotic therapy fails include
A.elderly age
B.diabetes mellitus
C.large abscesses
D. Obstructive uropathy
E.anatomic abnormalities
F. advanced disease
G. impaired renal function at presentation
H. urosepsis.

2. Surgical therapy:

Historically, surgical debridement, drainage, and nephrectomy were widely used to treat corticomedullary abscesses. With the advent of effective antibiotics along with percutaneous techniques, the open surgical approach is now reserved for more severe, refractory cases.

3. Abscess drainage

Generally, large intrarenal abscesses require drainage if the patient has persistent fever and absence of clinical improvement after 1 week of appropriate antimicrobial therapy. Renal abscesses may be drained percutaneously under CT or ultrasonographic guidance. If perirenal abscess or infected urinoma is present, also place a percutaneous perirenal drain.

Leave the drainage tube in place until the patient is afebrile and stable. Leave the drain in situ until the output from the drain becomes minimal. If the patient requires open surgical drainage, proceed with exploration and drainage. Irrigate the infected renal fossa copiously with antibiotic irrigant and leave perirenal drains.

COMPLICATION :
The most feared complication of corticomedullary abscess is potential extension of the abscess through the renal capsule, resulting in a perinephric abscess. Gerota fascia usually contains the abscess within the perinephric space, but the process may extend into the retroperitoneum to infect adjacent structures. In these situations, simple nephrectomy is quite challenging because adjacent organs, such as the pancreas and bowel, may be involved.

4. Nephrectomy

Reserve nephrectomy for patients with diffusely damaged renal parenchyma or patients who are septic and require urgent intervention for survival.

Following nephrectomy, prognosis is excellent in patients without other urinary tract pathology.

5. Follow-up care:

• Instruct the patient to return to the clinic in 1-2 weeks for follow-up examination.
• Check wound for signs of surgical site infection.
• Remove staples or sutures.
• Obtain a follow-up contrast CT scan to ensure resolution of renal parenchymal abnormalities.
• Following surgery, inform the patient that normal activities can resume in 4-6 weeks.