BASICS
Rare purulent collections in the iliopsoas compartment associated with high morbidity and mortality if not promptly diagnosed and treated
DESCRIPTION
- The iliopsoas compartment is a retroperitoneal anatomic space composed of the psoas major, psoas minor, and iliacus muscles, which mediate hip flexion and are innervated by L2 to L4.
- The muscle group originates from the lateral borders of the 12th thoracic to 5th lumbar vertebrae, passes posterior to the inguinal ligament and anterior to the hip joint, inserting on the lesser trochanter.
- Abscesses are primary (hematogenous or lymphatic spread) or secondary (extension of nearby infection).
- Synonym(s): iliopsoas abscess
EPIDEMIOLOGY
- Secondary psoas abscesses are more common, particularly in developed countries. They are often associated with GI or skeletal infection (1).
- Primary psoas abscesses account for approximately 30% of cases worldwide. >90% occur in developing or tropical countries (1, 2, 3).
- 83% of primary cases occur in patients <30 years (4).
- In neonates and children, psoas abscess is more likely to be primary and associated with Staphylococcus aureus (5).
- Secondary psoas abscesses are more common in the elderly due to age-related diseases such as diverticulitis.
Incidence
- Increased incidence due to HIV, IV drug use, and immunosuppressant therapy
- Increased incidence from 0.5 to 6.5 cases per 10,000 hospital admissions from 1993 to 2004 to 2005 to 2007 (3).
- Improvements in cross-sectional imaging likely contribute to increase in diagnosis.
ETIOLOGY AND PATHOPHYSIOLOGY
- Primary psoas abscess results from hematogenous or lymphatic spread of infection from a distant source.
- Primary abscesses are often monomicrobial, with S. aureus as the predominant organism (2).
- Rich blood supply of the iliopsoas muscles predisposes it to primary infection.
- Mycobacterium. tuberculosis and S. aureus are the most common causative organisms in HIV patients (1).
- Secondary psoas abscess results from contiguous spread from nearby musculoskeletal, GI, GU, and vascular structures.
- S. aureus from musculoskeletal source; Escherichia coli, Bacteroides sp., Enterococcus faecalis, Streptococcus viridans from GI source, and Klebsiella pneumonia from GI and GU sources (2,3).
- S. aureus accounts for 88% of secondary cases (6).
- Secondary psoas abscesses from GI or GU sources may be polymicrobial (2,3).
- M. tuberculosis can cause secondary psoas abscess from vertebral, GI, and GU spread.
- Methicillin-resistant Staphylococcus aureus (MRSA) now accounts for up to 25% of cases (7,8).
- Most psoas abscesses are unilateral and solitary, although multiple abscesses may be found in 25% of cases (3). 3% of affected children may have bilateral disease (9).
RISK FACTORS
- Primary psoas abscess
- IV drug use
- Diabetes
- HIV/AIDS
- Active malignancy
- Renal failure
- Other immunocompromised states
- Secondary psoas abscess: skeletal infections (vertebral and pelvic osteomyelitis, spondylodiscitis), GI infections (inflammatory bowel disease, appendicitis, diverticulitis), GU and gynecologic infections, cardiovascular infections (endocarditis and infected aortic aneurysm), and skin infections (3,7,8)
- Complications of hip arthroplasty, spinal surgery, aortic surgery, and kidney transplantation (3)
- Paraspinal abscess, anastomotic bowel leak, and hematoma increase risk for postoperative infection and abscess formation.
- Psoas abscess has been reported following acupuncture (secondary to spinal infection or bowel perforation), trauma with hematoma formation, uterine dilation and evacuation for fetal demise, and tattooing.
COMMONLY ASSOCIATED CONDITIONS
- Primary psoas abscess: IV drug use, diabetes, HIV/AIDS, malignancy, renal failure
- Secondary psoas abscess: skeletal infections, inflammatory bowel disease, appendicitis, diverticulitis, urinary tract infection
DIAGNOSIS
Diagnosis can be difficult, requiring a careful history, physical examination, and appropriate imaging.
- CT scan is the preferred imaging modality; definitive diagnosis through image-guided drainage and culture
- There is a definitive microbiologic diagnosis occurs in ~75% of cases (2).
HISTORY
- Symptoms are often nonspecific and include fever, flank or abdominal pain, with or without radiation to the anterior hip and thigh. The most common symptoms are fever, back pain, abdominal pain, and limp; guarding, rebound and signs of peritoneal inflammation are less common (1,10).
- Additional symptoms include nausea, anorexia, malaise, weight loss, groin lump, and a limp.
- The classic triad (described by Mynter in 1881) of fever, abdominal/flank pain, and limp is rare (1).
- Most patients present with pain (>50%) and a persistent low-grade fever (25-75%) (2,3,11).
PHYSICAL EXAM
- Maneuvers that stretch or contract the inflamed psoas compartment result in pain on the affected side.
- Pain with extension and internal rotation of the hip (the "psoas sign"ť-sensitivity of 16% and a specificity of 95%) is the most common exam finding (12).
- Psoas sign is elicited by placing a hand proximal to the knee on the affected side and asking the patient to raise the thigh against resistance.
- Alternative: Lay on the unaffected side and hyperextend the contralateral hip to stretch the psoas muscle-positive test if painful.
- Psoas maneuvers may be positive in other conditions causing iliopsoas inflammation, including retrocecal appendicitis.
- Rectal examination helps differentiate psoas abscess from retrocecal appendicitis; pain on palpation of the retrovesical pouch is more consistent with appendicitis.
- Patients with psoas abscess often hold the hip in flexion to relieve pain; patients with hip pathology experience heightened pain with hip flexion.
- Distal extension of a psoas abscess may create a mass palpable below the inguinal ligament.
- Most common findings in neonates include leg or groin swelling, limitation of leg motion, pain, and fever (5).
DIFFERENTIAL DIAGNOSIS
Retrocecal appendicitis, diverticulitis, septic arthritis, avascular necrosis of the hip, renal colic, pyelonephritis, arthritis, disc herniation, inflammatory bowel disease, epidural abscess, vertebral osteomyelitis, endometriosis, pelvic inflammatory disease, hematoma, tumor, and inflammation of the iliopsoas compartment
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
- WBC (elevation >10,000/mL)
- Anemia (hemoglobin <11 g/L)
- Elevated ESR and CRP
- Liver enzymes and creatinine may be elevated (3).
- CT is the recommended imaging modality (13)[B].
- Sensitivity between 88% and 100%
- Typically reveals a focal, hypodense lesion
- May demonstrate:
- Enlargement of the iliopsoas muscle
- Gas or air fluid levels within the muscle and fat stranding
- Contrast CT may show rim enhancement.
- CT helps guide percutaneous drainage.
- MRI cannot be used for percutaneous drainage (1,10).
- Plain abdominal radiographs occasionally outline an inflammatory mass.
- Chest plain films may identify small pleural effusions or raised hemidiaphragm.
- Ultrasound (US) is the recommended initial imaging modality for pediatric or neonatal psoas abscess; CT or MRI provide further classification (5)[B].
- US and MRI are the imaging modalities of choice for pregnant women (10)[C].
Diagnostic Procedures/Other
- Gram stain and culture of blood and aspirated abscess fluid confirms diagnosis and guides antimicrobial treatment.
- AFB stain and mycobacterial culture if TB suspected
TREATMENT
- Most cases require percutaneous (PCD) or open surgical drainage with parenteral antibiotic treatment (16-20% success rate with antibiotics alone) (10)[B].
- CT-guided PCD is the initial procedure of choice. Successful decompression is noted in at least 50% of cases and almost all following a second drainage.
- PCD is associated with a shorter hospital stay.
- Suitable for patients intolerant of general anesthesia (10,14)[B]
- Open drainage indicated for large, complex, or multiloculated abscesses, significant involvement of adjacent structures or if PCD fails
- Primary surgical intervention is more likely to be successful in patients with gas-forming abscess (14)[B].
- Psoas abscesses associated with inflammatory bowel disease, ruptured appendicitis, or infected aortic ruptures are effectively managed with open drainage and surgical treatment of the underlying disease.
- Consider retroperitoneoscopic drainage for complicated tuberculous psoas abscess (15)[B].
- Consider US-guided percutaneous drainage as an alternative to surgical drainage for neonatal and pediatric psoas abscess (5)[B].
MEDICATION
- Broad-spectrum empiric antibiotics targeting staphylococcal (primary and secondary due to skeletal infections) and enteric organisms (secondary to intra-abdominal infection)
- IV monotherapy with ticarcillin clavulanic acid 3.1 g IV q6h, piperacillin-tazobactam 3.375 g IV q6h, or Meropenem 1 g q8h is effective as initial treatment.
- Dual therapy with a 3rd-generation cephalosporin, such as ceftriaxone 1 g IV q12-24h with metronidazole 500 mg IV q8h, is also adequate.
- Treat MRSA infection with vancomycin 15 mg/kg IV q8-12h. Daptomycin 6 mg/kg IV once daily or linezolid 600 mg IV/PO twice daily are alternatives (16)[C].
- Culture results should guide antibiotic coverage.
- Although most psoas abscesses require drainage, those ≤3 cm have been successfully managed by antibiotics alone.
- Treat TB per USPSTF and IDSA guidelines.
ONGOING CARE
Following drainage, pigtail catheter placement permits continued decompression of the abscess cavity and monitoring of purulent output.
FOLLOW-UP RECOMMENDATIONS
Tailor duration of antibiotic treatment to the patient. Most require 3 to 6 weeks. TB requires 9 to 12 months.
Patient Monitoring
Follow-up imaging can verify adequate resolution.
DIET
NPO for percutaneous and surgical drainage procedures
PROGNOSIS
- A high index of suspicion is crucial, as early intervention is associated with favorable outcomes.
- Delays in diagnosis can lead to serious complications, including septic shock (20% of cases).
- Mortality ranges from 5% to 25% with prompt treatment. Untreated cases have ~100% mortality (2,3,7,10,11).
- Mortality increases with age >65 years, multiple comorbidities, bacteremia, sepsis on initial presentation, and high serum creatinine (2,7).
COMPLICATIONS
- Inadequate treatment in patients can lead to unfavorable outcomes. About 40% of patients require >1 drainage procedure for full recovery.
- Incomplete drainage or suboptimal antibiotic treatment may lead to relapses up to a year after initial presentation in 15% of cases (2).
- Spinal cord compression has been reported via direct extension of psoas abscess.
- Most relapses occur within 6 months of follow-up but may occur after 1 year.
REFERENCES
11 Shields D, Robinson P, Crowley TP. Iliopsoas abscess-a review and update on the literature. Int J Surg. 2012;10(9):466-469.22 Navarro L łpez V, Ramos JM, Meseguer V, et al. Microbiology and outcome of iliopsoas abscess in 124 patients. Medicine (Baltimore). 2009;88(2):120-130.33 Tabrizian P, Nguyen SQ, Greenstein A, et al. Management and treatment of iliopsoas abscess. Arch Surg. 2009;144(10):946-949.44 Garner JP, Meiring PD, Ravi K, et al. Psoas abscess-not as rare as we think? Colorectal Dis. 2007;9(3):269-274.55 Okan F, Ince Z, Coban A, et al. Neonatal psoas abscess simulating septic arthritis of the hip: a case report and review of the literature. Turk J Pediatr. 2009;51(4):389-391.66 Ricci MA, Rose FB, Meyer KK. Pyogenic psoas abscess: worldwide variations in etiology. World J Surg. 1986;10(5):834-843.77 Kim YJ, Yoon JH, Kim SI, et al. Etiology and outcome of iliopsoas muscle abscess in Korea; changes over a decade. Int J Surg. 2013;11(10):1056-1059.88 Alonso CD, Barclay S, Tao X, et al. Increasing incidence of iliopsoas abscesses with MRSA as a predominant pathogen. J Infect. 2011;63(1):1-7.99 Bresee JS, Edwards MS. Psoas abscess in children. Pediatr Infect Dis J. 1990;9(3):201-206.1010 Dietrich A, Vaccarezza H, Vaccaro CA. Iliopsoas abscess: presentation, management, and outcomes. Surg Laparosc Endosc Percutan Tech. 2013;23(1):45-48.1111 Wong OF, Ho PL, Lam SK. Retrospective review of clinical presentations, microbiology, and outcomes of patients with psoas abscess. Hong Kong Med J. 2013;19(5):416-423.1212 Navarro Fern ˇndez JA, T ˇrraga L łpez PJ, Rodr ez Montes JA, et al. Validity of tests performed to diagnose acute abdominal pain in patients admitted at an emergency department. Rev Esp Enferm Dig. 2009;101(9):610-618.1313 Yaghmai V, Rosen MP, Lalani T, et al. ACR Appropriateness Criteria ® acute (nonlocalized) abdominal pain and fever or suspected abdominal abscess. Reston: American College of Radiology; 2012:10. https://acsearch.acr.org/docs/69467/Narrative/. Accessed 2014.1414 Hsieh MS, Huang SC, Loh E, et al. Features and treatment modality of iliopsoas abscess and its outcome: a 6-year hospital-based study. BMC Infect Dis. 2013;13:578.1515 B Ľy Ľkbebeci O, Se §kiner I, Karslı B, et al. Retroperitoneoscopic drainage of complicated psoas abscesses in patients with tuberculous lumbar spondylitis. Eur Spine J. 2012;21(3):470-473.1616 Solomkin JS, Mazuski JE, Bradley JS, et al. Diagnosis and management of complicated intra-abdominal infection in adults and children: guidelines by the surgical infection Society and the Infectious Disesases Society of America. Clin Infect Dis. 2010;50(2):133-164.
CODES
ICD10
K68.12 Psoas muscle abscess
ICD9
567.31 Psoas muscle abscess
SNOMED
- Iliopsoas abscess (disorder)
- Abscess iliopsoas non-tuberculous (disorder)
CLINICAL PEARLS
- Psoas abscesses are a rare, retroperitoneal collection of pus resulting from hematogenous, lymphatic, or contiguous spread.
- Primary and secondary psoas abscesses have different underlying causes.
- A high level of suspicion is necessary for diagnosis. Fever and pain are the most common presenting symptoms.
- CT is the imaging modality of choice to diagnose psoas abscess and guide percutaneous drainage.
- Gram stain and culture of aspirated abscess fluid provides definitive diagnosis of causative organisms.
- Prompt drainage and appropriate antibiotic therapy improve outcomes. Percutaneous drainage is the preferred approach.
- Consider underlying morbidities such as inflammatory bowel disease, skeletal infection, HIV, or other immunocompromised states in patients presenting with psoas abscesses.