Brain abscess pathophysiology
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Brain abscesses are usually polymicrobial in nature. Swelling and irritation (inflammation) develop in response to this infection. Infected brain cells, white blood cells, live and dead bacteria, and fungi collect in an area of the brain. Tissue forms around this area and creates a mass. While this immune response can protect the brain by isolating the infection, it can also do more harm than good. The brain swells. Because the skull cannot expand, the mass may put pressure on delicate brain tissue. Infected material can block the blood vessels of the brain.
Pathophysiology
Pathogenesis
The location of the primary lesion may be suggested by the location of the abscess. Roughly 25% result from hematogenous seeding from extra-cranial infection. Penetrating trauma accounts for nearly 10% of cases. 20-30% of cases are iodiopathic, and no obvious focus can be identified. Common locations include:
- Infections of the middle ear result in lesions in the middle
- Approximately 47% of cases arise from a contiguous infection, most commonly in the middle ear, the paranasal sinuses and teeth.
- Posterior cranial fossae[1]
- Congenital heart disease with right-to-left shunts often result in abscesses in the distribution of the middle cerebral artery[2][3]
- Infection of the Frontal and Ethmoid sinuses usually results in collection in the subdural sinuses.
The most common organism recovered from cultures is the bacterium Streptococcus.
A wide variety of other bacteria may cause brain abscess. These include:
- (Proteus, Pseudomonas, Pneumococcus, Meningococcus, Haemophilus)
- Fungi
- Fungi and parasites are especially associated with immunocompromised patients.
- Parasites
Organisms that are most frequently-associated with brain abscess in patients with AIDS are Mycobacterium tuberculosis, Toxoplasma gondii and Cryptococcus neoformans, though in infection with the latter organism, symptoms of meningitis generally predominate.
Bacterial abscesses rarely (if ever) arise de novo within the brain. There is almost always a primary lesion elsewhere in the body that must be sought assiduously, because failure to treat the primary lesion will result in relapse. In cases of trauma, for example in compound skull fractures where fragments of bone are pushed into the substance of the brain, the cause of the abscess is obvious. Similarly, bullets and other foreign bodies may become sources of infection if left in place.
Brain abscesses usually start as a focal area of cerebritis that eventually develops into a collection of puss, surrounded by a well-vascularized capsule.
- In general, the brain is relatively resistant to infection due to the presence of the abundant blood supply, and the relatively impermeable blood-brain barrier.
- Although underlying pathology (tumor, blood etc.) can sometimes be a nidus for infection, the majority of cases occur in a previously healthy brain.
- Experimental models have identified four stages for abscess formation:
- Early cerebritis (days 1 – 3): focal inflammation and edema.
- Late cerebritis (d 4 – 9): development of a necrotic center.
- Early capsular (d 10 – 14): formation of a well-vascularized, ring-enhancing capsule with peripheral gliosis and/or fibrosis.
- Late capsular: (after 2w): formation of a well-formed fibrous capsule.
- The location of the abscess obviously depends on the source of infection, as does the specific microbial flora.
References
- ↑ Macewan W (1893). Pyogenic Infective Diseases of the Brain and Spinal Cord. Glasgow: James Maclehose and Sons.
- ↑ Ingraham FD, Matson DD (1954). Neurosurgery of Infancy andChildhood. Springfield, Ill: Charles C Thomas. Unknown parameter
|paes=ignored (help) - ↑ Raimondi AJ, Matsumoto S, Miller RA (1965). "Brain abscess in children with congenital heart disease". J Neurosurg. 23: 588&ndash, 95.