Neurosurgery notes/Infection/Spinal infection/Psoas abscess

Psoas abscess

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Spinal infection

General

  • Applied anatomy of psoas muscle
    • One of 2 heads of the iliopsoas muscle (the other head is iliacus)
    • Origin: inner surface of ilium, base of sacrum, and transverse processes, vertebral bodies (VB) and intervertebral discs of spinal column starting from the inferior margin of T12 VB, extending to the upper part of L5 VB.
    • Insertion: lesser trochanter of the femur.
    • Psoas is the primary hip flexor
    • 30% of people also have a psoas minor which lies anterior to the psoas major
    • Innervation: branches of L2–4 nerve roots proximal to the formation of the femoral nerve
    • Susceptibility to infection
      • Rich vascular supply makes it vulnerable to hematogenous spread
      • Proximity to structures that may be a source of infection
        • Sigmoid colon
        • Jejunum
        • Vermiform appendix
        • Ureters
        • Aorta
        • Renal pelvis
        • Pancreas
        • Iliac lymph nodes
        • Spine

Aetiology

  • Primary (no identifiable underlying disease)
  • Secondary
      • Organ system
      Condition
      Gastrointestinal
      Diverticulitis, appendicitis, Crohn’s disease, colorectal cancer
      Genitourinary
      UTI, cancer
      Musculoskeletal infections
      Vertebral osteomyelitis, infectious sacroiliitis, septic arthritis
      Other
      Endocarditis, femoral artery catheterization, infected abdominal aortic aneurysm graft, hepatocellular Ca, intrauterine contraceptive device, trauma, sepsis, dialysis (peritoneal or long-term hemodialysis)

Risk factors

  • IV drug abuse,
  • HIV/AIDS,
  • Age > 65 years,
  • DM,
  • Immunosuppression
  • Renal failure

Clinical features

  • Signs of iliopsoas inflammation include
    • Active: pain on flexing the hip against resistance
    • Passive: with the patient lying on the unaffected side, hyperextension of the affected hip stretches the psoas muscle and produces pain

Diagnostic tests

  • Routine infection work-up
    • WBC (often elevated),
    • Blood cultures,
    • U/A+C&S (pyuria may be seen)
  • AP abdominal X-ray
    • Psoas shadow may be obliterated
  • CT
    • Sensitivity is 80–100% (MRI is not better).
    • Enlargement of psoas muscle on affected side best seen inside iliac wing

Treatment

  • Often includes drainage of the psoas abscess either surgically or percutaneously with CT guidance. Mortality rates associated with psoas abscess: 2.4% with primary, 19% with secondary, with sepsis being the usual cause ofdeath.