Perinephric Abscess 

Updated: May 02, 2016
Author: Edward David Kim, MD, FACS; Chief Editor: Bradley Fields Schwartz, DO, FACS 

Overview

Background

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 increases the risk of morbidity and mortality. Diagnosis of a perinephric abscess should be considered in any patient with fever and abdominal or flank pain.

The increased use of CT scanning has allowed for earlier and accurate diagnoses of this condition, 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 tract obstruction and/or hematogenous spread from infection sites.

Epidemiology

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. Patients with diabetes account for one third of all perinephric abscess cases.[1]

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 include Klebsiella, Enterobacter, Pseudomonas, Serratia, and Citrobacterspecies.

Occasionally, the infection can occur from enterococci infection. One case caused by Streptococcus pneumoniae infection has been reported.[2] 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[3] ) 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.[4] Approximately 30% of cases are attributed to hematogenous dissemination of organisms from sites of infection such as wound infection, furuncles, or pulmonary infections. Abscesses can also be caused by 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 results from the spread of infection from extraperitoneal sites, such as in retroperitoneal appendicitis, diverticulitis, pancreatitis, and pelvic inflammatory conditions. In some instances, perinephric abscess is caused by bowel perforation, Crohn disease, or osteomyelitis from the spine.

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,[2] 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 may also 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 progress to a perinephric abscess.

Presentation

Because of nonspecific findings, in many cases, diagnosing a perinephric abscess can be difficult. Typically, patients present with a history of skin infections or urinary tract infections. An infection may be followed in 1-2 weeks by fever and unilateral flank pain. However, this is an uncommon presentation.

Typically, the onset of symptoms is insidious, and 58% of patients have symptoms for more than 14 days.

Presenting symptoms are often 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 include fever (66-90%), 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 complicate the diagnosis. Patients may present with rigidity and fullness. A flank mass is palpable if the abscess is large or located in the inferior pole of the kidney space (9-47%). A renal malignancy must be ruled out in these patients with appropriate radiographic studies (eg, CT scanning, MRI). Splinting may be present, with resultant scoliosis. Patients may experience pain upon bending toward the contralateral side, upon active flexion of the ipsilateral thigh against resistance, and upon extension of the thigh while walking. 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.

Indications

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).[5]

Relevant Anatomy

Knowledge of the retroperitoneal structures is vital in understanding the development of perinephric abscesses.

Anterior and posterior layers of renal fascia divide the retroperitoneum into 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 of a perinephric abscess 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.

 

Workup

Laboratory Studies

Blood study results in perinephric abscess include the following:

  • A CBC count usually reveals leukocytosis with a shift to the left

  • A WBC count that exceeds 15,000 cells/μL is uncommon

  • Anemia occurs in 42% of cases

  • The erythrocyte sedimentation rate is elevated

  • Azotemia may be present

  • Blood culture identifies the pathogen in fewer than 50% of cases

Urine study results in perinephric abscess include the following:

  • Urinalysis shows pyuria in 75% of patients

  • Proteinuria can be a common finding.

  • Hematuria occurs in 30% of patients

  • Urine cultures are positive in 43-75% of cases[6]

Imaging Studies

Computed tomography (CT) and renal ultrasonography have become the preferred techniques for diagnosing perinephric abscesses. In approximately 50% of cases, chest radiography can show a pleural effusion, elevated ipsilateral hemidiaphragm, atelectasis, and a lower-lobe infiltrate.

Computed tomography

CT scanning is the diagnostic modality of choice because it is more sensitive and accurate in diagnosing an intra-abdominal abscess (90%) than ultrasonography (see image below). CT scanning is also more effective in defining the precise location, size, degree, and extent of the loculation in relation to other retroperitoneal structures.

Diagnostic CT prior to intervention. Diagnostic CT prior to intervention.
CT post percutaneous drainage. CT post percutaneous drainage.

The typical appearance of a perinephric abscess on a CT scan is that of a soft-tissue mass (20 Hounsfield unit) with a thick wall that may enhance after introduction of intravenous contrast material (ie, the Rind sign). Other findings on CT scans may include the following:

  • Renal enlargement
  • Focal parenchymal decreased attenuation; fluid, gas, or both in and around the kidneys
  • Focal thickening of the Gerota fascia
  • Obliteration of adjacent tissue planes

Ultrasonography

Ultrasonography can demonstrate the fluid collections that may be poorly visualized with radiography. Ultrasonography is used as a screening tool to assess for obstructive uropathy (when suspected), to exclude another intra-abdominal or retroperitoneal process, and to exclude suppurative renal complications. Findings on ultrasonography depend on the homogeneity of the abscess contents. Ultrasonography is able to reveal abscesses 2 cm or larger in diameter.

Findings may include the following:

  • A hypoechoic or a nearly anechoic mass displacing the kidney
  • A fluid debris level
  • A thick irregular wall
  • The image below depicts an anechoic fluid collection in perinephric abscess.
Sonogram showing large anechoic fluid collection i Sonogram showing large anechoic fluid collection in perinephric abscess (arrow).

Findings may also include increased echogenicity if gas bubbles are present in the cavity and an echogenic collection that tends to blend with normally echogenic fat within the Gerota fascia.

Advantages of ultrasonography include its noninvasiveness, lack of radiation, portability, relative accessibility, capability to be used as an initial screening tool, and its capability to be helpful in carrying out percutaneous drainage.

In one study, ultrasonographic results were falsely negative in 36% of cases when compared with CT scanning. Notably, the findings mentioned are not specific because they can also be seen in urinoma, hematoma, and lymphocele.

Radiography

A plain abdominal film may show different abnormalities; however, film findings can be normal in 40% of patients. When radiography results are positive, the findings include the following:

  • The psoas margin is absent; however, findings may be falsely positive bilaterally in 3% of healthy patients and falsely positive unilaterally in another 10% of cases
  • Renal masses are apparent
  • Absent renal outlines with increased density in the region of the kidney are seen in 50% of cases
  • Displacement and rotation of the kidney can occur from collection of fluid in certain portions of the perinephric space
  • Radiopaque renal calculi are present
  • Retroperitoneal gas may be due to gas-forming bacteria such as E coli, Aerobacter aerogenes, and, rarely, Clostridium species
  • Gas may have a mottled appearance, or it may surround the kidney completely
  • Scoliosis with a concavity toward the abscess occurs in approximately 50% of cases
  • Displaced bowel gas may be due to mass effect from a large abscess on the adjacent duodenum, stomach, or colon
  • Infiltration of the flank stripe can occur from widening of the extraperitoneal flank fat

Intravenous pyelography

Intravenous pyelography (IVP) results are abnormal in 80% of cases. However, this study is being performed less frequently. When results are positive, the abnormalities include the following:

  • A kidney with little or no function is present in 64% of patients

  • Calicectasis or calyceal stretching occurs in 39% of patients

  • Calculi are present in 14% of patients

  • Renal displacement occurs in 4% of patients

  • Renal fascia may be opacified, thickened, and displaced

  • Rarely, extravasation of contrast material into the perinephric space can be observed

Angiography

Renal arteriography is rarely necessary because of the more commonly available CT angiography and MRI angiography. Findings include the following:

  • Vasoconstriction (as opposed to vasodilatation), which is a unique response to inflammation, may be seen
  • Persistent arterial filling (staining) after the kidney has reached the nephrotomographic phase; however, distinguishing the abscess from hypovascular necrotic neoplasms may be difficult
  • Increased number and size of the perforating arteries extending from the kidney
  • Tissue blush
  • Displacement of the renal capsular artery away from the kidney

None of the above angiographic abnormalities is pathognomonic.

Mobility tests

More specific information is obtained from the assessment of renal mobility using fluoroscopy or obtaining inspiration-expiration films. This mobility test provides a specificity rate of 85%. Normal kidneys move 2-6 cm with respiration; however, a kidney with perinephric abscess is fixed to the surrounding tissues and does not move during respiration (Mathe sign).

Magnetic resonance imaging

On MRI, thick pus has high signal intensity on T1 images. Abscesses are more visible on T1 images, but if those that extend into adjacent structures are more visible on T2 images. T2-weighted images show the central portion of abscess as high signal intensity, and the wall has medium-to-low intensity.

Advantages of MRI include no radiation exposure, better contrast sensitivity, the fact that it is not affected by metal clips or bone, better delineation of underlying soft tissues such as psoas muscle, and its usefulness in patients with allergy to contrast or renal insufficiency. Disadvantages include the long imaging time, insensitivity to calcifications and small gas collections, limited use in some patients with pacemakers, contraindication with intracranial aneurysm clips, and expense.

Radionuclide imaging

In radionuclide imaging, gallium citrate (Ga-67) is rarely especially useful when the local anatomy is distorted because of congenital anomalies, previous surgery, polycystic kidney disease, and chronic pyelonephritis. This scan has a true positive rate of 90% and a true negative rate higher than 90%.

Disadvantages include the possibility of obtaining a false-positive result in conditions such as pyelonephritis, acute tubular necrosis, vasculitis, and neoplasms; high radiation exposure; and a delay of as long as 72 hours before imaging can be performed.

A WBC scan labeled with indium (In-111) is more sensitive, and it may be helpful for diagnosis.

 

Treatment

Medical Therapy

The mainstay of treatment for perinephric abscess is drainage. Antibiotics are mainly used as an adjunct to percutaneous drainage because they help to control sepsis and to 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 scanning 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 ultrasonographic 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 ultrasonographic or CT 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:

  • Earlier diagnosis and treatment

  • Avoidance of general anesthesia and surgery

  • Low cost

  • Greater acceptance by the patient

  • Easier nursing care

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:

  • Presence of fungal infection

  • Calcification of the wall of the mass

  • Calcified debris within the mass

  • Thick purulent drainage

  • Multiloculated cavity

  • Emphysematous changes in the kidney

  • Markedly diseased nonfunctioning kidney

  • Underlying diseases such as calculi and diabetes

  • Infected hematoma

Surgical Therapy

Certain conditions, such as renal cortical abscess, enteric fistulas, or multilocular abscesses, may require immediate surgical intervention.[7] 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:

  • Emphysematous pyelonephritis

  • Diffusely damaged parenchyma

  • Older patients who are septic and require urgent intervention

  • Intractable cases

Follow-up

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 pyelography 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, perform ultrasonography, CT scanning, 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, ultrasonography, or CT scanning, 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 eMedicineHealth's Infections Center. Also, see eMedicineHealth's patient education articles Urinary Tract Infections, Abscess, and Antibiotics.

Complications

Various complications can occur, including the following:

  • Bleeding

  • Flank abscess

  • Fistula formation to stomach, small bowel, duodenum, lung

  • Subphrenic abscess

  • Empyema

  • Pneumonia

  • Atelectasis

  • Sepsis

  • Possible rupture into peritoneum

  • Possible perforation through diaphragm

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.

Outcome and Prognosis

Perinephric abscess is a life-threatening entity. The diagnosis is difficult based on a patient's history and physical examination findings alone because the findings are nonspecific. Perinephric abscesses carry a mortality rate of up to 56%. This rate partly is due to long delays in diagnosis and the comorbid conditions. 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:

  • Patients who are more ill and have sepsis

  • Urinary tract obstruction

  • Lethargy

  • Higher temperature (>104°F)

  • The presence of more underlying diseases such as diabetic ketoacidosis

  • Obscure presentation

  • WBC count greater than 25,000 cells/μL

  • High BUN

  • Positive blood cultures

  • Diagnostic delay

  • Previous urinary tract infections

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.