A perinephric abscess is a collection of suppurative material in the renal parenchyma or perinephric space, with a presentation that is insidious (patients may not present until more than 2 weeks after onset). This abscess formation occurs secondary to urinary tract obstruction and/or hematogenous spread from infection sites.[1] 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.
All perinephric abscesses should be promptly treated; failure to treat can result in severe morbidity or even death. Treatment is usually with percutaneous drainage and adjunctive antibiotics. Open surgical debridement with placement of large drains may be necessary if percutaneous drainage is ineffective; nephrectomy may be indicated in some cases (eg, if the kidney is nonfunctional or severely infected). Certain conditions, such as renal cortical abscess or enteric fistulas, may require immediate surgical intervention (see Treatment).[2]
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 the following 3 extraperitoneal spaces:
The anterior paranephric space extends from the posterior peritoneum to the anterior renal fascia (Gerota).
The perinephric space lies between 2 layers of the renal fascia.
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 (Gerota) fascia surrounds the kidney and adrenal gland. Perinephric fat is present between the renal capsule and this fascia. The perinephric space also contains 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, posterior to the colon, to form the lateroconal fascia. 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.
Zuckerkandl described the posterior renal fascia in 1883, but did not recognize the presence of the anterior renal fascia. In 1895, Gerota documented the presence of the anterior renal fascia and assigned Zuckerkandl's name to the posterior renal fascia. Thus, the terms Zuckerkandl fascia and posterior renal fascia are synonymous, as are Gerota fascia and anterior renal fascia.[3]
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.
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,[5] 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.
Perinephric abscesses may occur as a complication of urinary tract infections. Escherichia coli, Proteus species, and Staphylococcus aureus are the usual pathogens. Perinephric abscesses due to S aureus are usually secondary to hematogenous seeding of infection.[6] The use of antibiotics for skin and wound infections 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 species of gram-negative bacteria that can cause this infection include the following:
Klebsiella
Enterobacter
Pseudomonas
Serratia
Citrobacter
Although C koseri has been isolated with increased frequency from the urine of hospitalized patients, fewer than 6 reported cases of renal or perinephric abscess have been attributed to this opportunistic infection.[7] Risk factors for this pathogen include diabetes, the presence of an indwelling Foley catheter, and a history of genitourinary instrumentation or obstruction.[8]
Occasionally, perinephric abscess may be caused by enterococci. Streptococcus infection (Group B, S pneumoniae) has been reported.[5, 9] Anaerobes such as Clostridium, Bacteroides, and Actinomyces can be present in as many as 25% of cases.
Perinephric abscess secondary to Candida infection usually occurs in patients with diabetes mellitus. Predisposing factors include surgery (including kidney transplantation[10] ) and prolonged antibiotic therapy.
Splenectomy may increase the risk of perinephric abscess. A population-based retrospective cohort study from Taiwan found that the adjusted hazard ratio (HR) of renal and perinephric abscesses was 2.24 for the splenectomy group compared with the non-splenectomy group. The adjusted HR was markedly increased to 7.69 for splenectomized persons with diabetes mellitus.[11]
Urinary tract abnormalities that predispose to the development of perinephric abscess include the following[12] :
The incidence of perinephric abscesses ranges from 1-10 cases for every 10,000 hospital admissions. Men and women are affected with equal frequency. Patients with diabetes mellitus account for one-third of all perinephric abscess cases.[13]
Perinephric abscess is a life-threatening entity, with a mortality rate of up to 56%. Even with modern surgical therapy, the mortality rate is 8-22% and significant morbidity occurs in 35% of patients. The high morbidity and mortality rates are partly due to long delays in diagnosis and the comorbid conditions in these patients. Diagnosis may be delayed because the findings on history and physical examination are typically nonspecific.
Factors associated with higher mortality rate include the following:
More severe illness and sepsis
Urinary tract obstruction
Lethargy
Higher temperature (> 104°F)
The presence of additional underlying diseases and related conditions, such as diabetic ketoacidosis
Obscure presentation
White blood cell count greater than 25,000 cells/μL
High blood urea nitrogen (BUN) level
Positive blood cultures
Diagnostic delay
Previous urinary tract infections
Early diagnosis, immediate drainage, and antibiotic therapy can markedly reduce mortality rates. Criteria for successful treatment include the presence of negative cultures and the resolution of any underlying obstruction.
Because of nonspecific findings in many cases, diagnosing a perinephric abscess can be difficult. Typically, patients present with a history of skin infection or urinary tract infection (UTI). Such infections may be followed in 1-2 weeks by fever and unilateral flank pain. However, this is an uncommon presentation.
The onset of symptoms is often insidious, and 58% of patients have had symptoms for more than 14 days.
Presenting symptoms are often nonspecific. Only occasionally does a patient present 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 five days before hospitalization, whereas most patients with perinephric abscesses are symptomatic for more than five 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 on the adjacent nerves, 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, computed tomography, magnetic resonance imaging).
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. Features that suggest the possible diagnosis of perinephric abscess include the following:
Unilateral flank pain and fever
No response to treatment for acute pyelonephritis
Pyrexia of unknown origin
Unexplained peritonitis, pelvic abscess, and empyema
Computed tomography (CT) is the preferred technique for diagnosing perinephric abscesses. Renal ultrasonography is used for screening. 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.
View Image
Diagnostic CT prior to intervention.
View Image
CT post percutaneous drainage.
CT findings will include a low-density and defined fluid collection, typically with Hounsfield Units between 0 and +40. The collection itself will not enhance; however, the abscess wall may enhance. In patients unable to receive an iodinated contrast scan, a gallium-based MRI scan serves as an alternative option. [15]
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.
View Image
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 small study, ultrasonographic results were falsely negative in 36% of cases when compared with CT scanning.[16] 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 kidney 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.
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 Staphylococcus 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 Mycoplasma tuberculosis, and fungal infections require amphotericin B. If methicillin-resistant Staphylococcus aureus (MRSA) is present, daptomycin or vancomycin can be administered.[17]
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.
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
If percutaneous drainage is not effective in improving the patient's clinical situation, open surgical debridement with placement of large drains may be necessary.
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.
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.
Appropriate oral antibiotics are given throughout the drainage/sclerosant period and for 1-3 weeks after the drainage tube is withdrawn.
To rule out recurrent infection, follow-up examinations, with urine cultures, ultrasonography, or CT scanning, are performed at 1-month and 3-month intervals.
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. However, novel approaches to percutaneous drainage include larger-bore pigtail catheter placement under ultrasound guidance for larger and more loculated collections as a safe alternative to open operation.[18, 19]
Certain conditions, such as renal cortical abscesses, enteric fistulas, or multilocular abscesses, may require immediate surgical intervention.[20] 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
Chronic recurrent infection
Poor function of the affected kidney, with appropriate contralateral function
Complications of perinephric abscess include 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.
A case of Fournier gangrene following renal transplant has been attributed to a perinephric abscess.[21]
Edward David Kim, MD, FACS, Professor of Urology, Department of Urology, University of Tennessee Graduate School of Medicine; Consulting Staff, University of Tennessee Medical Center
Disclosure: Nothing to disclose.
Coauthor(s)
Abhilash N Moolupuri, MD, Resident Physician, Department of Urology, University of Tennessee Graduate School of Medicine
Disclosure: Nothing to disclose.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Chief Editor
Bradley Fields Schwartz, DO, FACS, Professor of Urology, Frank and Linda Vala Endowed Chair of Urology, Director, Center for Laparoscopy and Endourology, Department of Surgery, Division of Urology, Southern Illinois University School of Medicine
Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Endourological Society Board of Directors<br/>Serve(d) as a speaker or a member of a speakers bureau for: Cook Medical<br/>Received research grant from: Cook Medical.
Additional Contributors
Daniel B Rukstalis, MD, Professor of Urology, Wake Forest Baptist Health System, Wake Forest University School of Medicine
Disclosure: Nothing to disclose.
Jared Moss, MD, Resident Physician, Division of Urology, University of Tennessee Graduate School of Medicine
Schaeffer AJ. Infections of the urinary tract. PC Walsh, AB Retik, et al. Campbell's Urology. 8th Edition. Philadeelphia: W.B. Sanders Company; 515-602.
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