Medically reviewed by Edward Tavel, MD, Medical Director · Last reviewed 22 August 2026
A brain tumor is a growth of abnormal cells within the brain or the tissues immediately surrounding it. Tumors are described in two broad ways. A primary brain tumor begins in the brain itself, while a metastatic tumor has spread to the brain from a cancer elsewhere in the body — in adults, metastatic tumors are actually the more common of the two. Tumors are also described as benign or malignant. A benign tumor grows slowly and does not invade surrounding tissue, but because the skull is a fixed space, even a benign growth can cause symptoms by pressing on nearby structures. Meningiomas, which arise from the membranes covering the brain, are among the most frequently encountered benign types and are often found by chance.
Symptoms depend far more on where a tumor sits than on how large it is. A small growth in a critical area can cause noticeable effects while a larger one elsewhere causes very few. Common signs include headaches that change in pattern or are worse in the morning, new seizures in an adult, weakness or numbness on one side, changes in vision or speech, balance difficulty, persistent nausea, or shifts in memory, concentration, or personality that others notice first. Most headaches are not caused by tumors, and these symptoms have many ordinary explanations — but a new seizure, a progressive neurological change, or a headache that is genuinely different from your usual pattern should be assessed by a physician. Evaluation typically involves a neurological examination followed by imaging, and a tissue diagnosis where treatment decisions require one.
MRI is the primary imaging test for the brain, because it distinguishes between soft tissues far more clearly than other methods and can show the relationship between a growth and the structures around it. Radiologists assess size, location, borders, effect on surrounding tissue, and how the area behaves across different MRI sequences. On a preventive whole-body or brain scan, the great majority of brain findings are benign or of no consequence, and small meningiomas or cysts are sometimes identified in people with no symptoms at all. Such findings are usually managed with observation rather than intervention. If you are considering imaging, you may find it useful to read about gliomas and how they appear on MRI, the conditions a whole-body scan can detect, and how we approach incidental findings on an MRI.
Frequently asked questions
Are most brain tumors cancerous?
No. A large share of primary brain tumors are benign, meningiomas being a common example. Benign does not always mean untreated, since location can still cause symptoms, but it does mean the growth is not invading tissue or spreading.
Do headaches usually mean a brain tumor?
Very rarely. Headaches are extremely common and tumors are not. What matters more is change: a headache unlike your usual pattern, one that wakes you or is worst on waking, or one accompanied by neurological symptoms warrants assessment.
Can an MRI tell whether a tumor is benign or malignant?
MRI can suggest which is more likely from appearance, borders, and behaviour across sequences, and some tumors have characteristic patterns. A definitive answer generally requires tissue examination, so imaging guides the next step rather than concluding it.
What happens if a scan finds something unexpected?
Most incidental brain findings are benign and need only observation. The usual next step is a discussion with your physician and, where appropriate, a repeat scan after an interval to see whether anything has changed.
Does a clear brain MRI rule out a tumor permanently?
It describes the brain on the day of the scan. A clear result is reassuring about that moment, but it is not a guarantee about the future, and new or progressive symptoms should always be evaluated regardless of a previous normal scan.
Sources
A whole-body MRI at MRI Wellness looks at the brain, spine, chest, abdomen and pelvis in a single session, without radiation or contrast dye. No referral is needed.
