Cerebral Abscess

Cerebral abscess formation: a brain abscess is a severe focal infection of the brain; the process is similar in any abscess except there is gliosis instead of fibrosis in the brain…

1. Infection / stimuli (esp. pyogenic organism) producing acute inflammation of the brain parenchyma (cerebritis).

2. Inflammatory stimuli persists (host and virulent factors)  increased inflammatory infiltrate and accumulation of necrotic material (formation of pus)

3. Subsequent encapsulated area and gliosis  abscess formation

Note: an abscess is a localised collection of pus within a cavity

Morphology:

There is a central region of liquefactive necrosis and a fibrous capsule surrounded by reactive gliosis. Brain abscess is often associated with marked cerebral oedema.

Symptoms:

• Fever is typically low grade

• Altered mental status ranges from subtle personality changes, to drowsiness, to full-blown coma

• Nuchal rigidity occurs in about 25% of cases

• Focal neurological signs can signal increasing cerebral oedema around the abscess

• Seizures are typically grand mal

• Papilledema indicates the disease process is well advance

Mortality/Morbidity:

• The mortality rate has dropped to approximately 10%.

• Morbidity in survivors is generally due to residual focal defects, increased incidence of seizures due to scar tissue foci, or neuropsychiatric changes.

Epidemiology:

• Sex: Brain abscesses develop in men twice as often as in women.

• Age: Incidence peaks in the fourth decade of life.

Causes: usually secondary to a focus of infection outside of the CNS…

The majority of brain abscesses originally stemmed from nasopharyngeal infections such as otitis media, mastoiditis, and sinusitis. Because of improved antibiotic therapy, today these sources account for approximately 40% of cases.

Haematogenous spread from remote primary infection accounts for nearly 30% of cases. Of these, pulmonary infections traditionally have been cited as frequent sources, though dental infections are increasingly the primary site.

Direct seeding from trauma or neurosurgical procedure causes 10% of cases.

In the past, approximately 20% of cases were considered to be either idiopathic or of undetermined origin. In all of these cases, etiologic organisms were overwhelmingly bacterial, including aerobic (e.g. Streptococcus milleri, Streptococcus viridans, Staphylococcus aureus, beta-hemolytic Streptococci) and anaerobic species (e.g. Bacteroides species, anaerobic Streptococci).

An increasingly prevalent cause is opportunistic infection by formerly exotic fungal and protozoan organisms, which follow such immunosuppressive diseases as HIV and chronic tuberculosis (TB). Such organisms as Toxoplasma gondii and Nocardia, Aspergillus, and Candida species now constitute the most common sources of brain abscesses in some inner-city areas in AIDS-endemic zones.

Category: Medicine Notes , Pathology Notes