Cerebral abcess

Question 1

what is the etiology of cerebral abcess ?

Answer 1

primary source of infection - which has seen a spread

If frontal sinuses or teeth are the source, the likely organism will be Strep. milleri (microaerophilic)
or
or oropharyngeal anaerobes

In ear abscesses, B. fragilis or other anaerobes are most common

Bacterial abscesses are often peripheral; toxoplasma lesions 
are deeper (eg basal ganglia)

otitis media , mastoiditis

sinusitis seen in men with streptococcus milleri

dental infection

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direct infection from head trauma or neurosurgery

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Common sites of contiguous spread
Temporal lobe and cerebellum (from otogenic infections)
Frontal lobe (from sinus infections)

Question 2

what re the most common pathogens of brain abscess ?

Answer 2

most commonly polymicrobial:

secondary to sinusitis - strep viridian’s
staph aureus
coagulase negative staph

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less common pathogens

bactericides - due to dental infections

gram negative aerobic bacteria - enterobacteria and pseudomonas species

in immunocompromised - toxoplasma , aspergillus

Question 3

pathophysio of brain abscess

Answer 3

Hematogenous spread of pathogens is associated with multiple brain abscesses.
Single abscess is associated with contiguous spread (e.g., otitis media/mastoiditis).

Early cerebritis
Occurs during the first 3–5 days
Infiltration of neutrophils and cerebral edema

Late cerebritis
Occurs after 2–3 weeks
Necrosis, liquefaction, and infiltration of macrophages
Eventually results in the formation of a fibrotic capsule around the lesion

Question 4

clinical features of brain abscess?

Answer 4

Dull persistent headache (a ruptured abscess is associated with a sudden worsening of headache and meningism)

signs of rICP

igns of sepsis else- where (eg teeth, ears, lungs, endocarditis)

Focal neurological deficits -commonly oculomotor nerve palsy or abducens nerve palsy secondary to increased intracranial pressure

Symptoms of increased intracranial pressure (e.g., vomiting, papilledema, altered mental status)

Fever

Generalized or focal seizures

Question 5

what is the diagnosis of cerebral abscess?

Answer 5

Laboratory tests
↑ CRP, ↑ ESR
Leukocytosis

Blood cultures

Lumbar puncture
Contraindicated in the presence of raised intracranial pressure (risk of uncal herniation) !!!!!!!
elevated protein, normal glucose, sterile cultures, and high WBC

/MRI - more sensitive than ct
t1
Best initial diagnostic test
intraparenchymal lesions with a central hypo intense (necrotic) area and peripheral ring enhancement

ct
outer hypodense and inner hyperdense rim (double rim sign) in most cases
central low attenuation (fluid/pus)
surrounding low density (vasogenic oedema)

Biopsy (and drainage): microscopic examination and culture
Best confirmatory test
Entails either craniotomy for complete excision or image-guided aspiration
Distinguishes an abscess from a tumor
Cultures also determine the infective organism and its antibiotic sensitivities.

Question 6

dd?

Answer 6

Other intracranial lesions with ring enhancement:
Neurocysticercosis
Toxoplasmosis
Primary CNS lymphoma
Brain metastases 
Subacute hemorrhage and/or infarction

Question 7

acute management of brain abscess?

Answer 7

Early surgical drainage and biopsy of the abscess

Empiric antibiotic therapy for pyogenic brain abscess: IV antibiotic therapy for 6–8 weeks
Indications
Antibiotic therapy without surgical drainage may be attempted if brain abscess < 2.5 cm,
history of symptoms < 1 week, and no signs of ICP

In all other cases antibiotic therapy should be started immediately after abscess biopsy/drainage

Initial empirical therapy (e.g., third-generation cephalosporin PLUS metronidazole with/without vancomycin)

Specific antibiotics may be used once the causative organisms and their antibiotic sensitivities are known.

Intracranial pressure management: e.g., dexamethasone

Seizure prophylaxis (e.g., anticonvulsants)