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Spondylodiscitis

Spondylodiscitis is characterised by infection involving the intervertebral disc and adjacent vertebrae.

Epidemiology

It has a bimodal age distribution; paediatric and late middle age / older patients (~ 50 years of age) - many authors consider these essentially separate entities.

Clinical presentation

The typical presentation is usually fever and back pain. Often bacteraemic with source such as endocarditis (intravenous drug use)

Pathology

In the paediatric age group infection often starts in the disc itself (direct blood supply still present) whereas in adults infection is thought to begin at the end-plate, and extending into the disc space and then into the adjacent end-plate.  

Risk factors
  • remote infection (present in 20-30%)
  • spinal instrumentation
  • advanced age
  • intravenous drug use
  • immunosupression
  • long-term systemic administration of steroids
  • diabetes mellitus
  • organ transplantation
  • malnutrition
  • cancer
Markers

Elevated serum CRP/ ESR

Infective agents
  • Staphylococcus aureus (most common)
  • Streptococus viridans (IVDU & immunocomprimised)
  • Gram negative organisms
  • Mycobacterium tuberculosis ( Pott's disease
  • Less common agents
    • fungal
      • Cryptococcusneoformans,
      • candida species
      • Histoplasma capsulatum
      • Coccidioidesimmitis
    • Burkholderia pseudomallei (i.e., melioidosis) - diabetic patients from northern Australia and parts of South-east Asia
    • Brucellae spp
Location

Can occur anywhere in the spine but its more common to involving lumbar levels

Radiographic features

Plain film

Plain radiography is insensitive to the early changes of discitis / osteomyelitis, with normal appearances being maintained for up to 2 - 4 weeks. Thereafter disc space narrowing and irregularity / ill definition of the end-plates can be seen. In untreated cases, bony sclerosis may begin to appear in ~ 10 - 12 weeks.

CT

CT findings are similar to plain film, but more sensitive to earlier change. Additionally surrounding soft tissue swelling, collection and even epidural abscesses may be evident.

MRI

This is the imaging modality of choice due to very high sensitivity and specificity. Also useful in differentiation between pyogenic infection, tuberculous / fungal infection or a neoplastic process. 

Signal characteristics include

  • T1
    • low signal in disc space (fluid)
    • low signal in adjacent endplates (bone marrow oedema)
  • T2 - (fat sat or STIR especially useful)
    • high signal in disc space (fluid)
    • high signal in adjacent endplates (bone marrow oedema)
    • loss of low signal cortex at endplates
    • high signal in paravertebral soft tissues
  • T1 C+ (Gd)
    • peripheral enhancement around fluid collection(s)
    • enhancement of vertebral endplates
    • enhancement of perivertebral soft tissues
    • enhancement around low density center indicates abscess formation (hard to distinguish inflammatory phlegmon from abscess without contrast)
  • DWI
    • ​hyperintense in acute stage 
    • hypointense in chronic stage

DWI sequence can help to distinguish acute from chronic stage of the disease7.

Nuclear medicine

A bone scan and white cell scan may be used to demonstrate increased uptake at the site of infection, and are more sensitive than plain film and CT, however lack specificity. The classic appearance on multiphase bone scans is increased blood flow and pool activity and associated increased uptake on the standard delayed static images.

Differential diagnosis

Possible imaging differential considerations include

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