Psoas Abscess

History and Epidemiology

  • First Reports: first described by Mynter in 1881 as “Psoitis”
  • Age Predominance
    • Age 44-58 y/o: peak age group in developed countries
    • Children/Younger Adults: peak age group in developing countries
  • Geographic Distribution: psoas abscess is more common in tropical and developing countries
    • Asia and Africa: 99% of cases are due to primary hematogenous/lymphatic mechanism of spread to the psoas muscle
    • Europe and North America: 17-61% of cases are due to primary hematogenous/lymphatic mechanism of spread to the psoas muscle
  • Sex Predominance: more common in males than females
  • Anatomic Distribution: equal prevalence on right and left

Anatomy

  • Muscles Involved in Hip Flexion: the iliacus and psoas muscles are the main hip flexors (together, they are referred to as the iliopsoas)
    • They are located in the retroperitoneal iliopsoas compartment
  • Psoas Muscle: originates from the transverse processes and the lateral aspects of the T12-L5 vertebrae
    • The psoas continues downward across the pelvic brim, posterior to the inguinal ligament and anterior to the hip joint capsule -> the psoas ultimately forms a tendon that inserts into the lesser trochanter of the femur
    • The iliacus muscle joins the psoas to form this tendon
    • The iliopsoas bursa separates the iliopsoas from the hip capsule: however, in 15% of patients, this bursa communicates with the hip capsule, allowing the spread of infection between the hip joint and the iliopsoas
  • Nearby Anatomic Structures: the psoas is located adjacent to the vertebrae, abdominal aorta, sigmoid colon, appendix, hip joint, and the iliac lymph nodes
    • Infection may spread beween the psoas and these structures

Pathogenesis

  • Definition: psoas abscess is a collection of pus in the iliopsoas muscle compartment
  • Mechanisms of Psoas Muscle Infection: in some cases, the exact mechanism of psoas infection may be impossible to determine
    • Contiguous Spread to Psoas Muscle
    • Hematogenous/Lymphatic Spread to Psoas Muscle: may be an obvious or occult source

Etiology

Hematogenous/Lymphatic Spread to Psoas Muscle (Primary)

  • Risk Factors

Contiguous Spread to Psoas Muscle (Secondary)

  • Abdominal Aortic Aneurysm (Infected)/Aortic Stent Graft (Infected) (see Abdominal Aortic Aneurysm, [[Abdominal Aortic Aneurysm]])
    • May be associated with aorto-duodenal fistula or aortic rupture
  • Gastrointestinal (GI) Tract Disease
    • Acute Pancreatitis (see Acute Pancreatitis, [[Acute Pancreatitis]])
    • Appendicitis (see Appendicitis, [[Appendicitis]])
    • Colon Cancer (see Colon Cancer, [[Colon Cancer]])
    • Diverticulitis (see Diverticulitis, [[Diverticulitis]])
    • Gastrointestinal (GI) Tract Infection
    • Inflammatory Bowel Disease (see Inflammatory Bowel Disease, [[Inflammatory Bowel Disease]])
      • Crohn’s Disease (see Crohn’s Disease, [[Crohns Disease]]): may especially occur in patients with severe ileocolitis
        • Incidence of Psoas Abscess in Crohn’s Disease: 0.4-4.3% [MEDLINE]
      • Ulcerative Colitis (UC) (see Ulcerative Colitis, [[Ulcerative Colitis]])
    • Pancreatic Abscess
  • Genitourinary (GU) Tract Disease
    • Extracorporeal Shock Wave Lithotripsy
    • Renal Abscess/Urinary Tract Infection (UTI) (see Renal Abscess, [[Renal Abscess]])
    • Renal Surgery/Nephrectomy
    • Xanthogranulomatous Pyelonephritis
  • Hip Joint/Arthroplasty Infection
    • One series reported that 12% of their hip arthroplasty infection cases had an accompanying psoas abscess [MEDLINE]: in these cases, hematogenous infection and history of neoplasm were risk factors for the development of psoas abscess
  • Vertebral Osteomyelitis/Vertebral Discitis/Paraspinal Infection
    • Verterbral osteomyelitis is the most common contiguous source of psoas abscess (in such cases, psoas abscess may accompany an epidural abscess)
    • Vertebral osteomyelitis with associated psoas abscess has been reported to occur with epidural catheter use
    • Risk Factors
  • Other
    • Abdominal Surgery
    • Instrumentation of Hip
    • Instrumentation of Inguinal Region
    • Instrumentation of Lumbar Region
    • Trauma

Microbiologic Etiology

Primary-Hematogenous/Lymphatic Spread to Psoas Muscle (usually monomicrobial)

Secondary-Contiguous Spread to Psoas Muscle (monomicrobial or polymicrobial)

  • Anaerobes
  • Candida Albicans (see Candida, [[Candida]])
  • Enteric Organisms
  • Klebsiella Pneumoniae (see Klebsiella Pneumoniae, [[Klebsiella Pneumoniae]]): common in Taiwan (especially in diabetics and in association with urinary tract infection)
  • Nocardiosis (Disseminated) (se Nocardiosis, [[Nocardiosis]])
  • Salmonella (see Salmonella, [[Salmonella]])
  • Streptobacillus Moniliformis (see Streptobacillus Moniliformis, [[Streptobacillus Moniliformis]])
  • Streptococcus Pneumoniae (see Streptococcus Pneumoniae, [[Streptococcus Pneumoniae]])

Diagnosis

Blood Specimen

  • CBC
    • Anemia
    • Leukocytosis
  • C-Reactive Protein (CRP): may be elevated
  • Aspartate Aminotransferase (AST): may be elevated
  • Erythrocyte Sedimentation Rate (ESR): may be elevated
  • Blood Cultures: positive in 41-68% of cases
    • Staphylococcus Aureus is the most commonly isolated organism

Abscess Specimen

  • Culture of Aspirated Abscess Material: may be required to identify the causative organism (in cases with negative blood cultures)
  • Cytology of Aspirated Specimen: useful to exclude tumor as an etiology (in cases where tumor may also be a diagnostic consideration)

Imaging

  • Abdominal/Pelvic CT Scan: most common diagnostic modality (and is diagnostic in almost all cases)
    • Features
      • Focal Hypodense Psoas Lesion
      • Infiltration of Fat SUrrounding Psoas
      • Gas or Air-Fluid Level Within the Psoas
    • Size >6 cm in 39% of cases [MEDLINE]
    • Bilateral in 13% of cases [MEDLINE]
    • Multiple in 25% of cases [MEDLINE]
  • Abdominal/Pelvic MRI: may be used in some cases
    • Improved visualization of soft tissues and vertebrae
  • Abdominal/Pelvic Ultrasound: may be used in some cases, although has a low sensitivity and specificity
  • Chest X-Ray: may demonstrate pleural effusion or elevated hemidiaphragm in some cases
  • Tagged WBC Scan: may demonstrate psoas abscess

Clinical

Time Course of Clinical Symptoms

  • Time Course of Presentation: typically subacute (over weeks) or chronic (over months)
  • Latency to Diagnosis [MEDLINE]
    • Median Latency to Diagnosis: 22 days
    • 33% of Cases: latency >42 days

Classical Triad of Symptoms/Signs

  • Epidemiology
    • Reported by Mynter in 1881 cases
    • Rarely seen today
  • Clinical Features
    • Pain
    • Fever
    • Limp

Typical Symptoms/Signs

  • Anorexia (see Anorexia, [[Anorexia]])
  • Back/Flank/Lower Abdominal Pain (see Back Pain, [[Back Pain]], Flank Pain, [[Flank Pain]], and Abdominal Pain, [[Abdominal Pain]]): 95% of cases
    • Psoas Sign: pain with extension of the hip (as this maneuver stretches the psoas mucscle)
    • Radiation: to hip and/or the posterior thigh
    • Limitation of Hip Movement: common (in contrast to septic hip arthritis, hip pain is decreased with hip flexion)
    • Patient Body Position: patients typically prefer to remain with hips in flexion and with lumbar lordosis
  • Fever (see Fever, [[Fever]]): 26% of cases
  • Gastrointestinal Complaints: 43% of cases
  • Inguinal Mass: in some cases, psoas abscess may extend to present as a painful/painless mass below the inguinal ligament
    • Painless mass is more common with a tuberculosis-related psoas abscess
  • Limp
  • Lower Extremity Edema: 28% of cases
  • Lower Extremity/Hip Pain (see Hip Pain, [[Hip Pain]]): 30% of cases
  • Palpable Abdominal Mass (see Abdominal Mass, [[Abdominal Mass]]): 13% of cases
  • Weight Loss (see Weight Loss, [[Weight Loss]]): 11% of cases

Complications

  • Deep Venous Thrombosis (DVT) (see Deep Venous Thrombosis, [[Deep Venous Thrombosis]]): due to extrinsic compression of the iliac vein
  • Hydronephrosis (see Hydronephrosis, [[Hydronephrosis]]): due to compression of the ureter
  • Paralytic Ileus (see Ileus, [[Ileus]])
  • Septic Shock (see Sepsis, [[Sepsis]]): may occur in up to 20% of cases

Treatment

  • Antibiotics: usually required for approximately 3-6 weeks after drainage has been achieved (or 6 months in cases of tuberculous abscess)
    • Antibiotic therapy alone has been reported to have 78% success rate in some series [MEDLINE]: however, antibiotics alone is typically not the approach of choice
  • Percutaneous Catheter Drainage (usually CT-guided): effective in the majority of cases
  • Laparoscopic or Open Surgical Drainage: may be required in cases that fail percutaneous catheter drainage, cases with difficult to drain multiloculated collections, cases with abscess secondary to bowel disease (in Crohn’s disease), or in cases with significant involvement of adjacent structures (requiring additional resection, etc)

Prognosis

  • Mortality Rate: 5% [MEDLINE]
  • Risk Factors for Mortality
    • Advanced Age
    • Bacteremia
    • Delayed or Inadequate Treatment
    • Infection with E Coli
  • Relapse: can occur up to a year after presentation
    • Relapse has been reported in 15-36% of cases
    • Risk Factors for Relapse
      • Inadequate Drainage
      • Inadequate Antimicrobial Therapy
  • Resolution of Hip Flexion Deformity: may not completely resolve in some cases, due to fibrosis within iliopsoas sheath

References

  • Pyogenic psoas abscess: worldwide variations in etiology. World J Surg. 1986;10(5):834 [MEDLINE]
  • Psoas abscess complicating Crohn’s disease: report of a case. Surg Today. 2000;30(8):759 [MEDLINE]
  • Microbiology and outcome of iliopsoas abscess in 124 patients. Medicine (Baltimore). 2009;88(2):120 [MEDLINE]
  • Management and Treatment of Iliopsoas Abscess. Arch Surg. 2009 Oct;144(10):946-9 [MEDLINE]: retrospective review of 61 cases from 2000 to 2007
  • Association between psoas abscess and prosthetic hip infection: a case-control study. Acta Orthop. 2009;80(2):198 [MEDLINE]
  • Iliopsoas abscess–a review and update on the literature. Int J Surg. 2012;10(9):466-9 [MEDLINE]
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