脳膿瘍1:はじめに

A brain abscess is a localized, pus-filled mass within brain tissue resulting from infection and inflammation. It develops when pathogens like Staphylococcus aureus breach the blood-brain barrier and infect brain tissue, triggering tissue necrosis. The abscess progresses through stages of cerebritis followed by capsule formation, reflecting the body's inflammatory response and eventual encapsulation of the infection.

Pathogens reach the brain through multiple routes: contiguous spread from ear, sinus, or dental infections; hematogenous spread via bloodstream from lung or heart infections; or direct inoculation through penetrating head trauma, neurosurgical procedures, or compound skull fractures. Infection can also spread from nearby infected tissue, bypassing normal protective barriers.

Common symptoms include persistent headache, fever, and focal neurological deficits such as visual field defects. Additional signs include nausea, vomiting, seizures, and papilledema from raised intracranial pressure. In severe cases, rapid mental deterioration may occur, and without prompt treatment, the infection can be fatal.

As the abscess enlarges, it exerts pressure on nearby brain structures, functioning as a space-occupying lesion that disrupts normal brain activity. The location determines specific neurological effects: supratentorial lesions may cause hemiparesis or speech issues, while infratentorial lesions may produce ataxia or cranial nerve deficits.

Causative organisms vary with infection source and host factors, often involving polymicrobial infections including streptococci, Staphylococcus aureus, and Gram-negative bacilli. Fungi or parasites may occur in immunocompromised individuals. The specific pathogen profile depends on whether infection spreads contiguously from local sources or hematogenously from systemic infections.

Risk increases in individuals with chronic ear or sinus infections, congenital heart disease, immunosuppression, or uncontrolled systemic infections. Conditions like HIV/AIDS, organ transplantation, or steroid use significantly alter pathogen profiles and disease progression, making these populations particularly vulnerable to brain abscess development.

Diagnosis relies primarily on contrast MRI, which is the most sensitive imaging modality; lumbar puncture is avoided due to herniation risk. Treatment includes intravenous antibiotics and often surgical drainage. Corticosteroids may reduce cerebral edema in severe cases, and outcomes have improved with modern care, though delayed treatment may result in lasting neurological deficits.