4. CNS infections Flashcards
Routes of infection
- Direct implantation
- Trauma
- Meningomyelocele - Local extension
- Sinusitis
- Otitis media
- Dental caries - Hematogenous spread
- Septicaemia
- Infective emboli (e.g. from infective endocarditis)
- Facial infections (retrograde venous spread through anastomoses with veins of face) - Transport along peripheral nervous system
- Rabies virus
- Herpes simplex virus
Pattern of involvement of microbes
Coverings:
- Extra-/subdural abscess: Bacteria
- Meningits: Bacteria, Fungi, Viruses
Brain parenchyma:
- Cerebral abscess: Bacterial, Fungi
- Encephalitis: Viruses, Prions
Both:
Meningo-encephalitis: Viruses
Types of clinical presentations from CNS infections
- Subdural empyema & Extradural abscess
- Meningitis
- Cerebral abscess
- Encephalitis
- Specific pathogen-related CNS infections
Subdural empyema
Direct implantation or local extension (usually bacteria)
Clinical features of subdural empyema
- Spinal tap: similar to that of cerebral abscess
2. Local symptoms, meningitis symptoms
Complications of subdural empyema
Thrombophlebitis of bridging veins leading to cerebral infarction
Treatment of subdural empyema
surgical drainage
Extradural abscess
Direct implantation or local extension (usually bacteria)
Complications of extradural abscess
In the case of a spinal cord epidural infection, it may cause spinal compression, constituting a neurosurgical emergency
Definition of meningitis
Inflammation of the meninges & CSF within the subarachnoid space
Causes of meningitis
- Acute bacterial meningitis
- Aseptic meningitis
- Tuberculous meningitis
Causes of acute bacterial meningitis
- Neonate:
- Escherichia coli
- Listeria monocytogenes
- Group B Streptococci
→ empiric treatment: ampicillin + gentamicin - Child < 5 years old
- Streptococcus pneumoniae
- Haemophilus influenzae
- Neisseria meningitidis
→ empiric treatment: ceftriaxone - Adolescent
- Neisseria meningitidis
→ empiric treatment: ceftriaxone - Adult
- Neisseria meningitidis
- Streptococcus pneumoniae
→ empiric treatment: ceftriaxone - Elderly & Immunocompromised
- Streptococcus pneumoniae
- Haemophilus influenzae
- Neisseria menigitidis
- Listeria monocytogenes
→ empiric treatment: ceftriaxone + ampicillin
Aseptic Meningitis
- Usually viral (enteroviruses such as echovirus & coxsackievirus)
- Commonly causes concomitant encephalitis (viral
meningoencephalitis) - Often self-limiting
Tuberculous Meningitis
- Mycobacterium tuberculosis
- Causes a chronic meningitis often affecting the base
of the brain
Morphology of tuberculous meningitis
Gross appearance:
i) Gelatinous exudate in subarachnoid space often at base of brain
ii) White granules (tubercles) scattered all over meninges
Complications of tuberculous meningitis
- obliterative endarteritis of arteries in subarachnoid space (leading to cerebral ischemia & infarct)
- fibrous adhesive arachnoiditis (leading to cranial nerve palsies & hydrocephalus)
- tuberculoma (producing space-occupying symptoms)
- May cause concomitant encephalitis (tuberculous meningoencephalitis)
Clinical presentation of meningitis
- Headache, fever, malaise
- Photophobia
- Neck stiffness
- Kernig’s sign (leg bent at the knee & hip at 90
degrees, with subsequent extension being painful)