Abscesses and other CNS infections Flashcards
What are the 7 kinds of primary bacterial infections in the CNS?
1) Meningitis
2) Encephalitis
3) Ventriculitis
4) Brain abscess
5) Ventriculoperitoneal shunt and external ventricular drain infection
6) Subdural empyema
7) Eye infections
What is a brain abscess?
A focal suppurative (pus forming) process withing the brain parenchyma (pus in the substance of the brain)
Are brain abscesses often polymicrobial or monomicrobial?
Polymicrobial (infected with more than one organism)
What bacteria are found in 60-70% of brain abscesses?
Streptococci eg. streptococcus milleri (group of pus-forming streptococci)
What bacteria is the most common causes of brain abscess following surgery?
Staphylococcus aureus
Other than streptococci and staph aureus which 2 other types of bacteria cause brain abscesses?
1) Anaerobes
2) Gram negative enteric bacteria
Give 5 less common causes of brain abscesses?
1) Fungi
2) Mycobacterium tuberculosis
3) Toxoplasma gondii
4) Nocardia
5) Actinomyces
In what 4 clinical settings do brain abscesses develop?
1) Direct spread for contiguous (sharing common border) suupurative focus - eg. ear, sinuses, teeth
2) Haematogenous spread from a distant focus - eg. endocarditis, bronchiectasis (often multiple abscesses)
3) Trauma - eg. open cranial fracture, post neurosurgery
4) Cryptogenic (unknown origin) - 15-20%
What are the 11 parts of the clinical presentation of brain abscesses?
1) Headache (most common)
2) Focal neurological defect (30-50%)
3) Confusion
4) Fever (
What is the mainstay of treatment for a brain abscess?
Drainage
For what 5 reasons is it necessary to drain a brain abscess?
1) To urgently reduce intracranial pressure
2) To confirm diagnosis
3) To obtain pus for microbiological investigation
4) To enhance efficacy of Abx
5) To avoid spread of infection into the ventricles
Why is treatment of brain abscesses with Abx difficult?
- The physiological properties of the blood-brain barrier and the blood-CSF barrier are distinct
- Penetration of drugs into the CSF and brain tissue differ
- Can make it hard to achieve therapeutic concentrations in intracranial pus
What 6 Abx can achieve therapeutic concentrations in intracranial pus?
1) Ampicillin
2) Penicillin
3) Cefuroxime
4) Cefotaxime
5) Ceftazidime
6) Metronidazole
What would be the empirical treatment regime for a sinugenic/odontogenic abscess?
IV cefotaxime 2g 6-hourly
IV metronidazole 500mg 8-hourly
What would be the empirical treatment for and otogenic abscess?
IV benzyl penicillin 2.4g 6-hourly
IV ceftazidime 2g 8-hourly
IV metronidazole 500mg 8-hourly
What are the 2 major complications of a brain abscess?
1) Raised intracranial pressure, mass effect, coning
2) Rupture (usually into ventricles) causing ventriculitis
What is a subdural empyema?
Infection between dura and arachnoid mata
Why do the treatment regimes of otogenic and sinugenic/odontogenic abscesses differ?
Likely causes by different organisms
Are subdural empyemas usually monomicrobial or polymicrobial?
Polymicrobial
What are the 6 common causes of subdural empyema?
1) Anaerobes
2) Streptococci
3) Aerobic gram negative bacilli
4) Streptococcus pneumonia
5) Haemophilus influenza
6) Staphylococcus aureus
What are the 5 common pathogenic mechanisms of subdural empyema?
1) Spread of infection from sinuses (50-80%)
2) Spread of infection from middle ear
3) Spread of infection from mastoid
4) Spread of infection from distant site (haematogenous spread)
5) Following surgery or trauma
What are the 6 possible features of a clinical presentation of subdural empyema?
1) Headache
2) Fever
3) Focal neurological defect
4) Confusion
5) Seizure
6) Coma
What is the management of subdural empyema?
- Urgent surgical drainage of pus
- Antimicrobial agents (culture of pus guides abx therapy)
What is a ventriculoperitoneal shunt (VP shunt), what is it used to treat?
Tube from ventricles, through brain parenchym and subcutaneously across the thorax to drain into peritoneal cavity through a series of fenestrations
Free movement of CSF out of ventricles into peritoneum where it is re-absorbed
Permanent tube used to treat for hydrocephalus
What is an external ventricular drain (EVD), what is it used for?
Drain from the ventricles of the brain through a bore hole to the outside world
Temporary tube used to monitor intracranial pressure
Colonisation of VPs and EVDs leads to what infection?
Ventriculitis
How is ventriculitis diagnosed?
CSF microscopy and culture
What is the treatment of VP shunt and EVD infection?
Removal of device and intraventricular Abx
