Acute CT Brain
Intracranial masses

Key points

  • Intracranial masses can be intra or extra-axial
  • Single intra-axial lesions are usually primary malignant lesions
  • Multiple intra-axial lesions are usually metastatic
  • Meningiomas - the commonest extra-axial masses - are located in close proximity to a meningeal surface
  • Cerebral abscess is an important differential diagnosis of a ring enhancing mass

Intracranial masses are classified either as intra-axial lesions (in the brain) or extra-axial lesions (outside the brain). The distinction is not always easy to determine.

Intra-axial lesions

Intra-axial lesions are most commonly neoplastic and malignant rather than benign. In general, a single intra-axial lesion which enhances post-contrast is most likely to be a primary malignant mass (glioma), whereas multiple intra-axial lesions are usually metastatic.

Glioma - CT brain/pre-contrast image

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Glioma - CT brain/pre-contrast image

  • This patient presented with clinical features similar to an acute stoke and a recent history of worsening postural headaches
  • A large irregular-shaped area of low density is seen in the right hemisphere
  • Mass effect is present: effacement of the sulci, lateral ventricle and basal cisterns

Glioma - CT brain/post-contrast image

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Glioma - CT brain/post-contrast image

  • (Same patient as image above)
  • A post-contrast CT of the brain was performed
  • There is 'ring-enhancement' of an irregular-shaped mass
  • Central low density is due to necrosis
  • Surrounding low density is due to oedema
  • Note: Cerebral abscesses have similar enhancement characteristics and should be considered as a differential diagnosis of a ring enhancing lesion

Cerebral metastases - CT brain

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Cerebral metastases - CT brain

  • Multiple lesions were seen on both sides of the brain in this patient who had a known diagnosis of lung cancer
  • The post-contrast image (roll over image) shows ring enhancement of the lesions

Extra-axial lesions

Meningiomas are the most common extra-axial mass. Although benign, they may grow very large and can be surrounded by a large area of adjacent cerebral oedema, often appearing to be intra-axial on initial assessment.

Characteristics of meningiomas include a smooth edge, a rounded shape, central calcification, and bright enhancement of the whole lesion post-contrast. Meningiomas arise from the meninges, with which they remain in contact, and often have a 'dural tail' which tapers from the mass to a point on the surface of the meninges.

Meningioma - CT brain/post contrast image

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Meningioma - CT brain/post contrast image

  • A large mass enhances brightly following administration of intravenous contrast
  • A large area of oedema is seen adjacent to the mass
  • The mass makes broad contact with the meninges (the falx in this case)
  • There is a 'dural tail' - tapering of the mass to a point on the meningeal surface