An abscess arises from septic emboli or direct exposure of the brain to outside organisms through head trauma or erosion of an infection through the bone as in sinusitis and mastoiditis.
Both bacteria and fungi can cause abscesses.
In parenchymal abscesses, an area of microvascular damage due to a septic embolus causes a small area of necrosis due to the influx of neutrophils and bacteria or fungi into the area.
The surrounding tissue begins to form inflammatory granulation tissue about the area of necrosis in a few days.
Within a week or two if the necrotic area does not spread a collagenous capsule infiltrated by neutrophils, lymphocytes, plasma cells and macrophages surrounds the necrotic center with an astrocytic border and chronic inflammation.
This is one of the two lesions in the brain that is surrounded by connective tissue, most brain lesions are surrounded by astrocytic fibers only.,
Brain abscesses are seen most often in patients who have lung abcesses or bronchiectasis, head trauma or, less often, with sinusitis or mastoiditis.
Abscesses are seen also in patients with bacterial endocarditis or intracardiac shunts.
It is the second most common intracranial infection and can occur in the epidural and subdural space or intraparenchymally.
Abscesses can be seen at all ages.
|General Gross Description|
Early on the abscess appears as an area of necrosis which is relatively circumscribed.
As time goes by, if the abscess does not spread producing a larger area of necrosis, it is surrounded by a firm capsule. This can rupture and cause a spreading cerebritis or rupture into a ventricle producing ventriculitis or meningitis.
|General Microscopic Description|
Microscopically, the abscess has a center full of necrotic debris, neutrophils, macrophages and organisms.
The second layer about this is made up of proliferating fibroblasts and capillaries with a more chronic inflammatory reaction.
The third layer is of reactive astrocytes with plump pink cytoplasm as well as chronic inflammatory cells such as lymphocytes and plasma cells.
Poirer J et.al. Manual of basic neuropathology. Philadelphia: Saunders, 1990, pp. 105.
Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th ed. Philadelphia, W.B. Saunders, 1994, pp. 1316-1317.
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||Synopsis by: M.L. Grunnet M.D. (TX2000M41740)