CNS infections - Neurosurgery (NS)

Question 1

List pathogens causing brain abscess

Answer 1

Cultures from cerebral abscesses are sterile in up to 25% of cases.

In general: Streptococcus is the most frequent organism.

Multiple organisms may be cultured to varying degrees.

Post traumatic and following neurosurgical procedures is usually due to Staph. Aureus or Enterobacteriacae.

Fungal infections are more common in immune-compromised patients.

Gram negatives are more common in Infants

Question 2

Stages of parenchymal abscess formation

Answer 2

early cerebritis (days 1–3):
Early infection & inflammation, poorly demarcated from surrounding brain, toxic changes in neurons, perivascular infiltrates

late cerebritis (days 4–9): reticular matrix (collagen precursor) & developing necrotic center

early capsule (days 10–13): neovascularity, necrotic center, reticular network surrounds (less well developed along the side facing ventricles)

late capsule (> day 14): collagen capsule, necrotic center, gliosis around capsule

Question 3

List the manifestations of Parenchymal abscess

Answer 3

1. Increased ICP (headache, vomiting, papilledema).
2. Changes in mental state that can progress to coma.
3. Focal neurological deficit according to the site of the lesion with hemiparesis and seizure in 30 – 50% of the cases. While the frontal and temporal lobes are most frequently affected through direct spread of infection, the parietal lobes are mostly affected by through hematogenous spread.
4. Presentation in newborns: cranial enlargement, seizures, irritability, failure to thrive.
5. Meningeal irritation signs (meningism).
6. Systemic features of infection including fever are frequently absent, and if present, fever is usually low grade.

Question 4

Investigations used in Parenchymal abscess

Answer 4

1. Laboratory investigations:
   a) Infection markers usually demonstrate leucocytosis and raised ESR and CRP, but may initially be normal.
   b) Blood culture: may demonstrate the organism but may be normal after starting treatment with antibiotics.
2. Radiological investigations (ring enhancing lesion):
   a) CT with contrast:
   * Confirm the diagnosis by demonstrating the cerebritis or the abscess.
   * Also, opacification of the sinuses or mastoids (sinusitis and mastoiditis) can be recognized.
   * The abscess image is a single or multiple masses with low attenuation surrounded by smooth, symmetric ring-enhancement with variable oedema.
   b) MRI with contrast:
   * Demonstrate similar findings like CT with more details.
   * Features vary according to stage either cerebritis or capsular.

Question 5

Dd in Parenchymal abscess

Answer 5

Mnemonic: MAGIC DR
Metastasis
Abscess
Glioblastoma
Infarction
Contusion
Demyelinating disease
Radiation necrosis

Question 6

Management of parenchymal abcess

Answer 6

• Brain abscess is a medical emergency.
• The principles of treatment are drainage or excision of the abscess, identification of the bacterial organism, long-term intravenous antibiotic therapy (6-8 weeks), correction of the primary source and management of complications (e.g. hydrocephalus).
• Initial antibiotics should be chosen according to the suspected pathogen (i.e. empirical).
• Change the type of antibiotic according to culture and sensitivity (i.e. culture based).