Brain Abscess: Risk Factors, Symptoms & Treatment

INCIDENCE: Brain abscesses are rare. The greatest incidence is seen in patients between the ages of 20 and 40 years; men are affected twice as often as women.

PATHOGENESIS

1. Abscesses typically develop as a result of an external infection focus.

a) Brain abscesses arise from the middle ear, mastoid, and paranasal sinuses 40% of the time.

b) The hematogenous spread of bacteria from remote sites causes 30% of infections.

c) Thirty percent of brain abscesses have no clear cause.

2. The cerebrum becomes inflamed, an abscess forms, and then it becomes encapsulated. Three major complications can cause sudden deterioration: uncal or tonsillar herniation, spontaneous hemorrhage, and rupture of the abscess into the ventricular or subarachnoid space.

RISK FACTORS for brain abscess include AIDS, immunosuppression, and intravenous

drug abuse.

CLINICAL FEATURES: The clinical presentation may mimic that of a brain tumor, but the presentation of an abscess usually evolves more rapidly (e.g., within days to weeks). The classic presentation is one of headache, recent seizure, low-grade fever, and a focal neurologic deficit.

a) Headache is the most common symptom; it is present in 70% to 90% of affected patients.

b) Focal neurologic deficits are found in 75% of patients.

c) Seizures are found in 30% of patients; fever in 50% of patients.

DIFFERENTIAL DIAGNOSES include a tumor, encephalitis or meningitis, cerebrovascular accident, subarachnoid hemorrhage, migraine, and an extradural abscess.

EVALUATION: Cerebral inflammation develops into an abscess and then becomes encapsulated. Laboratory values are rarely helpful, although the WBC count is elevated in 30% of patients.

THERAPY: Surgical intervention and antibiotic treatment are part of definitive care.

1. Supportive therapy: If there are signs of increased intracranial pressure, the physician may need to elevate the bed 30 degrees, intubate the patient, and institute dexamethasone therapy (10 mg intravenously followed by 4 mg every 6 hours for adults; 0.6 mg/kg every 6 hours for children).

2. Antibiotic therapy: Drugs should be selected using susceptibility testing as a basis (see table below), and therapy should be continued for 4 to 6 weeks.

DISPOSITION: Patients with brain abscesses require hospital admission and immediate neurosurgical consultation.