What it means
The skull is a closed box, so anything that takes up extra room inside it presses on the brain. Mass effect is the term for that pressure. Signs include brain tissue pushed aside, fluid spaces squeezed narrower, or the brain shifting from its central position. A tumor, bleeding, swelling, a pocket of infection or a large stroke can all cause it. Elsewhere in the body, it describes a lump pressing on nearby organs.
When it matters
"No mass effect" is a common and reassuring phrase in brain reports. When mass effect is present, its degree matters. Mild local mass effect from a slow-growing lump may cause no symptoms and is sometimes simply watched. Marked mass effect, such as a large midline shift, is treated as urgent, because the brain has little room to spare. The report usually says how much and where.
Questions to ask your doctor
- What is causing the mass effect, and how much pressure is there?
- Is there any midline shift, and does it explain my symptoms?
- Does this need urgent treatment, or can it be watched with repeat scans?
