An MCA stroke is a stroke that occurs in the middle cerebral artery, the largest artery supplying blood to the brain. Because this single artery feeds such a wide territory, including parts of the frontal, temporal, and parietal lobes plus deeper structures, MCA strokes account for a large share of all ischemic strokes and tend to produce the classic symptoms most people associate with stroke: one-sided weakness, speech problems, and vision loss.
What the Middle Cerebral Artery Supplies
The middle cerebral artery branches off the internal carotid artery and delivers oxygenated blood to most of the lateral (outer) surface of the brain. Its territory covers regions responsible for movement, sensation, language, spatial awareness, and parts of vision. It also sends smaller branches, called lenticulostriate arteries, deep into the brain to supply the basal ganglia (involved in movement coordination) and the internal capsule (a major highway for nerve signals traveling between the brain and the body).
Because of this enormous territory, a blockage anywhere along the artery can knock out very different functions depending on exactly where the clot lodges. A blockage at the very start of the artery affects a much larger area than one in a smaller downstream branch.
What Causes an MCA Stroke
Most MCA strokes are ischemic, meaning a clot blocks blood flow. The two most common causes are cardioembolism and atherosclerosis. In a cardioembolic stroke, a blood clot forms in the heart, often because of an irregular heart rhythm like atrial fibrillation, and travels up into the brain where it lodges in the MCA. In an atherosclerotic stroke, fatty plaque builds up inside the artery wall itself, gradually narrowing it until blood flow is cut off or a piece of plaque breaks loose.
Less common causes include blood clotting disorders, arterial dissection (a tear in the artery wall), and vasculitis (inflammation of blood vessels). Risk factors overlap with those for stroke in general: high blood pressure, diabetes, smoking, high cholesterol, and heart disease.
Symptoms of a Left MCA Stroke
For most people, the left hemisphere is the dominant hemisphere for language. A left MCA stroke typically causes weakness or paralysis on the right side of the body, particularly the face and arm. Vision may be lost on the right side of both eyes.
Language problems are the hallmark of left-sided MCA strokes. If the blockage affects the upper branches of the artery (closer to the frontal lobe), the result is often difficulty producing speech. You may know what you want to say but struggle to get the words out. Speech becomes halting and effortful, though comprehension stays relatively intact. If the lower branches are affected (closer to the temporal lobe), the opposite pattern emerges: speech flows freely but doesn’t make sense, and the ability to understand others is severely impaired.
Symptoms of a Right MCA Stroke
A right MCA stroke causes weakness or paralysis on the left side of the body and may cut off vision on the left side of both eyes. Instead of language deficits, the signature problem is something called hemispatial neglect. A person with neglect isn’t just unaware of weakness on their left side; they may not recognize that the left side of their world exists at all. They might eat food only from the right half of a plate, shave only the right side of their face, or fail to notice people standing to their left.
This lack of awareness can make right MCA strokes deceptive. Because the person can still speak clearly, the stroke may initially seem less severe than it is, even though the functional impact on daily life can be enormous.
Deep Territory Strokes
Not all MCA strokes hit the brain’s surface. The small lenticulostriate arteries that branch off the main trunk supply deep brain structures. When these are blocked, the result is often pure motor weakness on one side of the body without the language or neglect problems seen in larger cortical strokes. Some deep strokes can also cause involuntary flinging movements of a limb or problems with coordination.
How Severity Is Measured
In the emergency room, clinicians use the NIH Stroke Scale (NIHSS) to rate stroke severity by testing strength, sensation, coordination, speech, language, visual fields, orientation, and facial symmetry. Scores range from 0 to 42:
- 0 to 5: Minor stroke
- 6 to 15: Moderate stroke
- 16 to 20: Moderate to severe stroke
- 21 to 42: Severe stroke
Large MCA strokes tend to score high on this scale because the artery’s territory covers so many of the functions being tested. These are often the most recognizable strokes, presenting with one-sided paralysis, forced eye deviation toward one side, visual field loss, and speech deficits all at once.
How It’s Diagnosed
A non-contrast CT scan of the head is usually the first imaging test because it’s fast and widely available. One of the earliest visible clues is the hyperdense MCA sign: a bright white spot on the scan where the clot is sitting inside the artery. This sign can appear within 90 minutes of stroke onset, often before any visible damage to brain tissue shows up. It has high specificity (about 95%), meaning when it’s present, a clot is almost certainly there. However, its sensitivity is moderate (around 52%), so a normal-looking scan doesn’t rule out an MCA stroke.
CT angiography, which uses contrast dye to visualize blood vessels directly, and MRI with diffusion-weighted imaging are commonly used next to confirm the location and size of the blockage and determine how much brain tissue is still salvageable.
Emergency Treatment
Time is the most important factor in MCA stroke treatment. The two main approaches are clot-dissolving medication given through an IV (thrombolysis) and mechanical clot retrieval through a catheter (thrombectomy).
IV thrombolysis is most effective within 4.5 hours of symptom onset. For people who wake up with stroke symptoms or have an unknown time of onset, updated 2026 AHA guidelines extend eligibility to 9 hours from the midpoint of sleep if imaging shows brain tissue that can still be saved. In select cases where thrombectomy isn’t available, thrombolysis may be considered up to 24 hours after onset when imaging confirms salvageable tissue.
Mechanical thrombectomy, where a catheter is threaded through an artery to physically pull out the clot, is the standard of care for large vessel occlusions in the MCA. It can be performed in an extended time window when imaging shows a mismatch between already-damaged tissue and tissue that’s at risk but not yet dead.
Malignant MCA Infarction
The most feared complication of a large MCA stroke is malignant MCA infarction, which occurs when massive swelling in the damaged brain tissue takes up so much space that it compresses healthy brain structures. This is defined as swelling that occupies more than 50% to 75% of the MCA territory. Without treatment, the fatality rate reaches up to 80%. A surgical procedure called decompressive craniectomy, where a portion of skull is temporarily removed to give the swelling brain room to expand, can be lifesaving in younger patients when performed early.
Recovery Timeline
Recovery from an MCA stroke follows a fairly predictable pattern, though outcomes vary widely depending on stroke size, location, and how quickly treatment was received. The fastest gains happen in the first 3 to 6 months, a period often called the critical window for recovery. During the subacute phase (roughly the first few months), people receiving rehabilitation can see upper extremity motor improvements of about 5% per week on standardized scales.
That rate slows but doesn’t stop. At around 12 months post-stroke, improvement rates drop to roughly 2.7% per week during active therapy, and by several years out, gains continue at about 1.4% per week. Research has shown that meaningful sensitivity to rehabilitation treatment extends well beyond one year, with a gradient that fades out over about 18 months before reaching a plateau. This challenges the older belief that recovery essentially stops at the 6-month mark.
What recovery looks like in practical terms depends heavily on which deficits the stroke caused. Arm and hand function tends to be the slowest to return, since the MCA’s territory heavily overlaps with the brain’s hand and arm motor areas. Language recovery after a left MCA stroke can continue for years with speech therapy. Neglect after a right MCA stroke often improves substantially in the first few months but can leave lasting subtle deficits in spatial awareness.