Brain MRI Basics: Understanding Common Neurological Findings

When your doctor orders a brain MRI, it’s not just a scan-it’s a window into what’s happening inside your brain. Unlike X-rays or CT scans, MRI doesn’t use radiation. Instead, it uses powerful magnets and radio waves to create detailed pictures of brain tissue. This makes it the most trusted tool for spotting problems like strokes, tumors, multiple sclerosis, and even early signs of dementia. But what do those images actually show? And how do doctors tell the difference between normal aging and something serious?

What Brain MRI Actually Shows

A brain MRI doesn’t just give you a picture-it gives you multiple pictures, each highlighting different things. These are called sequences, and each one tells a different story. The three most important ones are T1-weighted, T2-weighted, and FLAIR.

T1-weighted images are like a high-resolution anatomy map. Fat and certain types of tissue show up bright white. Cerebrospinal fluid (CSF), which fills the spaces around your brain, looks dark. This sequence is great for seeing the shape of your brain, the size of your ventricles, and whether there’s any swelling or mass pushing things out of place.

T2-weighted images flip the script. Water becomes bright. That means anything with extra fluid-like swelling from an injury, infection, or inflammation-lights up like a beacon. But here’s the catch: CSF also looks bright on T2. That’s why it can be tricky. A dark spot on T1 might be a bleed. A bright spot on T2 might be a tumor. Or it might just be normal fluid.

That’s where FLAIR comes in. FLAIR stands for Fluid-Attenuated Inversion Recovery. It’s a special version of T2 that turns CSF dark again, while keeping abnormal fluid (like lesions from multiple sclerosis) bright. This is critical. Without FLAIR, you might mistake normal fluid-filled spaces for disease. With it, you can clearly see those telltale white spots around the ventricles that signal MS.

Common Findings and What They Mean

Not every bright spot is a disaster. Many findings are normal-or at least common with age. Here are the most frequent things radiologists see and what they mean.

White matter hyperintensities-those small bright spots on T2 and FLAIR-are seen in nearly 90% of people over 70. They’re often linked to tiny blood vessel changes from high blood pressure or aging. They’re called leukoaraiosis in medical terms. While they don’t always cause symptoms, they do raise the risk of stroke and cognitive decline over time.

Lacunar infarcts are tiny strokes, usually less than 5mm, that happen deep in the brain-often in the basal ganglia or thalamus. They’re caused by blockages in small arteries. You might not feel them. Many people live with them without knowing. But if you have several, it’s a sign your brain’s small vessels are under stress.

Multiple sclerosis plaques look different. They’re often oval, located near the ventricles, and run perpendicular to the brain’s surface. They’re called Dawson’s fingers. Unlike age-related spots, they tend to appear in multiple areas and change over time. FLAIR makes them stand out. If you’re under 50 and have these, MS is a real possibility.

Acute stroke shows up fast on a special sequence called DWI (diffusion-weighted imaging). Within minutes of a stroke, water movement in brain cells gets restricted. DWI picks this up immediately. That’s why MRI is now the gold standard for stroke diagnosis. CT can miss early strokes-MRI doesn’t.

Tumors can be tricky. Some look like swelling. Others enhance with contrast dye. A meningioma, for example, often hugs the skull and lights up brightly after contrast. A glioma might spread into brain tissue without a clear border. Size, location, and how it reacts to contrast help doctors tell them apart.

Microbleeds are tiny leaks from fragile blood vessels. They show up as dark dots on SWI (susceptibility-weighted imaging) or gradient echo sequences. They’re common in older adults with high blood pressure or amyloid angiopathy. Finding more than five can raise concern for future bleeding risk.

Why MRI Beats CT for Neurological Problems

CT scans are fast. They’re great for trauma-like a head injury after a fall. But when it comes to neurological conditions, CT is like looking at a blurry photo. MRI is like zooming in with a 4K lens.

Here’s why:

• CT can’t see small lesions in the brainstem or cerebellum well. Bone blocks the view. MRI sees right through it.
• CT misses early strokes. MRI catches them in under 30 minutes.
• CT can’t distinguish between old and new MS plaques. MRI can.
• CT exposes you to radiation. MRI doesn’t. That’s why it’s preferred for kids and for people who need repeated scans.

But MRI isn’t perfect. It takes longer-30 to 45 minutes. You have to lie still. It’s noisy. And if you have a pacemaker, certain metal implants, or severe claustrophobia, you might not be able to have one. In emergencies, CT still wins because speed saves lives.

What MRI Can’t Tell You

Even with all its power, MRI doesn’t give you the full picture. A bright spot on FLAIR doesn’t tell you if it’s causing symptoms. It doesn’t tell you if it’s getting worse. It doesn’t tell you if it’s related to your headaches or memory lapses.

That’s why doctors don’t just look at images. They combine MRI findings with your symptoms, your medical history, and sometimes other tests-like spinal fluid analysis or blood work.

For example, a 45-year-old with headaches and a single small white matter lesion? Probably nothing. But if that same person has numbness in their legs, vision changes, and bladder issues? That changes everything.

And here’s something most people don’t realize: MRI finds incidental findings in up to 10% of scans done for headaches with no neurological signs. Most are harmless-like a tiny cyst or an old silent stroke. But they can cause anxiety, extra tests, and even unnecessary treatments. That’s why the American College of Radiology says MRI isn’t usually needed for simple migraines without warning signs.

How Radiologists Read a Brain MRI

Reading a brain MRI isn’t random. It’s a step-by-step process.

First, they check the midline. Is the brain centered? Is the third ventricle too wide? That could mean pressure or atrophy.

Then they look at the ventricles. Are they enlarged? That might be normal aging-or early dementia.

Next, they move to the deep structures: thalamus, basal ganglia, brainstem. Are there small bright spots? That’s where lacunar strokes hide.

Then the lobes: frontal, parietal, temporal, occipital. Are there abnormal signals? Is one side swollen? Temporal lobe lesions could mean herpes encephalitis. Parietal-occipital changes might point to posterior reversible encephalopathy syndrome (PRES), often linked to high blood pressure or pregnancy.

Finally, they check the cerebellopontine angle-the space between the cerebellum and brainstem. That’s where small tumors like vestibular schwannomas hide. They’re rare, but MRI catches them as small as 2mm. Miss them on CT? Almost guaranteed.

And they always compare sequences. A lesion that’s bright on T2 and FLAIR but dark on T1? Likely fluid-filled. Bright on T1 too? Could be fat, blood, or contrast dye.

What’s New in Brain MRI

Technology is moving fast. While most hospitals use 1.5T or 3.0T machines, some academic centers now have 7.0T scanners. These show brain layers so clearly, you can see individual cortical bands. It’s still research-only-but it’s changing how we understand brain diseases.

Artificial intelligence is helping too. New software can cut scan time in half without losing detail. It can automatically detect MS plaques, measure brain volume changes over time, and even predict which patients are at higher risk of dementia based on subtle patterns.

Quantitative MRI is another big leap. Instead of just saying “there’s a lesion,” it measures things like water content, blood flow, or myelin levels. These numbers can track disease progression more accurately than just looking at pictures.

And while MRI is still expensive-ranging from $1,200 to $3,500 in the U.S.-it’s becoming more accessible. In South Africa, public hospitals are slowly upgrading, and private clinics are offering more affordable packages. Still, access remains uneven, especially in rural areas.

What You Should Know Before Your Scan

If you’re scheduled for a brain MRI, here’s what matters:

• You’ll need to remove all metal-jewelry, piercings, even some makeup with metallic particles.
• Let them know if you have implants, pacemakers, or metal fragments (especially from old injuries).
• It’s loud. You’ll get earplugs or headphones.
• You have to lie still. Even a little movement blurs the images.
• Contrast dye isn’t always needed. It’s only used if the doctor suspects a tumor, infection, or inflammation.
• The scan takes 30-45 minutes. Bring something to help you relax.

And remember: a brain MRI doesn’t give you a diagnosis. It gives you clues. Your doctor puts those clues together with everything else to make sense of them.