- Clinical science
A brain abscess is a focal, suppurative lesion that may occur in one or more regions of the brain. It may be caused by the direct spread of sinus, ear, and/or dental infections, inoculation of pathogens following open skull fractures, and/or hematogenous spread from infective foci. During the course of the disease, the infected brain tissue softens and is subsequently encapsulated by granulation tissue. Clinical manifestations include headache, fever, neurological deficits, seizures, nausea, vomiting, and other features of raised intracranial pressure. Given these clinical findings, the main differential diagnosis is primary or metastatic brain tumor. Contrast CT reveals an intraparenchymal lesion with a hypodense center and peripheral ring enhancement. Treatment of brain abscesses involves surgical drainage of the abscess followed by systemic antibiotic therapy.
- Usually an otogenic, sinus, oral, or meningeal (e.g., meningitis) source of infection
- Other sources: septic foci , open skull fractures, and/or neurosurgical procedures
- Viridans streptococci (∼50% of cases), often secondary to sinusitis
- Staphylococcus aureus (10–15% of cases)
- Coagulase-negative staphylococci (∼10% of cases)
- Obligate anaerobes (e.g., Bacteroides species; 15–40% of cases)
- Gram-negative aerobic bacteria (e.g., Enterobacteria, Pseudomonas species; 15–30% of cases)
- Parasites (e.g., neurocysticercosis in patients from Latin America, Sub-Saharan Africa, and Asia)
- In immunocompromised states: Toxoplasma, Aspergillus, Candida, Mucormycosis (also known as Zygomycosis), Cryptococcus
- Entry of pathogens via contiguous spread, direct inoculation, or hematogenous spread
Clinical features depend on the size and location of the lesion.
- Dull persistent headache
- (e.g., vomiting, papilledema, altered mental status)
- Focal neurological deficits
- Generalized or focal seizures (∼ 30% of cases)
- Laboratory tests
- CT/MRI: : intraparenchymal lesions with a central hypodense (necrotic) area and peripheral ring enhancement
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. Infections are often multibacterial; tailoring of antibiotic therapy to specific bacterial sensitivities is especially important given the length of treatment.
- Subacute hemorrhage and/or infarction
The differential diagnoses listed here are not exhaustive.
- Early surgical drainage and biopsy of the abscess
Antibiotic therapy for 6–8 weeks (usually IV ;)
- If brain abscess < 2.5 cm, history of symptoms < 1 week, and no signs of ICP → antibiotic therapy without surgical drainage may be attempted
- In all other cases → begin immediately after abscess biopsy/drainage
- Initial empirical therapy (e.g., third-generation cephalosporin + metronidazole ± vancomycin)
- Specific antibiotics may be used once the causative organisms and their antibiotic sensitivities are known.
- Seizure prophylaxis (e.g., anticonvulsants)
- If treated early: high survival rates and low rates of residual neurological sequelae
- Multiple, deep, ruptured; , or inadequately treated abscesses have a poor prognosis.