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IA. Mass lesions - Introductory concepts

A. Intracranial Space-occupying Expanding Mass Lesions

1. General Considerations

Since the brain is enclosed in a rigid cranium, the free space to expand is minimal.  When the mass of brain intracranial contents increases in the presence of disease, intracranial pressure (ICP) increases. When ICP exceeds a critical point, displacements and herniations occur. The nature of herniation is determined by the location of the lesion.

Intracranial pressure is usually estimated by measuring CSF pressure through lumbar puncture. The normal value is < 200 mm water.  CSF pressure depends on cerebral blood volume (varies with systole/diastole and respiration), volume of brain tissue and volume of CSF.

2. Compensatory Mechanisms

  • Reduction in cerebrospinal fluid (CSF) volume
  • Reduction in intracerebral blood volume
  • Loss of brain tissue, e.g. necrosis and atrophy