Intracranial mass effect (summary)

This is a basic article for medical students and other non-radiologists

Intracranial mass effect describes what happens around a tumor in the brain. It is important to make the distinction between an abnormality that causes mass effect and compresses adjacent structures, and one that does not. Most tumors will cause mass effect on surrounding structures and in turn cause midline shift or hydrocephalus.

Reference article

This is a summary article; there is no parent article on this topic.


  • pathophysiology
    • the skull is a fixed volume and cannot increase in size
    • a lesion within the skull will compress and/or displace adjacent structures
    • mass effect may be caused by:
      • tumors
      • cerebral abscess
      • infarction and associated edema
      • hemorrhage


CT head | MRI brain​

  • role of imaging
    • quantify the degree of mass effect
    • what is the likely cause?
    • are any complications of mass effect, e.g hydrocephalus?
  • radiographic features
    • structures are pushed away from the mass lesion
    • compression of fluid-filled structures may result in obstruction
      • the 4th ventricle could be compressed by a tumor
      • obstruction of CSF flow results in increased pressure proximally
      • lateral and 3rd ventricular dilatation seen as hydrocephalus
Medical student radiology curriculum