Lacunar infarct

What it means

Deep inside the brain, far from the larger arteries on its surface, tiny blood vessels called perforating arteries supply blood to small, specific regions. A lacunar infarct is a small stroke that happens when one of these tiny vessels becomes blocked, cutting off blood flow to the small area it feeds. The affected tissue dies and, over weeks to months, is gradually replaced by a small fluid-filled cavity, typically measuring under about 1.5 centimetres, which is what shows up on a later scan.

Why it appears on a CT or MRI report

Lacunar infarcts are seen on both CT and MRI, though MRI — particularly certain specialized sequences — is far more sensitive for detecting small or older ones. Reports describe the number, size, and location of these spots, which are typically found in deep structures such as the basal ganglia, thalamus, internal capsule, or brainstem, and pons. The radiologist will usually try to judge whether a lesion looks recent (acute) or old (chronic), and will often comment on it alongside related findings like white matter changes, since both are frequently caused by the same small-vessel disease process.

What it usually means

The leading cause of lacunar infarcts is small vessel disease, a gradual narrowing and stiffening of these tiny deep arteries driven mainly by long-standing high blood pressure, as well as diabetes, high cholesterol, smoking, and age. Because the affected areas are small, many lacunar infarcts, especially older ones found incidentally, never caused any symptoms the person noticed at the time — sometimes called a "silent" stroke. Others, depending on exactly which deep structure was affected, can cause distinct symptoms like sudden weakness or numbness on one side, slurred speech, or clumsiness, which typically prompted the scan that found them. Having one or more lacunar infarcts is an important marker: it signals that the same small-vessel disease process is also quietly at work throughout the brain's blood supply, which over time is linked to a higher chance of future stroke and, in some people, gradual cognitive changes.

When to follow up

A finding of a lacunar infarct, even an old and silent one, is worth discussing with your doctor, since it's a chance to tighten control of blood pressure, blood sugar, cholesterol, and smoking status — the modifiable factors that drive further small vessel damage. If the scan was prompted by new symptoms such as sudden weakness, numbness, slurred speech, vision change, or confusion, that is a medical emergency: treat it exactly as you would any stroke and seek emergency care immediately, since timing matters greatly for treatment. For incidental findings, your doctor may also screen for atrial fibrillation or other risk factors.

A plain-language way to picture it

Picture a garden watered by one wide main hose and dozens of thin capillary tubes branching off it to reach small individual flower beds. If one of those thin tubes gets pinched shut, the main lawn stays green, but that one small flower bed dries out and dies back, leaving a small bare patch. A lacunar infarct is that bare patch — small, deep, and easy to miss unless you're looking closely — but its presence is also a hint that the thin tubes throughout the garden may be more fragile than they used to be.