A lacunar infarct is a small stroke that occurs deep inside the brain, caused by a blockage in one of the tiny arteries that supply the brain’s inner structures. These infarcts measure between 3 and 20 millimeters in diameter and account for up to 25% of all strokes caused by blocked blood flow. Because they affect such a specific part of the brain’s blood supply, they produce a distinct set of symptoms and carry a different outlook than larger strokes.
How Lacunar Infarcts Happen
The brain’s deep structures are fed by very small arteries that branch off from larger ones. These tiny vessels have no backup supply, so when one gets blocked, the tissue it feeds loses oxygen and dies, leaving a small cavity (the word “lacuna” means “little lake” in Latin). Two main processes cause these blockages.
The most common is a condition where the walls of these small arteries gradually thicken with a waxy, glass-like material. High blood pressure drives this process, causing the vessel walls to swell inward until the opening narrows enough to cut off blood flow entirely. The second major cause is when a fatty plaque in a larger parent artery grows over the opening where a small branch splits off, sealing it shut. This is similar to what happens in heart disease, just on a much smaller scale.
Where They Occur in the Brain
Lacunar infarcts happen exclusively in the brain’s deep layers, not the outer surface. The most commonly affected areas include the basal ganglia (which help coordinate movement), the thalamus (a relay station for sensory information), the internal capsule (a dense bundle of nerve fibers connecting the brain to the spinal cord), and the pons (part of the brainstem). Each of these regions handles specific functions, so the location of the infarct determines which symptoms appear.
Five Classic Symptom Patterns
Neurologists recognize five distinct syndromes that lacunar infarcts produce. These are unusually predictable compared to other types of stroke, because each one maps to a specific deep brain structure.
Pure motor weakness is the most common pattern, occurring in 33% to 50% of cases. One side of the body becomes weak or paralyzed, but sensation, vision, and speech comprehension remain intact. The blockage is typically in the internal capsule or the base of the brainstem, where the nerve fibers controlling movement are tightly packed together.
Pure sensory stroke results from damage to the thalamus. You experience numbness, tingling, or sometimes burning pain on one side of the body, including the face, arm, leg, and trunk, but strength remains normal.
Ataxic hemiparesis is the second most frequent pattern. It combines weakness with clumsiness and poor coordination on the same side. The leg is usually more affected than the arm. Symptoms often develop over hours or days rather than appearing all at once.
Dysarthria with a clumsy hand causes slurred speech along with weakness and poor coordination in one hand. The tongue may deviate to one side when you try to stick it out.
Mixed sensorimotor stroke produces both weakness and sensory loss on one side. It combines features of the pure motor and pure sensory patterns.
Major Risk Factors
High blood pressure is the dominant risk factor. In a large study of over 3,000 people with lacunar strokes, 80% of those without diabetes and 92% of those with diabetes had hypertension. This makes sense given the way these strokes develop: sustained high pressure physically damages the small artery walls, setting the stage for blockages.
Diabetes is the second major contributor. About 37% of participants in that same study had diabetes, roughly double the 10% to 20% prevalence seen across all stroke types. Diabetes accelerates the thickening and stiffening of small blood vessels throughout the body, and the brain’s tiny arteries are especially vulnerable. Other risk factors include smoking, high cholesterol, and age.
How Lacunar Infarcts Are Detected
MRI is the standard tool for identifying lacunar infarcts. On a scan, they appear as small areas of damage in the deep brain tissue, measuring between 3 and 20 millimeters. CT scans can sometimes pick them up, but MRI is far more sensitive, especially for smaller infarcts and those in the brainstem.
Some lacunar infarcts are discovered incidentally, meaning they show up on a brain scan done for an unrelated reason. These “silent” infarcts caused no obvious symptoms at the time they occurred, but they still represent real damage. Their presence signals underlying small vessel disease and a higher risk of future strokes and cognitive decline.
Treatment and Prevention
Blood pressure control is the cornerstone of both treatment and prevention. Current guidelines from the American Heart Association support targeting a systolic blood pressure below 130 mmHg, based on strong evidence that more aggressive blood pressure lowering reduces stroke risk. Most people need two or more blood pressure medications to reach that target. In clinical trials aiming for even tighter control (below 120 mmHg), the average patient required about three medications.
The role of blood thinners is less straightforward for lacunar infarcts than for other stroke types. For people who have had a symptomatic lacunar stroke, antiplatelet therapy is part of standard stroke prevention. But for silent lacunar infarcts found incidentally on imaging, the evidence is much less clear. Because small vessel disease also increases the risk of brain bleeding, adding a daily aspirin could potentially cause more harm than benefit in some patients. The decision depends on individual risk factors rather than a one-size-fits-all approach.
Managing diabetes, quitting smoking, and treating high cholesterol are all part of reducing the chance of future events.
Recovery Outlook
Compared to larger strokes, lacunar infarcts generally carry a better prognosis for recovery. One important finding is that improvement continues well beyond the first few weeks. In a population-based study, about 33% of lacunar stroke patients showed meaningful functional improvement between 3 and 6 months after the event, a significantly higher rate than the 23% seen in other stroke types. Recovery continued between 6 months and 1 year, with roughly 20% of lacunar stroke patients still gaining function during that window.
Overall, 35% of lacunar stroke patients improved meaningfully between 3 months and 1 year, compared to 25% for other strokes. Beyond the one-year mark, further improvement became rare in both groups, with only about 12% showing additional gains. This timeline matters because it means rehabilitation efforts can pay off for many months after the initial stroke, and early plateaus don’t necessarily predict the final outcome.
The Bigger Picture: Small Vessel Disease
A single lacunar infarct is often a sign of a broader problem. The same process that blocked one small artery is likely affecting others throughout the brain. Over time, accumulating damage to these tiny vessels can contribute to problems with thinking, memory, and processing speed. This is one pathway to what’s known as vascular cognitive impairment. Controlling blood pressure and other risk factors isn’t just about preventing the next stroke. It’s about protecting the brain’s small vessel network as a whole.