Vols. Videos


Last Updated: October 1, 2018

Empyema is a pyogenic intracranial infection of an extra-axial space. It probably occurs secondary to retrograde thrombophlebitis of emissary veins adjacent to the site of infection. In infants, empyemas occur more commonly as a complication of bacterial meningitis. In adults, empyemas can be seen after craniotomy, in the setting of severe sinusitis or mastoiditis, or after trauma. It is important to differentiate simple (reactive) effusions from infected effusions, because empyemas, especially if subdural, are a neurosurgical emergency.

Imaging Features

Empyema presents as a rim-enhancing fluid collection with associated meningeal inflammation and possible cerebritis/abscess. Findings on CT and MR parallel each other.

  • CT:
    • Non-contrast: Intermediate density extra-axial fluid collection that is slightly more dense than CSF, but not as dense as blood products.
    • Contrast-enhanced: Rim-enhancing collection superficial to a cerebral or cerebellar hemisphere
      • If subdural—crescent-shaped, confined by dural reflections, and does not cross midline
      • If epidural—lens-shaped, crosses midline, and t...