The most common sites are the frontal and temporal lobes. These are followed by abscesses in the frontoparietal, parietal, cerebellar, and occipital lobes, in descending frequency. Thalamic abscesses are rare. Formation of the abscess begins with entry of a microorganism into the brain, which produces an initial area of focal cerebritis leading to softening, edema, hyperemia and petechial hemorrhage. Fibroblasts from the capillaries adjacent to the focal cerebritis deposit collagen fibers to contain and encapsulate the purulent focus.
Encapsulation usually takes two weeks.
Whenever symptoms and signs of intracranial disease develop in a patient with infection of the middle ear, mastoid, sinuses, soft tissue of the face, orbit and scalp, brain abscess should be considered. The infection is most often subacute or chronic and spreads by infected veins or less commonly by osteomyelitis. Congenital lesions including dermal sinuses and various forms of ruptured encephalocele may provide direct microorganisms to brain tissue. Hematogenous brain abscess may be replacing contiguous foci as the primary cause of brain abscess. These lesions occur most often with infections of the chest or as a result of cyanotic congenital heart disease.