Mass Effect
Mass effect describes how a lesion is pushing on nearby structures — bulging into them, displacing them, or compressing surrounding tissue.
When to get help quickly: Significant mass effect — especially in the brain, with midline shift, herniation, or new neurological symptoms — is a neurosurgical emergency.
Common symptoms
Mass effect is a finding on a scan; the symptoms depend on what is being compressed (headache and nausea in the brain, swallowing problems near the throat, breathing issues near the airway).
When imaging helps
Imaging shows the size of the lesion, what it is pressing on, how much displacement is present, and whether it is causing additional changes such as midline shift or hydrocephalus.
What radiology does
CT and MRI both show mass effect; MRI gives more detail about how the lesion relates to surrounding soft tissue.
What usually happens next
Treatment targets the underlying lesion (tumour, abscess, bleed, oedema) and may include steroids to reduce swelling, surgical decompression, or other specific therapy.
Seen this on your report?
Your doctor or the radiologist who wrote it can tell you what it means for you.