(27) Abscesses and other CNS infection Flashcards
What are the different types of primary bacterial infections of the central nervous system?
- meningitis
- encephalitis
- ventriculitis
- brain abscess
- ventriculoperitoneal shunt and external ventricular drain infection
- subdural empyema
- eye infections
What is a brain abscess?
A focal suppurative process within the brain parenchyma (pus in the substance of the brain)
Which bacteria cause brain abscesses?
Often mixed (polymicrobial)
- streptococci (60-70%) eg. streptococcus milleri
- staphylococcus aureus (10-15%)
- anaerobes
- gram negative enteric bacteria
- others like fungi, mycobacterium tuberculosis, toxoplasma gondii, nocardia, actinomyces
When is the cause of brain abscess most commonly staphylococcus aureus?
After trauma/surgery
Give examples of gram negative enteric bacteria that may cause brain abscess
- E. coli
- pseudomonas spp.
What are the 4 clinical settings that brain abscesses may develop in? (pathogenesis)
- direct spread from “contagious” suppurative focus
- haematogenous spread from a distant focus
- trauma
- cryptogenic
Brain abscesses might be caused by direct spread from contagious suppurative focus. Give examples
From ear (40%)
From sinuses, from teeth
Brain abscesses might be caused by haematogenous spread from a distant focus. Give examples
- endocarditis
- bronchiectasis (often multiple abscessed)
Brain abscesses might be caused by trauma. Give examples
- open cranial fracture
- post-neurosurgery
How many brain abscesses are cryptogenic (no focus, unknown cause)?
15-20%
What is the typical clinical presentation of brain abscess?
- headache
- focal neurological deficit
- confusion
- fever
- nausea and vomiting
- dizziness, seizures
- neck stiffness
- papilloedema
- coma
What is the most common symptom of bran abscess?
Headache
How often is focal neurological deficit a symptom of brain abscess?
30-50% of patients
How often is fever a symptom of brain abscess?
Papillodema is a potential symptom of brain abscess. What is it?
Optic disc swelling that is caused by increased intracranial pressure. The swelling is usually bilateral and can occur over a period of hours to weeks.
What is the treatment of choice for brain abscess?
Drainage
small abscesses can be treated with antibiotics alone
What are the purposes of drainage in brain abscesses?
- urgently reduce intracranial pressure
- confirm diagnosis
- obtain pus for microbiological investigation
- enhance efficacy of antibiotics
- avoid spread of infection into the ventricles
Penetration of drugs into CSF and brain tissue differ. Which antibiotics achieve therapeutic concentrations in intracranial pus?
- ampicillin
- penicillin
- cefuroxime
- cefotaxime
- ceftazidime
- metronidazole
Give an example of an empirical treatment regimen for sinugenic/odontogenic abscess
cefotaxime 2g 6-hourly +
metronidazole 500mg 8-hourly
Drained abscess: treat for 4-6 weeks
Give and example of an empirical treatment regimen for otogenic abscess
benzyl penicllin 2.4g 6-hourly +
ceftazidime 2g 8-hourly
metronidazole 500mg 8-hourly
Drained abscess: treat for 4-6 weeks
What are the complications associated with brain abscess?
- raised intracranial pressure
- mass effect
- coning
- rupture (usually into ventricles, causing ventriculitis)
What is a subdural empyema?
Infection between dura and arachnoid mater
What are the causes of subdural empyema?
Often polymicrobial
- anaerobes
- streptococci
- aerobic gram negative bacilli
- streptococcus pneumoniae
- haemophilus influenzae
- staphylococcus aureus
Describe the possible pathogenesis in subdural empyema
- spread of infection from sinuses (50-80%)
- spread of infection from middle ear and mastoid (10-20%)
- spread of infection from distant site (haematogenous) (5%)
- following surgery or trauma
