Spondylodiscitis

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

Spondylodiscitis has a bimodal age distribution, which many authors consider essentially as separate entities:

  • paediatric
  • older population ~50 years

The typical presentation is usually fever and back pain. Patients are often bacteraemic from sources such as endocarditis and intravenous drug use.

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

  • remote infection (present in ~25%)
  • ascending infection, e.g. from urogenital tract instrumentation
  • spinal instrumentation or trauma
  • intravenous drug use
  • immunosuppression
  • long-term systemic administration of steroids
  • advanced age
  • diabetes mellitus
  • organ transplantation
  • malnutrition
  • cancer

Elevated serum CRP and/or ESR.

  • Staphylococcus aureus (most common; 60%)
  • Streptococcus viridans (IVDU, immunocompromised)
  • gram-negative organisms, e.g. Enterobacter spp, E. coli
  • Mycobacterium tuberculosis (Pott disease)
  • less common organisms
    • fungal
      • Cryptococcus neoformans,
      • Candida species
      • Histoplasma capsulatum
      • Coccidioidesimmitis
    • Burkholderia pseudomallei (i.e. melioidosis): diabetic patients from northern Australia and parts of Southeast Asia
    • Brucellae species
  • can occur anywhere in the vertebral column but more commonly involves lumbar spine
  • single level involvement (65%)
  • multiple contiguous levels (20%)
  • multiple non-contiguous levels (10%) 

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 or ill definition of the vertebral endplates can be seen. In untreated cases, bony sclerosis may begin to appear in 10-12 weeks.

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

MRI is the imaging modality of choice due to its very high sensitivity and specificity. It is also useful in differentiating between pyogenic, tuberculous, and fungal infections, and 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 centre indicates abscess formation (hard to distinguish inflammatory phlegmon from abscess without contrast)
  • DWI
    • hyperintense in the acute stage
    • hypointense in the chronic stage

The DWI sequence can help to distinguish between the acute and chronic stages of the disease 7.

A bone scan and white cell (WBC) scan may be used to demonstrate increased uptake at the site of infection, and are more sensitive than plain film and CT, but lack specificity. Not infrequently, a WBC scan demonstrates cold spots, a non-specific finding. The classic appearance on multiphase bone scans is increased blood flow and pool activity and associated increased uptake on the standard delayed static images 15. 67Gallium citrate has been used with some success but is hampered by higher dosimetry and inferior imaging characteristics (high effective dose, long half-life time, poor spatial resolution) 14-15.

18F-FDG PET has been demonstrated to possess high sensitivity in detecting spondylodiscitis. As such, infectious spondylodiscitis can virtually be excluded by a negative scan. Dual imaging with PET/CT may thus become the imaging modality of choice, especially in patients with prior surgery and/or implants, where MRI is contraindicated or hampered by artifact 8-11. Specificity is not as high 10,16, but monitoring of treatment results is possible 9.

Non-FDG PET/CT with 68Ga-citrate (an emerging, generator-based tracer) has shown promising results in pilot studies/small series 12-13.

Possible imaging differential considerations include:

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Article information

rID: 4966
Synonyms or Alternate Spellings:
  • Spinal discitis
  • Discitis involving the spine
  • Pyogenic spinal discitis
  • Discitis-osteomyelitis
  • Native vertebral osteomyelitis (NVO)
  • NVO
  • Discitides
  • Diskitis
  • Spondylodiskitis

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Cases and figures

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    Case 1: advanced L2/3
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    Case 2: with psoas abscess
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    Case 3: with endplate erosion
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    Discitis Osteomye...
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    PET/CT
    Case 8: false positive for metastasis
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    Case 9: tuberculous discitis
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    Case 10: L5-S1 with epidural abscesses
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    Case 12: with bilateral psoas abscesses
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