Abscesses and other CNS infections

Question 1

What are the 7 kinds of primary bacterial infections in the CNS?

Answer 1

1) Meningitis
2) Encephalitis
3) Ventriculitis
4) Brain abscess
5) Ventriculoperitoneal shunt and external ventricular drain infection
6) Subdural empyema
7) Eye infections

Question 2

What is a brain abscess?

Answer 2

A focal suppurative (pus forming) process withing the brain parenchyma (pus in the substance of the brain)

Question 3

Are brain abscesses often polymicrobial or monomicrobial?

Answer 3

Polymicrobial (infected with more than one organism)

Question 4

What bacteria are found in 60-70% of brain abscesses?

Answer 4

Streptococci eg. streptococcus milleri (group of pus-forming streptococci)

Question 5

What bacteria is the most common causes of brain abscess following surgery?

Answer 5

Staphylococcus aureus

Question 6

Other than streptococci and staph aureus which 2 other types of bacteria cause brain abscesses?

Answer 6

1) Anaerobes

2) Gram negative enteric bacteria

Question 7

Give 5 less common causes of brain abscesses?

Answer 7

1) Fungi
2) Mycobacterium tuberculosis
3) Toxoplasma gondii
4) Nocardia
5) Actinomyces

Question 8

In what 4 clinical settings do brain abscesses develop?

Answer 8

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%

Question 9

What are the 11 parts of the clinical presentation of brain abscesses?

Answer 9

1) Headache (most common)
2) Focal neurological defect (30-50%)
3) Confusion
4) Fever (

Question 10

What is the mainstay of treatment for a brain abscess?

Answer 10

Drainage

Question 11

For what 5 reasons is it necessary to drain a brain abscess?

Answer 11

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

Question 12

Why is treatment of brain abscesses with Abx difficult?

Answer 12

• 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

Question 13

What 6 Abx can achieve therapeutic concentrations in intracranial pus?

Answer 13

1) Ampicillin
2) Penicillin
3) Cefuroxime
4) Cefotaxime
5) Ceftazidime
6) Metronidazole

Question 14

What would be the empirical treatment regime for a sinugenic/odontogenic abscess?

Answer 14

IV cefotaxime 2g 6-hourly

IV metronidazole 500mg 8-hourly

Question 15

What would be the empirical treatment for and otogenic abscess?

Answer 15

IV benzyl penicillin 2.4g 6-hourly
IV ceftazidime 2g 8-hourly
IV metronidazole 500mg 8-hourly

Question 16

What are the 2 major complications of a brain abscess?

Answer 16

1) Raised intracranial pressure, mass effect, coning

2) Rupture (usually into ventricles) causing ventriculitis

Question 17

What is a subdural empyema?

Answer 17

Infection between dura and arachnoid mata

Question 18

Why do the treatment regimes of otogenic and sinugenic/odontogenic abscesses differ?

Answer 18

Likely causes by different organisms

Question 19

Are subdural empyemas usually monomicrobial or polymicrobial?

Answer 19

Polymicrobial

Question 20

What are the 6 common causes of subdural empyema?

Answer 20

1) Anaerobes
2) Streptococci
3) Aerobic gram negative bacilli
4) Streptococcus pneumonia
5) Haemophilus influenza
6) Staphylococcus aureus

Question 21

What are the 5 common pathogenic mechanisms of subdural empyema?

Answer 21

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

Question 22

What are the 6 possible features of a clinical presentation of subdural empyema?

Answer 22

1) Headache
2) Fever
3) Focal neurological defect
4) Confusion
5) Seizure
6) Coma

Question 23

What is the management of subdural empyema?

Answer 23

• Urgent surgical drainage of pus

- Antimicrobial agents (culture of pus guides abx therapy)

Question 24

What is a ventriculoperitoneal shunt (VP shunt), what is it used to treat?

Answer 24

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

Question 25

What is an external ventricular drain (EVD), what is it used for?

Answer 25

Drain from the ventricles of the brain through a bore hole to the outside world
Temporary tube used to monitor intracranial pressure

Question 26

Colonisation of VPs and EVDs leads to what infection?

Answer 26

Ventriculitis

Question 27

How is ventriculitis diagnosed?

Answer 27

CSF microscopy and culture

Question 28

What is the treatment of VP shunt and EVD infection?

Answer 28

Removal of device and intraventricular Abx