Definition - pus in brain substance, surrounded by tissue reaction (capsule formation)
Etiology
modes of spread: 10-60% of patients have no cause identified
pathogens
Streptococcus (most common), often anaerobic or microaerophilic
Staphylococcus (penetrating injury)
Gram-negatives, anaerobes (Bacteroides, Fusobacterium)
in neonates: Proteus and Citrobacter (exclusively)
immunocompromised: fungi and protozoa (Toxoplasma, Nocardia, Candida albicans, Listeria monocytogenes, Mycobacterium and Aspergillus)
Risk Factors
lung abnormalities [infection, AV fistulas; especially Osler-Weber-Rendu syndrome (aka hereditary hemorrhagic telangiectasia)]
congenital coronary heart disease: R→L shunt bypasses pulmonary filtration of microorganisms
immunosuppression (e.g. AIDS)
dental abscess
Clinical Features
focal neurological signs and symptoms
H/A, decreased LOC; hemiparesis and seizures in 50%
mass effect, increased ICP and sequelae (cranial enlargement in children)
hemiparesis and seizures in 50%
± signs and symptoms of systemic infection (low-grade fever, leukocytosis)
Complications
with abscess rupture: ventriculitis, meningitis, venous sinus thrombosis
transtentorial herniation
Investigations
CT scan often first test in emergency department
MRI
imaging of choice
apparent diffusion coefficient (ADC) used to differentiate abscess (black) from tumour (white)
WBC/ESR may be normal, blood cultures rarely helpful and LP contraindicated if large mass
CSF: non-specific (high ICP, high WBC, high protein, normal carbohydrate), rarely helpful,
usually negative culture
Treatment
aspiration ± excision and send for Gram stain, acid fast bacillus (AFB), C&S, fungal culture
excision preferable if location suitable
antibiotics - empirically: vancomycin + ceftriaxone + metronidazole or chloramphenicol or rifampin (6-8 wk therapy)
revise antibiotics when C&S known
anti-convulsants (1-2 yr)
follow up CT is critical (do weekly initially, more frequent if condition deteriorates)
Prognosis
mortality with appropriate therapy ~10%, permanent deficits in ~50%