Pyogenic inflammation of the brain leading to cerebral abscess may result from:

• direct spread from an adjacent focus of infection such as sinusitis, otitis or dental infections. The infection usually involve the adjacent part of the brain. As such, frontal sinusitis affects the frontal lobe while otitis spread to the temporal lobe. They are usually single and superficial and are therefore amenable to treatment and have a favorable prognosis

• haematogenous spread from a known septic site or occult focus. These are often multiple, deeply seated, and relatively poorly encapsulated when first diagnosed, and consequently have a less favorable prognosis. They tend to be distributed proportionately to regional blood flow, which makes the middle cerebral artery territory the most common location. The initial source of infection is often found within the chest in chronic pyogenic lung diseases, such as pneumonia, lung abscesses, bronchiectasis, and empyema. Other causes include skin pustules, osteomyelitis, pelvic and intra-abdominal infections, and invasive medical interventions. Patients with right-to-left vascular shunts, including those with congenital cyanotic heart disease and those with pulmonary arteriovenous malformations, are predisposed to cerebral abscess. Congenital cyanotic heart disease is the most common underlying condition in children. Tetralogy of Fallot and transposition of the great vessels are the most common culprits.

• trauma causing a penetrating wound, especially with retained objects such as bone fragments. The presence of chronic cerebrospinal fluid fistula is also associated with the development of intra-parenchymal suppuration.

It is important to note that immunosuppression, caused by e.g diabetes mellitus and AIDS, is an important risk factor for the development of cerebral abscess. Atypical organisms are especially common in immuno-compromised individuals.

Despite the foregoing, somes cases of brain abscess do not have known predisposing factors and appear to develop de novo.

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