Jessica H. Hannick, MD
Ahmer V. Farooq, DO
BASICS
DESCRIPTION
• A retroperitoneal abscess is an infectious process that involves the retroperitoneum.
• The retroperitoneum spans anteroposteriorly from the peritoneum to posterior pariet al wall of the abdominal cavity and craniocaudally from the diaphragm to the pelvic floor.
• Most common source of infection is from renal diseases.
EPIDEMIOLOGY
Incidence
Reported highest incidence in 3rd–6th decades.
Prevalence
N/A
RISK FACTORS
• Appendicitis
• Diabetes
• Diverticulitis
• Existing osteomyelitis or epidural infection
• GU tract obstruction
• Immunosuppression
• Inflammatory bowel disease (Crohn’s disease)
• Malignancy
• Osteomyelitis
• Pyelonephritis
• Recent instrumentation or surgery of the GU or GI tract
• Systemic infection (ie, hematogenous spread from remote infection)
• Trauma
• Tuberculosis
PATHOPHYSIOLOGY
• Retroperitoneal abscess is an infectious process that can be found in 1 of 4 retroperitoneal compartments (1):
– Anterior retroperitoneum:
Esophagus, duodenum, pancreas, bile duct, portal and splenic veins, appendix, ascending/descending colon, rectosigmoid
– Posterior retroperitoneum (aka perinephric/perirenal):
Kidneys, ureters, gonadal vessels, aorta, inferior vena cava, lymphatics
See “Renal and Perirenal Abscess”
– Retrofascial (aka iliopsoas):
12th rib, spine, paraspinous muscles
– Pelvic retroperitoneal:
Prevesical, retrovesical, presacral, perirectal spaces
• Primary infection if spread is hematogenous (75–90% Staphylococcus aureus)
• Secondary infection if spread is from infected adjacent organs (78% enteric bacteria).
• Most common source is from renal diseases accounting for 47% of retroperitoneal abscesses.
• Infection seeds a contained space in retroperitoneum:
– Depending on the source, anaerobic and aerobic organisms may be present.
– Usual source is normal flora from a nearby organ site (eg, GI, GU, female reproductive tract).
– Multimicrobial infections are common.
– Malignancy frequently violates fascial barriers, whereas abscesses tend to be contained by the fascia.
– Hypoxia and lack of appropriate blood supply limit effective immune response.
– If untreated, bacteremia, followed by shock ensues.
• TB and Staphylococcus (skin source) were previously major pathogens, but are less common today.
• Proteus and Escherichia coli are the most commonly cultured bacteria in retroperitoneal abscesses.
• Common pathogens (aerobic and anaerobic) (2,3):
– Enterobacteriaceae:
E. coli
Klebsiella pneumonia
Proteus sp.
Pseudomonas aeruginosa
– Anaerobes:
Peptostreptococcus sp.
Bacteroides fragilis
Prevotella sp.
Clostridium sp.
– Enterococcus sp.
– Streptococcus sp.
– S. aureus
• Site-specific pathogens:
– Pancreatic abscess:
S. aureus
K. pneumoniae
P. aeruginosa
– Pelvic retroperitoneal:
Neisseria gonorrhoeae
Streptococcus B
– Anterior retroperitoneal:
Clostridium sp.
Fusobacterium nucleatum
ASSOCIATED CONDITIONS
• Diabetes, liver disease, renal insufficiency, immunosuppression, retroperitoneal hematoma
• GU specific: Urinary tract infection (UTI), urolithiasis, instrumentation/surgery, malignancy
• GI specific: Malignancy, surgery, pancreatic pathology
GENERAL PREVENTION
Perioperative antibiotic prophylaxis
DIAGNOSIS
HISTORY
• Abdominal or flank pain (60–75%)
• Sweats, fever, and chills (30–90%)
• Malaise (10–22%)
• Nausea/vomiting
• Altered bowel habits
• Dysuria
• Weight loss (12%)
• Duration of symptoms is typically longer than 1 wk
• Recent instrumentation/surgery/trauma
• Recent treatment for UTI
• History of urolithiasis, inflammatory bowel disease, pancreatitis, diverticulitis, appendicitis, osteomyelitis, malignancy, TB
• Medical comorbidities: Diabetes, renal insufficiency, immunosuppression (ie, HIV)
PHYSICAL EXAM
• General vital signs:
– Fever
– Tachycardia
– Tachypnea
• Unlike peritoneal cavity, retroperitoneum is relatively concealed on exam.
• Assess for:
– Tenderness: Usually localized, dull, and mild
– Costovertebral angle tenderness
– Palpable flank/abdominal mass
– Lower abdominal, groin, and/or upper thigh referred pain due to irritation of retroperitoneal nerves
– Psoas sign: Increased pain when flexing patient’s thigh against examiner’s hand; suggests involvement of psoas muscle
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Lab findings often nonspecific (ie, elevated ESR)
• Obtain CBC (leukocytosis)
• BMP: Serum glucose often elevated
• Urinalysis
– Approximately 30% will have microscopic hematuria.
– Pyuria is also very common.
• Urine/blood/abscess cultures
Imaging
• Cross-sectional CT or MRI is most helpful:
– CT (100% sensitivity, 77% specificity):
Low-density mass in retroperitoneum with surrounding inflammation
Gas may be present in approximately 33% of cases
Evaluates surrounding organs (ie, possible sources)
• MRI:
– Thick purulent collections have high-intensity signal on T1-weighted images
– Edema in surrounding fat seen as high signal on T2-weighted images
– High soft tissue contrast resolution sensitive for detecting psoas muscle pathology and intervertebral disc involvement
– May not show calcifications or gas collections
• US: Can reveal gas/fluid collections
• KUB: May show psoas shadow, loss of renal outline, displacement of organs, gas, or urolithiasis
• Gallium67 citrate and indium111 chloride scanning can be helpful:
– False positives: Pyelonephritis, acute tubular necrosis, vasculitis, and neoplasms
• Chest x-ray may show elevation of hemidiaphragm, pleural effusions, secondary pneumonia
Diagnostic Procedures/Surgery
• CT, MRI, or US-guided aspiration and drainage of abscess cavity
• Specimens must be sent for both aerobic and anaerobic cultures
• Consider sending for AFB culture
Pathologic Findings
Coagulation necrosis
DIFFERENTIAL DIAGNOSIS
• Malignancy
• Necrotizing fasciitis
• Osteomyelitis
• Pancreatitis
• Perforated viscus (ie, duodenal ulcer)
• Perinephric aneurysm/pseudoaneurysm
• Perinephric/perirenal abscess
• Psoas abscess
• Pyelonephritis
• Ruptured aortic aneurysm
• TB
• Trauma/retroperitoneal hematoma
• Urinoma
TREATMENT
GENERAL MEASURES
• Supportive care
• DVT prophylaxis
MEDICATION
First Line
• Broad-spectrum antibiotics to empirically cover most likely pathogens (ampicillin, gentamicin, and metronidazole) (4)
– Refine antibiotic coverage based on culture results
– Tailor duration of treatment to clinical progress
Second Line
N/A
SURGERY/OTHER PROCEDURES
• Early percutaneous drainage (5)
– Essential in lesions >3 cm
– May consider antibiotics only in abscesses <3 cm
• Surgical drainage must be considered if:
– Safe percutaneous drainage not possible
– Percutaneous drainage has failed
– Multiple abscesses
– Multiloculated abscesses
– Purulent material too thick to be drained
– If patient is persistently febrile after 48–72 hr of appropriate antibiotics
– If primary cause must be addressed surgically (ie, xanthogranulomatous pyelonephritis (XGP), malignancy, urolithiasis)
• Surgical approach should be retroperitoneal unless pancreatic pathology is present:
– Obtain cultures
– Irrigate abscess cavity aggressively
– Use drains liberally
ADDITIONAL TREATMENT
Radiation Therapy
No role
Additional Therapies
N/A
Complementary & Alternative Therapies
N/A
ONGOING CARE
PROGNOSIS
• Mortality is considerable (5–50%) despite modern management that combines antibiotics, drainage, and intensive care support.
• High success with antibiotics and percutaneous drainage (>80%):
• Only 1–4% recurrence with percutaneous drainage
• If abscess is not drained and only antibiotics are used, mortality approaches 100%
COMPLICATIONS
• Abscess crossing the midline to opposite side or tracking into the ipsilateral thigh
• DVT
• GI bleed
• Organ failure
• Pneumonia
• Secondary infections: Osteomyelitis, involvement of psoas muscle, fistulization to the skin
FOLLOW-UP
Patient Monitoring
• Reimaging necessary
– CT or MRI (MRI avoids radiation)
– Timing depends on clinical progress
• Drains:
– Must be monitored carefully and irrigated appropriately
• Can be removed when:
– Patient is clinically improved
– Drainage stops (<10 mL/d) or becomes serous
– Abscess cavity involution is documented on imaging
PATIENT RESOURCES
N/A
REFERENCES
1. Solomkin JS. Peritonitis, pancreatitis and intra-abdominal abscesses. In: Cohen J, Powderly WG, eds. Cohen & Powderly: Infectious Diseases. 2nd ed. Philadelphia, PA: Mosby; 2004:517–527.
2. Anaya DA, Dellinger EP. Surgical infections and choice of antibiotics. In: Townsend CM Jr, Beauchamp RD, Evers M, et al., eds. Sabiston Textbook of Surgery. 18th ed. Philadelphia, PA: Saunders Elsevier; 2008.
3. Brook I, Frazier EH. Aerobic and anaerobic microbiology of retroperitoneal abscesses. Clin Infect Dis. 1998;26:938–941.
4. Crepps JT, Welch JP, Orlando R 3rd. Management and outcome of retroperitoneal abscesses. Ann Surg. 1987;205:276–281.
5. Tunuguntla A, Raza R, Hudgins L. Diagnostic and therapeutic difficulties in retroperitoneal abscess. South Med J. 2004;97:1107–1109.
ADDITIONAL READING
• Brook I. Microbiology and management of abdominal infections. Dig Dis Sci. 2008;53:2585–2591.
• 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;19:245–254.
• Negus S, Sidhu PS. MRI of retroperitoneal collections: A comparison with CT. Br J Radiol. 2000;73:907–912.
See Also (Topic, Algorithm, Media)
• Psoas Abscess, Urologic Considerations
• Renal and Perirenal Abscess
• Retroperitoneal Abscess Image 
• Retroperitoneal Hematoma
• Retroperitoneal Mass and Cysts
CODES
ICD9
• 567.31 Psoas muscle abscess
• 567.38 Other retroperitoneal abscess
• 998.59 Other postoperative infection
ICD10
• K68.11 Postprocedural retroperitoneal abscess
• K68.12 Psoas muscle abscess
• K68.19 Other retroperitoneal abscess
CLINICAL/SURGICAL PEARLS
• Nonspecific signs and symptoms frequently lead to a delay in diagnosis and treatment.
• Early percutaneous drainage is essential in lesions >3 cm.