Intraparenchymal brain abscess accounts for approximately 2% of intracranial masses.183 Etiologies, in order of frequency, are:181

• metastatic spread from infection elsewhere (e.g., pneumonia, endocarditis)
• direct extension from cranial and parameningeal infection (e.g., paranasal sinusitis, mastoiditis, osteomyelitis)
• unknown source
• direct seeding via trauma or neurosurgical procedure
• history of congenital heart disease

The most common pathogens are bacterial, specifically Streptococci, Staphylococci, Bacteroides, Proteus, and anaerobes. Actinomyces, Nocardia, and Candida are also common abscess-generating pathogens. Infection is often polymicrobial.181

The clinical course is consistent with that of an expanding intracranial mass lesion. Seizures are the presenting manifestation in at least one-third of cases.181,183 Although headache and fever are the most frequent initial symptoms, common signs of infection can be missing. For example, the white blood cell count is normal in 20% of cases.181,183

Diagnosis

Neuroimaging usually confirms the diagnosis by revealing a typically ring-enhancing lesion on contrast CT or MRI.181,184 EEG can demonstrate a high-voltage slow wave over the affected brain region.181,183 Lumbar puncture is usually contraindicated because of mass-related increased intracranial pressure.

Treatment

Antibiotics can be used alone or in combination with surgical drainage.185 The threshold for neurosurgical evacuation is lowered by the presence of significant mass effect or location near a ventricular surface. (Rupture into the ventricular system may cause florid ventriculitis or meningitis.)185

Antibiotic selection is based on knowledge of the likely infection source. Antibiotics targeting a broad spectrum of organisms (including anaerobes) often are used, such as penicillin plus chloramphenicol or metronidazole.181,183 Serial neuroimaging is usually performed to assess treatment response.186

Seizure management is important, especially given a context of intracranial pressure complications. Epilepsy is a frequent long-term sequela, secondary to residual epileptogenic encephalomalacia.181 Anticonvulsant therapy (e.g., phenytoin) is often maintained for at least 1 year after abscess treatment.181

Adapted from: Goldstein MA and Harden CL. Infectious states. In: Ettinger AB and Devinsky O, eds. Managing epilepsy and co-existing disorders. Boston: Butterworth-Heinemann; 2002;83-133.
With permission from Elsevier (www.elsevier.com).
Reviewed and revised March 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.