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 strong magnets and radio waves to create incredibly detailed pictures of brain tissue. This makes it the most powerful tool doctors have 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

Brain MRI doesn’t just take a picture-it captures how water behaves in different tissues. That’s why it’s so good at showing subtle changes. Healthy brain tissue has a clear balance of gray matter (where nerve cells live) and white matter (the wiring connecting them). On a T1-weighted image, gray matter looks darker than white matter, like a photo negative. Fluids like cerebrospinal fluid (CSF) appear black. That’s normal.

But when something goes wrong, water behavior changes. Swelling from injury or inflammation makes tissue hold more water, which shows up bright on T2-weighted and FLAIR images. That’s why doctors rely on these sequences to find lesions-tiny areas of damage that might be invisible on a CT scan. For example, in multiple sclerosis, plaques form where the protective coating around nerves breaks down. These show up as bright spots near the ventricles, the fluid-filled spaces in the brain’s center.

One common mistake is confusing normal age-related changes with disease. Nearly 90% of people over 70 have small bright spots on their MRI in the white matter. These are often just tiny blood vessel changes from years of high blood pressure or aging-not signs of MS or dementia. The key is location and pattern. Lesions in the deep white matter near the ventricles? Likely benign. Lesions in the cortex, brainstem, or spinal cord? That’s a red flag.

The Five Key MRI Sequences You Need to Know

Not all MRI images are the same. Each sequence highlights different things. Here’s what matters most:

• T1-weighted: Best for anatomy. Fat and some blood products look bright. CSF is dark. Used to see brain structure, tumors, and bleeding after a few days.
• T2-weighted: Shows water. Swelling, tumors, and inflammation glow bright. CSF is also bright, which can make it hard to tell if a bright spot is fluid or damage.
• FLAIR: The game-changer. It turns CSF black but keeps lesions bright. This is how doctors spot MS plaques, small strokes, and infections hiding near fluid-filled spaces.
• Diffusion-weighted imaging (DWI): The fastest way to catch a stroke. Within minutes of a stroke, water can’t move normally in brain cells. DWI shows this as a bright spot. If it’s bright on DWI but dark on ADC (the companion map), it’s an acute stroke-time-sensitive and treatable.
• SWI or gradient echo: Picks up tiny amounts of blood. Great for spotting microbleeds from high blood pressure, trauma, or amyloid angiopathy. These are often invisible on other sequences.

Doctors don’t look at one image-they compare all five. A bright spot on T2 that’s also bright on FLAIR? Probably a lesion. A bright spot on T2 but dark on FLAIR? Likely just CSF. DWI changes everything if you’re thinking stroke.

Common Findings and What They Mean

Here are the most frequent findings-and what they really mean in practice:

• White matter hyperintensities: Bright spots in the white matter. In people under 50, they’re uncommon. In older adults, they’re normal. But if they’re large, symmetrical, or near the brainstem, they could point to vascular disease, MS, or even rare genetic disorders.
• Small lacunar infarcts: Tiny (3-5mm) strokes deep in the brain, often in the basal ganglia or thalamus. These usually come from high blood pressure. They might not cause symptoms, but they increase stroke risk over time.
• Enlarged ventricles: Bigger fluid spaces can mean brain shrinkage (atrophy). This happens with aging, Alzheimer’s, or long-term alcohol use. But if the ventricles are enlarged and the brain looks normal, it could be normal pressure hydrocephalus-a treatable condition.
• Masses or tumors: Brain tumors show up as abnormal growths. Gliomas (from brain cells) often have blurry edges. Meningiomas (from the lining) are round and push the brain aside. Contrast dye helps tell them apart.
• Microbleeds: Tiny dots of old blood. Seen on SWI. Common in elderly people with high blood pressure. More than 5 microbleeds raises concern for amyloid angiopathy, a condition linked to Alzheimer’s.
• Acute stroke: Bright on DWI, dark on ADC. This is urgent. If caught within 4.5 hours, clot-busting drugs can help. Delayed treatment means permanent damage.

One thing to remember: finding something on an MRI doesn’t mean it’s causing your symptoms. A 70-year-old with memory issues might have dozens of white matter lesions-but the real cause could be vitamin B12 deficiency or thyroid trouble. That’s why doctors never read MRI alone. They combine it with your history, exam, and blood tests.

When MRI Isn’t the Right Tool

Despite its power, MRI isn’t perfect. For sudden head trauma, CT is faster and better at spotting skull fractures and fresh bleeding. If someone’s unstable, in pain, or can’t lie still for 40 minutes, CT wins.

Also, MRI can’t always tell if a lesion is new or old. A bright spot could be from a stroke last week-or ten years ago. That’s why contrast dye (gadolinium) is sometimes used. New, active inflammation lets dye leak in, lighting up the area. Old scars don’t. But even contrast has limits-it can’t always distinguish between tumor recurrence and radiation damage.

And here’s the hard truth: brain MRIs are often ordered for headaches with no other symptoms. Studies show only 1.3% of these scans find something serious. The American College of Radiology says MRI is usually not appropriate for uncomplicated migraines. Yet they’re still done-because patients ask, and doctors want to be sure. That’s why understanding what’s normal-and what’s not-is so important.

What Happens After the Scan?

After your scan, a radiologist spends 20-30 minutes reviewing every image. They compare both sides of the brain, check for symmetry, and look at each sequence. Then they write a report. That report doesn’t come with pictures. It says things like: “Multiple small white matter hyperintensities consistent with small vessel ischemic disease.” That sounds scary. But what it really means? “Your small blood vessels have been affected by aging or high blood pressure.”

Your doctor will explain what it means for you. If the MRI shows a tumor, you’ll be referred to a neurosurgeon. If it’s MS, you’ll see a neurologist for treatment. If it’s just age-related changes? You might get advice on controlling blood pressure, quitting smoking, or exercising more.

There’s no magic number of lesions that means “disease.” It’s the pattern, location, and your symptoms together that matter.

What’s New in Brain MRI?

Technology keeps improving. High-field 7.0T MRI machines are now in a few academic centers. They can show brain layers so clearly, scientists are mapping how signals travel between neurons. AI tools can now cut scan time in half-helping patients who can’t stay still, like those with Parkinson’s or dementia.

Quantitative MRI is coming fast. Instead of just saying “there’s a lesion,” future scans will measure how much water is in tissue, how fast blood flows, or how much myelin is left. These numbers could track disease progression better than ever-helping doctors know if a new drug is working before symptoms change.

But the biggest change isn’t the machine. It’s the understanding that not every bright spot needs treatment. The goal isn’t to find every tiny change. It’s to find the ones that matter-for your health, your life, and your future.

What to Do Next

If your MRI shows something abnormal, don’t panic. Most findings are treatable-or even harmless. Ask your doctor: “What does this mean for me?” “Is this causing my symptoms?” “What’s the next step?”

If you’re healthy and your MRI came back normal, that’s good news. But don’t ignore lifestyle factors. High blood pressure, smoking, poor sleep, and inactivity all damage small blood vessels in the brain over time. Even if you don’t have symptoms now, protecting your brain starts today-with exercise, a healthy diet, and regular checkups.

Brain MRI isn’t magic. It’s a tool. Used right, it saves lives. Used wrong, it causes unnecessary worry. The best outcome isn’t a perfect scan-it’s understanding what you’re seeing, and what it means for your health.