How to read a brain MRI, the images and the report

What you are looking at

A brain MRI is several series: stacks of slices taken with different settings, each of which makes different tissues bright or dark. The radiologist compares them side by side, because a finding is described by how it looks on each one.

The series description on the images usually names the plane — AX (axial, slices from top to bottom), SAG (sagittal, from the side), COR (coronal, from the front) — and the sequence. The ones you will meet in almost every brain MRI:

• T1 — the fluid around and inside the brain (cerebrospinal fluid) is dark. Good for anatomy: the grey matter of the surface and the white matter beneath are easy to tell apart.
• T2 — the cerebrospinal fluid is bright. Many abnormalities, which carry extra water, are bright too.
• FLAIR — a T2 image in which the fluid has been made dark again. It exists so that small bright spots right next to the ventricles and the surface of the brain are not drowned out by the fluid beside them. It is where most of the "spots" in a report are seen.
• DWI and ADC (diffusion) — they show how freely water moves. A recent stroke restricts that movement and lights up within minutes to hours, which is why diffusion is in every protocol.
• SWI or GRE — sensitive to blood products and calcium: old microbleeds show as small black dots.
• T1 with contrast (T1 + C, POST, GAD) — taken after an injection of gadolinium. Areas where the barrier between blood and brain is disrupted take up the contrast and turn bright.

One thing confuses almost everyone: on axial and coronal images the patient's right is on the left of the screen, as if you were facing them. Look for the R or L marker before deciding which side something is on.

Finding your way around

On an axial series, scrolling from the bottom up you pass the base of the skull and the cerebellum, then the brainstem, then the ventricles — the dark (on T1) or bright (on T2) fluid spaces in the middle, shaped like a butterfly — and finally the top of the brain, where the folds (gyri) and grooves (sulci) of the surface are clearest.

The brain should look roughly symmetrical, with the midline straight down the middle. A good part of what the report checks is exactly that: that nothing is pushing, that the ventricles are the expected size, and that the fluid spaces match the person's age.

Recognising structures helps you follow what your doctor tells you. It does not make you able to read the scan: normal variants, artefacts from movement and real findings can look alike, and telling them apart takes years of training and the full set of sequences.

The phrases in the report

These are the sentences that appear most often, normal and abnormal:

• No acute intracranial abnormality — nothing that needs urgent attention: no bleeding, no recent stroke, nothing compressing the brain.
• No restricted diffusion — no sign of a recent stroke on the sequence most sensitive to one.
• No mass effect or midline shift — nothing is pushing the brain out of place.
• Ventricles normal in size and configuration — the fluid spaces are what they should be.
• Normal flow voids — the large arteries look open; fast-flowing blood appears black on some sequences.
• Age-appropriate volume loss or age-related atrophy — the brain shrinks a little with age, and the spaces around it grow. "Appropriate for age" means it is what is expected.
• White matter hyperintensities, nonspecific T2/FLAIR hyperintense foci — small bright spots in the white matter. They become more common with age and are associated with high blood pressure and other vascular risk factors; they are also seen more often in people with migraine. "Nonspecific" means the image alone does not say what caused them.
• Chronic small vessel ischaemic change or microangiopathy — the radiologist's interpretation of those spots when their pattern fits wear of the small blood vessels. Some reports grade them on the Fazekas scale, from 0 (none) to 3 (large areas that run together).
• Incidental findings that are common and usually harmless: a pineal cyst, an arachnoid cyst, a developmental venous anomaly (a variant in how a vein drains), enlarged perivascular spaces, or mucosal thickening in the sinuses, which is often just the trace of a cold. Whether any of them needs follow-up is for the radiologist and your doctor to say, and the impression at the end of the report usually does.

The number worth knowing

Brain MRIs find things in people who feel perfectly well.

A study published in the New England Journal of Medicine in 2007 scanned 2,000 people aged 45 and over from the general population of Rotterdam — people taking part in a research study, not patients sent for a symptom. 7.2% had a silent stroke — an old infarct that had never caused symptoms —, 1.8% an aneurysm and 1.6% a benign tumour, most often a meningioma.

That is why "incidental finding" is such a frequent phrase in brain reports, and why it does not mean that something is wrong. We wrote about what incidental means here.

Questions worth taking to your appointment

• Does anything in the report explain the symptom that led to the scan?
• Are the white matter changes what you would expect at my age?
• Is anything described as new compared with a previous scan?
• Does any finding need a follow-up scan, and when?

If the report is hard to navigate, start with how a radiology report is structured: the impression at the end says which findings the radiologist considers important.

Sources

• Vernooij M.W. et al. Incidental findings on brain MRI in the general population. New England Journal of Medicine, 2007. The figures for the 2,000 people from Rotterdam come from here.
• Fazekas F. et al. MR signal abnormalities at 1.5 T in Alzheimer's dementia and normal aging. American Journal of Roentgenology, 1987. The original description of the scale used to grade white matter changes.

This explains vocabulary, not your brain. What a finding means for you depends on your symptoms, your history and your examination, which is what the person treating you is for.

What ExplainMyScan does is the step before that: you upload your report, say what worries you, and get it explained in plain language, so you walk into the appointment understanding what you are holding. It does not diagnose and it does not replace your doctor.