Disclosure
A perinephric abscess is a collection of suppurative material in the perinephric space. A perinephric abscess can pose a great diagnostic challenge, even to an astute clinician. This is very important because a delay in diagnosis leads to higher morbidity and mortality. Newer renal imaging tools, especially CT scanning and ultrasonography, have allowed for an early and accurate diagnosis, and newer antibiotics have been helpful in the appropriate treatment during the last 3 decades. Problem: A perinephric abscess is a collection of purulent material around the kidneys, with a presentation that is insidious (>14 d). This abscess formation occurs secondary to urinary obstruction and/or hematogenous spread. Frequency: Perinephric abscess is an uncommon complication of urinary tract infections. The incidence ranges from 1-10 cases for every 10,000 hospital admissions. Men and women are affected with equal frequency. Etiology: Escherichia coli, Proteus species, and Staphylococcus aureus are the usual etiologic organisms. The use of antibiotics for skin and wound infections also has decreased the incidence of staphylococcal infection from 45% to 6% over the last 6 decades. However, this rate has increased from 8% to 30% for E coli infections and from 4% to 44% for Proteus mirabilis infection. Other gram-negative bacteria that can cause this infection are Klebsiella, Enterobacter, Pseudomonas, Serratia, and Citrobacter. Occasionally, the infection can occur from enterococci infection. One case caused by Streptococcus pneumoniae infection has been reported. Anaerobes such as Clostridium, Bacteroides, and Actinomyces may account for some of the culture-negative abscesses. Other causes include fungi, especially Candida species, and Mycobacterium tuberculosis. Multiple bacteria can be present in as many as 25% of cases. Perinephric abscess secondary to Candida infection usually occurs in patients with diabetes. Predisposing factors include surgery (including renal transplantation) and prolonged antibiotic therapy. Pathophysiology: Perinephric abscesses are located between the capsule of the kidney and the Gerota fascia. The abscesses remain confined in this location because of the Gerota fascia. Perinephric abscesses usually occur because of disruption of a corticomedullary intranephric renal abscess, recurrent pyelonephritis, xanthogranulomatous pyelonephritis, or an obstructing renal pelvic stone causing pyonephrosis. Approximately 30% of cases are attributed to hematogenous dissemination of organisms from sites of infection such as wound infection, furuncles, or pulmonary infections. Abscess also can occur from ascending urinary tract infection. The most common mechanism for gram-negative bacterial abscess to develop is the rupture of a corticomedullary abscess, while the most common mechanism for the development of a staphylococcal infection is the rupture of a renal cortical abscess. This finding frequently is observed in association with a previous renal operation such as a partial nephrectomy or nephrolithiasis or, most commonly, as a complication of diabetes mellitus (60-90%). Perforation of a ureter or a calyceal fornix may rarely result in perinephric abscess formation. Occasionally, a perinephric abscess may result from the spread of infection from extraperitoneal sites, such as in retroperitoneal appendicitis, diverticulitis, pancreatitis, and pelvic inflammatory conditions. Patients with polycystic renal disease who undergo hemodialysis may be particularly susceptible to developing perinephric abscess (62% of cases). Predisposing factors for perinephric abscess include neurogenic bladder, vesicoureteral reflux, bladder outlet obstruction, renal papillary necrosis, obstructing calculus, genitourinary tuberculosis, trauma (eg, renal biopsy, urinary instrumentation, urologic surgery), immunosuppression, and intravenous drug abuse. When a perinephric infection ruptures through the Gerota fascia into the pararenal space, it leads to the formation of a paranephric abscess. Paranephric abscesses also may be caused by infectious disorders of the intestine, pancreas, liver, gall bladder, prostate, and pleural cavity, and they may be caused by osteomyelitis of adjacent ribs or vertebrae. Sometimes with a superimposed infection, a perirenal hematoma can turn into a perinephric abscess. Clinical: Because of nonspecific findings, in many cases, diagnosing a perinephric abscess can be difficult. In fact, one third of cases may not be diagnosed until autopsy. Typically, patients present with a history of skin infections or urinary tract infections. An infection is followed in 1-2 weeks by fever and unilateral flank pain. However, this is an uncommon presentation. Typically, the onset of symptoms is quite insidious, and 58% of patients have symptoms for more than 14 days. Presenting symptoms often are nonspecific. Only occasionally, a patient presents with a syndrome suggestive of acute pyelonephritis, with fever and abdominal and flank pain (usually unilateral). One distinguishing feature to note is that most patients with uncomplicated pyelonephritis are symptomatic for less than 5 days before hospitalization, whereas most patients with perinephric abscesses are symptomatic for more than 5 days. The most common symptoms are fever (90%), flank or abdominal pain (40-50%), chills (40%), dysuria (40%), weight loss, lethargy, and gastrointestinal symptoms (25%). Pleuritic pain may occur due to diaphragmatic irritation. If the abscess is pressing the adjacent nerves, the referred pain may be felt in the groin, thighs, or knees. Physical findings include flank or costovertebral tenderness. When abdominal tenderness is present (60%), it may create confusion in the diagnosis. Patients may present with rigidity and fullness. A flank mass is palpable if the abscess is large or is present in the inferior pole of the kidney space (9-47%). A renal malignancy must be ruled out in these patients by performing appropriate radiographic studies (eg, CT scan, MRI). Splinting may be present, with resultant scoliosis. Patients may have pain upon bending toward the contralateral side, upon active flexion of the ipsilateral thigh against resistance, and upon extension of the thigh while walking. Diabetes is present in 36-42% of patients, and renal or ureteric calculi are present in 19-50% of patients. Consider the diagnosis of perinephric abscess in patients with unilateral flank pain and fever, no response to treatment for acute pyelonephritis, pyrexia of unknown origin, unexplained peritonitis, pelvic abscess, and empyema.
Promptly treat all perinephric abscesses. Failure to treat can result in severe morbidity or even death. Certain conditions such as renal cortical abscess or enteric fistulas may require immediate surgical intervention (see Surgical therapy).
Relevant Anatomy: Knowledge of retroperitoneal structures is highly important to understand the development of perinephric abscesses. Anterior and posterior layers of renal fascia divide the retroperitoneum in 3 extraperitoneal spaces. The first, the anterior paranephric space, extends from the posterior peritoneum to the anterior renal fascia (Gerota). The second, the perinephric space, lies between 2 layers of the renal fascia. The third, the posterior paranephric space, extends from the posterior renal fascia to the fascia that lies anterior to the psoas and quadratus lumborum muscles. The renal fascia (Gerota) surrounds the kidney and adrenal gland. Perinephric fat is present between the renal capsule and this fascia. The perinephric space also contains some blood vessels and lymphatics, which facilitate the spread of infection. The 2 layers join above the adrenal glands and are attached to the diaphragmatic fascia. They join laterally to form the lateroconal fascia that is present posterior to the colon. The anterior fascia of Zuckerkandl extends anterolaterally and then blends with the parietal peritoneum. Posteriorly, the Gerota fascia joins the quadratus lumborum fascia medially, while the anterior fascia joins the root of the mesentery and lies behind the pancreas and the duodenum. The perinephric space becomes cone-shaped as it narrows inferiorly and medially and then joins with the iliac fascia. The inferomedial angle of the space is the weakest point, accounting for the extension of fluid collection across the midline and into the pelvis. Contraindications: The only contraindication to treatment is bleeding dyscrasias. Correct this condition prior to percutaneous drainage. A relative contraindication is patients who are at increased anesthetic risk who require nephrectomy for treatment. Optimize these individual medical conditions prior to surgery. |
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Lab Studies:
Imaging Studies:
Medical therapy: The mainstay of treatment for perinephric abscess is drainage. Antibiotics mainly are used as an adjunct to percutaneous drainage because they help to control sepsis and prevent the spread of infection. When kidneys are not functioning or are severely infected, nephrectomy (open or laparoscopic) is the classic treatment for perinephric abscesses. Percutaneous drainage is relatively contraindicated in large abscess cavities that are filled with a thick purulent fluid. However, attempt percutaneous drainage as the first line of therapy in these patients. These individuals require close observation for signs of sepsis, and use serial CT scans to confirm that the perinephric abscess cavity is draining. Direct empiric antibiotics against common gram-negative organisms and S aureus. An antistaphylococcal beta-lactam agent (eg, nafcillin, cefazolin) and an aminoglycoside (eg, gentamicin) are appropriate choices for the initial treatment. After the culture report, the antibiotics can be adjusted accordingly. If the report is positive for pseudomonads, an antipseudomonal beta-lactam (eg, mezlocillin, ceftazidime) can be started. For infection with enterococci, ampicillin and gentamicin are the treatment of choice. Isoniazid, rifampin, and ethambutol are indicated for M tuberculosis, and fungal infections require amphotericin B. Percutaneous drainage diagnostic aspiration under ultrasound guidance carries minimal morbidity. Therefore, a trial of percutaneous drainage should be the initial modality of treatment for perinephric abscess. This approach is contraindicated in the setting of bleeding diathesis and when a hydatid cyst may be present. Administer broad-spectrum intravenous antibiotics before the procedure. Under local anesthesia, a 22-gauge Chiba needle is passed percutaneously into the abscess cavity under ultrasound or CT-scan guidance. Approaching the abscess below the level of the 12th rib is important to prevent pneumothorax and empyema. One also should avoid the peritoneal cavity by choosing the access point medial to the posterior axillary line. Once the abscess is located with a thin needle, aspiration is attempted using an 18-gauge needle. Fluid is drained from the abscess, and a sample is sent for aerobic, anaerobic, and fungal cultures. At this time, a catheter (eg, 10F locking-loop catheter or a 12F or 14F double-lumen sump drain such as a Van Sonnenberg or Ring-McLean catheter) is placed into the abscess cavity. The double-lumen catheter helps decrease clogging and can be used for irrigation with isotonic sodium chloride solution or antibiotic solution. If indicated, a separate tube is placed to drain the collecting system (ie, nephrostomy tube). This is needed if the patient has renal obstruction from a stone or stricture. Advantages of percutaneous drainage include the following:
Similar to the results for other types of intra-abdominal abscesses, percutaneous drainage of the retroperitoneal abscess has a success rate of 76-90%. The success rate is higher for single unilocular abscesses than for multilocular abscesses (82% vs 45%). Poor results are seen in the following situations:
Surgical therapy: Certain conditions such as renal cortical abscess or enteric fistulas may require immediate surgical intervention. After the perinephric abscess has been incised and drained through a retroperitoneal approach, search for the underlying problem.
Nephrectomy is reserved for the following situations:
Follow-up care: After approximately 5-7 days of percutaneous drainage, drainage from the abscess stops. However, if the amount of drainage is small in the beginning and then begins to increase or becomes clear, suspect a urinary fistula. Workup should include IVP and/or retrograde pyelogram to rule out the presence of a urinary fistula. If such a fistula is present, urinary diversion is required in the form of an indwelling ureteral stent or percutaneous nephrostomy tube.
Prior to removal of the drainage tube, obtain an ultrasound, CT scan, or a contrast study. If the cavity has substantially decreased, the catheter can be removed.
For a persistent large cavity, sclerosing therapy is recommended. Generally, tetracycline or 95% alcohol is used for this purpose. Tetracycline is instilled into the cavity, and the tube is clamped for 15 minutes and then opened for drainage. The process is repeated on a weekly basis until the cavity is almost obliterated. The tube is removed at this time.
A potential concern is that if small cavities persist and remain colonized, sclerosing therapy may be ineffective. The mere presence of a large cavity does not necessarily mandate sclerosing therapy. Provided that the underlying cause of the perinephric abscess is treated, most cavities eventually self-obliterate.
If percutaneous drainage is not effective in improving the patient's clinical situation, open surgical debridement with placement of large drains may be necessary
Appropriate oral antibiotics are given throughout the drainage/sclerosant period and for 1-3 weeks after the drainage tube is withdrawn.
Follow-up examinations, with urine cultures, ultrasound, or CT scans, are performed at 1-month and 3-month intervals to rule out recurrent infection.
Recurrence after percutaneous drainage is relatively rare (1-4%). Surgical intervention is needed in 3-22% of cases.
If the fluid is thick and drains poorly or if the cavity is multiloculated, an open or laparoscopic operation is recommended for drainage and debridement.
For excellent patient education resources, visit eMedicine's Infections Center and Kidneys and Urinary System Center. Also, see eMedicine's patient education articles Urinary Tract Infections, Abscess, and Antibiotics.
Various complications can occur, including the following:
A nephrocolonic fistula occurs if the abscess erodes into the adjacent part of the colon. The patient may present with bloody stool, diarrhea, passing of urine per rectum, and passing of fecal contents into the urine. If this fistula opens on to the skin, urine and feces are discharged through the nephrocolocutaneous fistula.
Perinephric abscess is a life-threatening entity. The diagnosis is difficult to make from a patient's history and physical examination findings alone because the findings are nonspecific. The mortality rate for perinephric abscesses can be as high as 56%. This rate partly is due to long delays in making the diagnosis. Even with modern surgical therapy, the mortality rate is 8-22% and significant morbidity occurs in 35% of patients. The mortality rate is higher in the following situations:
Recent studies indicate that a marked reduction in mortality rates has occurred with early diagnosis, immediate drainage, and antibiotic therapy. Criteria for successful treatment include the presence of negative cultures and the resolution of any underlying obstruction.
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