BRAIN ABSCESS

A brain abscess begins as a localized area of cerebritis that develops into a collection of pus surrounded by a well-vascularized capsule. Brain abscesses are uncommon, with reported occurrence rates of 0.18% to 1.3% in large autopsy series. They most commonly result from contiguous septic foci, but hematogenous spread from a distant source and neurosurgical procedures or trauma are other risk factors. No predisposing factor can be found in approximately 20% of cases (Table 76.1).

The age distribution of patients with brain abscess varies with its cause. A brain abscess from an otogenic focus typically occurs in patients younger than 30 and shows a male predominance. Brain abscess secondary to sinusitis typically occurs in men in their second to third decade of life.

Pathogenesis

The location of a brain abscess is dependent on its predisposing cause. Abscess from a contiguous focus usually occurs in the cortical area of the brain near its causal site. The most common focus of contiguous infections are otitis or sinusitis. Infection from a contiguous site can either spread directly through intervening tissues, bone, and meninges or indirectly through retrograde thrombophlebitis of the diploic or emissary veins. An abscess may also result from an otogenic infection by spread through preexisting channels such as the internal auditory canal, cochlear, and vestibular aqueducts. The majority of otogenic brain abscesses are located in the temporal lobe, followed by the cerebellum. Approximately 90% of cerebellar abscesses are secondary to an otogenic infection. Brain abscesses due to sinusitis are almost always found in the frontal lobe.