Incidence: ~ 1.8÷100,000 annually; 0.2–2.8÷10,000 hospital admissions annually

Organism: Staphylococcus aureus including methicillin-resistant S aureus (⅔ of cases); rarely fungus / parasite / mycobacterium

Cause:

1. hematogenous (50%):
   • urinary tract infection (Escherichia coli)
   • pneumonia (Streptococcus pneumoniae)
   • prior soft-tissue / skin infection (S epidermidis)
   • IV drug abuse (Pseudomonas aeruginosa)
2. contiguous infection from adjacent structures (33%):
   • vertebral osteomyelitis, diskitis
   • psoas abscess
3. iatrogenic / penetrating trauma to spine:
   • invasive procedure on spine + nearby structures (Staphylococcus epidermidis)

At risk: acquired immunosuppressive / immunodeficiency disorder, drug addiction, cancer, alcoholism, systemic inflammation / infection, liver disease, diabetes, trauma, surgical procedure involving spine / surrounding structures

Age:>20 years (range, 10 days to 87 years); M÷F = 1.7÷1

• classic triad:
  • localized severe back pain (70%) → radicular pain
  • fever, leukocytosis (60%)
  • neurologic disease (30%): fecal / urinary incontinence with motor / sensory deficit → eventual rapid irreversible neurologic deterioration

Location: thoracic spine (50%)

Site: dorsolateral spanning multiple vertebral levels

Category: (a) focal ≤5 vertebrae (b) diffuse >5 vertebrae

May be associated with:

1. Osteomyelitis
2. Diskitis
3. Paravertebral abscess

N.B.:NO myelography! → may seed infection into subarachnoid space

MR:

• ± effacement of epidural fat + subarachnoid space
• thickening of epidural tissues (early stage):
  • isointense on T1WI
  • moderately hyperintense on T2WI
• liquefied abscess cavity oval-shaped on axial images:
  • hypointense on T1WI + hyperintense on T2WI
    DDx: CSF
• hyperintense at DWI + reduced apparent diffusion coefficient (ADC) ← restricted diffusion

CEMR:

• diffuse heterogeneous / homogeneous enhancement (= phlegmonous infection with microabscesses)
• peripheral enhancement of varying thickness around a central pus collection
• cellulitis surrounding abscess ← inflamed hypervascular tissue (best seen on fat-suppressed CEMR)
• linear enhancement along compressed dura mater (in only 75% of diffuse spinal epidural abscess)
• engorgement of epidural / basivertebral veins (best seen on sagittal images)