Intracranial abscess
- Intracranial abscesses are rare but require prompt recognition
- Intracranial pus may be
- Extradural
- Subdural
- Intracerebral
- Delayed diagnosis often results in disability or death
- Most are bacterial infections that reach the CNS by:
- Inoculation from penetrating wound
- Spread from adjacent infective focus (e.g. otitis media, sinusitis)
- Blood-borne spread from distant focus (e.g. endocarditic, lung abscess, dental caries)
- In 20% no source of infection is identified
- In United Kingdom otitis media and sinusitis are commonest causes
Pathology
- From local focus of infection bacteria penetrate skull through diploeic veins
- Local osteomyelitis results in venous sinus thrombosis
- Pus in extradural space causes an empyema
- Dura is normally a good barrier to the intracranial spread of infection
- Subdural empyema causes oedema and cortical venous thrombosis
- Brain penetration causes an early diffuse cerebritis
- A localised abscess develops with oedema and increased ICP
- The abscess usually forms in subcortical white matter near to septic focus
- Haematogenous abscesses may be multiple
Clinical presentation
- Can affect any age or sex
- Systemic upset is often mild
- Symptoms of increased ICP include headache, vomiting
- Often associated with progressive clouding of consciousness
- As abscess develops focal neurological symptoms appear
- Symptoms of increased ICP with focal signs requires urgent neurosurgical assessment
- Differential diagnosis includes meningitis or intracranial tumour
Investigations
- CT is investigation of choice
- Cerebral abscess appears as radiolucent space occupying lesion
- Ring enhancement of capsule occurs in contrast enhanced scans
- Often surrounded by considerable oedema
- Position, size and number of abscesses may suggest underlying pathology
- Lumbar puncture is contraindicated
- In presence of raised ICP can precipitate tentorial or tonsillar herniation
Management
- The principles of treatment are:
- Drain intracranial collection
- Administer effective antibiotic therapy
- Eliminate primary source of infection
- Supratentorial abscesses can be drained via a burr hole
- Pus should be aspirated and sent for culture
- Clinical progress can be monitored by serial CT scans
- Stereotactic drainage may be required for multiple or multiloculated abscesses
- Cerebellar abscess may require a suboccipital craniectomy and open drainage
- Subdural empyemas are often diffuse and difficult to drain
- May require craniectomy and open drainage
- Parenteral antibiotic should be administered for at least two weeks
- Choice of antibiotics depends on primary pathology and sensitivities
Outcome
- Prompt treatment results in mortality less than 10%
- Delayed treatment results in mortality greater than 50%
- 50% of survivors have neurological sequelae
- These include hemiparesis, visual field losses and epilepsy
Extradural abscess
- Usually associated with osteomyelitis due to frontal sinusitis or middle ear disease
- Produces localised swelling (Pott's puffy tumour)
- Treatment usually requires removal of infected bone
- Dura is a good barrier to spread of infection
- Intradural extension of infection is rare
Picture provided by David Grayson, Hawke's Bay Hospital, Hastings, New Zealand
Spinal abscess
- Spinal abscesses are usually bacterial
- Infection arises in adjacent bone or by haematogenous spread
- Commonest organisms are staphylococcal and streptococcal species
- Pus is usually confined to extradural space
- Subdural and intramedullary infections are rare
Clinical features
- Patient is often systemically unwell
- Often present with severe thoracic pain at level of abscess
- The pain is worse on movement and associated with marked spasm and tenderness
- Radicular signs are often present at level of lesion
- Cord compression results in long tract signs
- Thrombophlebitis can cause cord vessel thrombosis and cord infarction
- Precipitates complete paralysis, sensory and sphincter loss
Investigations
- Serum white cell count, ESR and CRP are invariably raised
- X-rays are often normal
- May show soft tissue swelling or vertebral collapse
- MRI is investigations of choice
Management
- High index of suspicion is required to make the diagnosis
- Once identified prompt neurosurgical assessment is requires
- If vertebral body collapse consider anterior decompression and stabilisation
- If no vertebral collapse laminectomy or CT guided aspiration may be appropriate
Bibliography
Goldberg A N, Oroszlam G, Anderson T. Complications of frontal sinusitis and their
management. Otolaryngol Clin North Am 2001; 34: 211-225.
Tattersall R, Tattersall R. Pott's puffy tumour. Lancet 2002; 359:
1060-63. |