spinal epidural abscess

Spinal
epidural abscess • Post-operative pyogenic spondylodiscitis and epidural abscess - Ganzer Fall bei Radiopaedia
ElBeialy M, Post-operative pyogenic spondylodiscitis and epidural abscess. Case study, Radiopaedia.org (Accessed on 23 Jan 2023) https://doi.org/10.53347/rID-25795 • CC by-nc-sa 3.0 (modified)
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Spinal epidural abscess represents infection of the epidural space, located between the spinal dura mater and the vertebral periosteum. It can present with rapidly deteriorating neurological function due to compression. Imaging is best performed with MRI and emergency surgery is often required.

Epidemiology

Spinal epidural abscess is an uncommon condition with an estimated incidence of 2-3 per 10,000 hospital admissions. It has a peak incidence in the fifth-to-seventh decades of life with a male predominance, which might be due to predisposing conditions and risk factors that are more prevalent in older people . Risk factors include :

  • comorbidities: diabetes mellitus, alcohol abuse, HIV infection
  • spinal abnormality or intervention: degenerative joint disease, trauma, surgery or procedure
  • potential local or systemic source of infection: IVDU

Clinical presentation

Many clinical features are non-specific, even in an acute case of a spinal epidural abscess, mainly if there are no demographic or epidemiological clues. Classical symptoms include:

  • spinal pain
  • fever
  • neurological deficit

This triad, however, is only present in 10-15% of the cases at first physician contact. Back pain and severe, circumscribed tenderness are by far the most frequent early findings .

Pathology

Bacteria gain access to the epidural space by three mechanisms:

  • haematogenous dissemination from a remote focal infection
  • direct invasion from a neighboring infected structure: diskitis-osteomyelitis, septic arthritis
  • iatrogenic inoculation: epidural/spinal anesthetics, steroid injections, surgery

The source of infection is not always apparent, and cannot be identified in approximately one-third of the cases . Paralysis may result via spinal compression from a mass-effect exerted by the abscess or secondary ischemia from septic thrombosis .

Radiographic features

Spinal epidural abscess developing from direct spread from neighboring structures are, not surprisingly, usually adjacent to the primary focus.

For example, diskitis-osteomyelitis which is thought to be the primary source of infection in up to 80% of patients , usually results in anterior abscesses . In contrast, when facet joint septic arthritis is the primary infection, collections tend to be posterior or posterolateral. This is the same distribution as what are believed to be cases resulting from a direct haematogenous spread, which is primarily located in the posterior/dorsal aspect of the spinal canal .

Plain radiograph

Plain films have little role to play in investigating a patient with suspected spinal epidural abscess, as no direct visualization of the collection is possible. They can, however, be useful in visualizing established diskitis-osteomyelitis, particularly when MRI (and to a lesser extent CT) are not available.

CT

Despite excellent bony anatomical details, CT even with contrast can struggle to demonstrate smaller collections. It may, however, reveal changes of diskitis-osteomyelitis and facet joint septic arthritis, both by direct visualization of eroded bone/joint, as well as identifying adjacent soft tissue stranding .

MRI

Gadolinium-enhanced MRI is the imaging choice for diagnosis of spinal epidural infection. Diffusion-weighted sequences are useful to confirm infection .

There are two main patterns, with distinct imaging appearances :

  • phlegmonous stage of infection results in homogeneous enhancement of the abnormal area which correlate to granulomatous-thickened tissue with embedded micro-abscess without a significant pus collection
  • liquid abscess surrounded by inflammatory tissue which shows varying degree of peripheral enhancement with gadolinium

    • The key to identifying liquid abscess, which is usually sufficient cause for surgical drainage, is the presence of a region of high T2 signal, with low T1 signal and without enhancement (usually surrounded by a rim of enhancement). DWI/ADC commonly demonstrates restricted diffusion of the abscess content.

    Differential diagnosis

    Conditions to be considered include :

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    epidurale
    intraspinale Raumforderung
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    epiduraler
    Abszess
    www.eurorad.org • CC by-nc-sa-4.0
    intraspinale
    epidurale zystische Raumforderungen
    Wikipedia • CC BY-SA 3.0