Pathogenesis

The agent causing a spinal abscess is usually bacterial, spreading from a septic focus within bone, or alternatively, from a distant focus through a haematogenous route.

The key organisms are:

• Staphylococcus spp. - the most common
• Streptococcus spp.
• gram -ve bacilli - secondary to diverticulitis and chronic inflammatory bowel disease sources
• Mycobacterium tuberculosis - rare in the UK, but worldwide it is an important cause of chronic epidural abscesses

The dura usually limit the spread of pus to the extradural space, however penetrating wounds and poor immune function may permit subdural and intramedullary spread.