Brain abscess and empyema
- Lesion
Bacteria can reach the brain from sinuses, ears, teeth, the blood or wounds and form a pocket of pus walled off by a capsule.
What it is
Focal suppurative infections are collections of pus inside or around the brain. A brain abscess forms when bacteria seed the parenchyma by direct spread (sinusitis, otitis, mastoiditis, dental infection), through the blood (endocarditis, lung abscess, right-to-left shunts) or after trauma or surgery. Infection in the potential spaces under the dura (empyema) or outside it (extradural abscess) usually spreads from the skull or sinuses. All of them act as expanding masses.
Structure
- Early (cerebritis): poorly defined area of necrosis, neutrophils and edema.
- Mature abscess: central pus, a wall of granulation tissue with new vessels, and a fibrous capsule thinner on the ventricular side, where rupture is most likely.
- Subdural empyema: pus between dura and arachnoid, sometimes with venous thrombosis of the cortex below.
- Extradural abscess: pus between bone and dura, often with osteomyelitis; in the spine it compresses the cord.
Focal suppurative CNS infections
| Lesion | Space | Usual source | Danger |
|---|---|---|---|
| Brain abscess | Brain parenchyma | Sinus, ear, dental, endocarditis, trauma | Mass effect, rupture into ventricles |
| Subdural empyema | Under the dura | Sinusitis, mastoiditis | Cortical vein thrombosis, seizures |
| Cranial extradural abscess | Between skull and dura | Osteomyelitis, sinusitis, surgery | Spread inward |
| Spinal epidural abscess | Spinal epidural space | Bacteremia, vertebral osteomyelitis, procedures | Cord compression |
Clinical notes
- Headache, fever (not always), focal deficits and seizures; a fast-growing mass with edema.
- In AIDS, ring lesions are more often toxoplasmosis or lymphoma than bacterial abscess.
Test yourself
Think of the answer, then tap the question to see it.
Why does a brain abscess tend to rupture into the ventricle?
Its capsule is thinner on the ventricular side, where blood supply and fibroblast response are poorer.
Which lobe is usually involved when an abscess follows otitis media or mastoiditis?
The temporal lobe, or the cerebellum.
What is the classic imaging appearance of a mature brain abscess?
A ring-enhancing lesion with a smooth wall and surrounding vasogenic edema.
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Brain abscess: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Spinal Epidural Abscess (StatPearls (NCBI Bookshelf), 2026).
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Representative model, for educational purposes only.