Brain abscesses and other infections of the central nervous system

Question 1

What are the different types of primary bacterial infections of the CNS?

Answer 1

• Meningitis
• Encephalitis
• Ventriculitis
• Brain Abscess
• Ventriculoperitoneal shunt and external ventricular drain infection
• subdural empyema
• (eye infections)

Question 2

What is a brain abscess?

Answer 2

A brain abscess is a focal suppurative process within the brain parenchyma (pus in the substance of the brain)

Question 3

What is the aetiology of brain abscesses?

Answer 3

• Often mixed (polymicrobial) - usually need broad spectrum Abx
• Streptococci (60-70%) e.g. Streptococcus “milleri”
• S. aureus (10-15%) most common after trauma/surgery
• Anaerobes - usually piggyback on other bacteria
• Gram negative enteric bacteria (E.coli, Pseudomonas spp.)
• Others e.g. fungi, Mycobacterium tuberculosis, - Toxoplasma gondii, Nocardia, Actinomyces

Question 4

What is the pathogenesis of brain abcesses?

Answer 4

• Direct spread from “contiguous” suppurative focus (e.g. from middle ear[40%], sinuses, teeth)
• Haematogenous spread from a distant focus e.g. endocarditis, bronchiectasis (often multiple abscesses)
• Trauma (e.g., open cranial fracture, post-neurosurgery)
• Cryptogenic (no focus ~15-20%).

Question 5

What is the clinical presentation of brain abcesses?

Answer 5

• Headache (most common)
• Focal neurological deficit (30-50%)
• Confusion
• Fever (

Question 6

Why is drainage the treatment of choice for brain abscesses?

Answer 6

1. to urgently reduce intracranial pressure
2. to confirm diagnosis
3. to obtain pus for microbiological investigation
4. to enhance efficacy of antibiotics
5. to avoid spread of infection into the ventricles

Question 7

What Abx treatment is given for brain abscesses and why?

Answer 7

• Physiological properties of blood-brain barrier and blood CSF-barrier are distinct
• Penetration of drugs into CSF and brain tissue differ
• Ampicillin, penicillin, cefuroxime, cefotaxime, ceftazidime, and metronidazole achieve therapeutic concentrations in intracranial pus

Question 8

What is the treatment regimen for a sinugenic/odontogenic abscess?

Answer 8

iv cefotaxime 2g 6-hourly +

iv metronidazole 500mg 8-hourly

Question 9

What is the treatment regimen for an otogenic abscess?

Answer 9

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

Question 10

What are the complications of brain abscesses?

Answer 10

• Raised intracranial pressure, mass effect, coning

- Rupture (usually into ventricles) causing ventriculitis

Question 11

What is subdural empyema?

Answer 11

Infection between dura and arachnoid mater.

Question 12

What is the aetiology of subdural empyema?

Answer 12

(often polymicrobial) anaerobes, streptococci, aerobic Gram negative bacilli, Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus

Question 13

What is the pathogenesis of subdural empyema?

Answer 13

Pathogenesis: 
- spread of infection from sinuses (50-80%) 
- middle ear and mastoid (10-20%)
distant site (5%, haematogenous) 
- following surgery or trauma

Question 14

Which of the 3rd generation cephalosporins is one of the few antibiotics active against P. aeruginosa? (common cause of ear infections)

Answer 14

Ceftazidime

Question 15

What is the clinical presentation of subdural empyema?

Answer 15

Headache fever, focal neurological deficit, confusion, seizure, coma

Question 16

What is the treatment for subdural empyema?

Answer 16

Urgent surgical drainage of pus, antimicrobial agents

Question 17

What is the aetiology of ventriculitis?

Answer 17

EVDs and VP shunts can become colonised with organisms that subsequently cause ventriculitis

Question 18

What is the most common cause of ventriculitis due to EVD/VP colonisation?

Answer 18

Coagulase-negative staphylococci

Question 19

What is the treatment for ventriculitis?

Answer 19

Device removal, intraventricular antibiotics