What Is a Small Vessel Stroke?

Also called a subcortical stroke

A small vessel stroke occurs when a small artery that branches off from a large artery in the brain becomes blocked or leaks. Since small vessel strokes occur deep within the subcortical region of the brain, they are also called subcortical strokes. This is in contrast to large vessel or cortical strokes, which affect the outer layer of the brain, or the cerebral cortex. 

Even though a subcortical stroke is generally small in location, it can cause noticeable signs and symptoms, like weakness or numbness on one side of the body. That said, a small vessel stroke is unlikely to cause life-threatening consequences, such as seizures or brain swelling.

In this article, we will review how small vessel strokes occur, and some of their possible symptoms. You'll also learn about some of the different locations in the brain where these strokes can develop.

Doctor and patient looking at anatomical model
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How Do Small Vessel Strokes Happen?

There are two main types of small vessel strokes:

  • Small vessel ischemic stroke: When a small artery deep within the brain becomes narrowed or blocked.
  • Small vessel hemorrhagic stroke: When a small artery deep within the brain leaks or bursts open.

As a result of a small vessel stroke, either hemorrhagic or ischemic, brain cells begin to die right away because they cannot receive the oxygen and nutrients they need to survive. This response to the lack of blood flow is called an infarction.

Hypertension is a major risk factor for all small vessel strokes. The elevated blood pressure can damage the walls of the tiny arteries, causing them to narrow or break open.

Small vessel ischemic strokes can also occur as a result of atherosclerosis—a condition in which fatty deposits (plaque) clog the arteries. They can also develop from blood clots that travel to the brain from elsewhere in the body. A traveling blood clot is called an embolus.

What Arteries Are Affected?

Arteries are blood vessels that carry oxygen-rich blood to vital organs throughout the body, including the brain.

Small vessel strokes affect small branches of three large arteries—the middle cerebral artery, anterior cerebral artery, and posterior cerebral artery.

These small branches are called penetrating, end arteries because they have no branches and "end" within the brain tissue.

The anterior and posterior cerebral arteries are part of the Circle of Willis—a network of arteries located at the base of your brain.

The middle cerebral artery is not part of the Circle of Willis, but it runs close by, branching off from the internal carotid artery, which runs along the side of your neck

What Brain Structures are Affected?

Small vessel strokes occur in structures deep within the brain, such as the thalamus, basal ganglia, internal capsule, and brainstem.

Thalamus

The thalamus serves as a critical hub area for collecting and integrating sensory signals (e.g., for taste, vision, and hearing) before relaying them to the outermost portion of the brain called the cerebral cortex.

Specifically, the right side of the thalamus transmits sensation from the left side of the body, and the left side of the thalamus transmits sensation from the right side of the body.

A small vessel thalamic stroke can cause numbness, tingling, or even complete loss of sensation of the face, arm, and leg.

The thalamus also plays a key role in relaying motor (movement) signals, regulating emotion and the sleep-wake cycle, and managing various cognitive processes like attention and memory processing.

That said, larger vessel thalamic strokes, not small vessel ones, typically cause impairment in one or more of these higher-order functions.

Basal Ganglia

The basal ganglia is a group of subcortical nerve cells that is highly connected with several brain areas, including the thalamus, brainstem, and cerebral cortex. The basal ganglia contains multiple structures, one of which, the substantial nigra, is affected in Parkinson's disease.

The basal ganglia controls sophisticated functions that require coordination and muscle movements. A stroke affecting the basal ganglia can cause symptoms such as writhing, twisting movements, muscle twitching, and/or tremor.

Internal Capsule

The internal capsule is located deep within the brain and is a white matter structure. The white appearance is a result of myelin, a specialized type of fat that covers brain and nerve cells to protect and insulate them, allowing the electrical signals to travel quickly and efficiently.

The internal capsule is primarily involved in regulating movement. As a result, symptoms of a small vessel stroke in this area may include mild weakness, severe weakness, or complete paralysis of the opposite face, arm, and leg.

In addition, the internal capsule is involved in carrying nerve signals related to sensation. Numbness on the opposite side of the body, therefore, may occur with a small vessel stroke in this area.

While the internal capsule also transmits visual and language information, these functions are uncommonly affected by small vessel strokes.

Brainstem

The brainstem connects your brain to your spinal cord and has many roles, such as helping to control your breathing, heartbeat, and blood pressure. It also helps controls your eye movements and swallowing. Motor and sensory nerve pathways also course through the brainstem.

Symptoms of a small vessel stroke in the brainstem may include weakness or sensory loss on the side of the body opposite the stroke. Eye movement problems or problems swallowing (dysphagia) may also occur.

Summary

A small vessel stroke, also called a subcortical stroke, is caused by the blockage or leaking of a small, deeply located branch of a larger artery in the brain. Hypertension is a major cause of small vessel strokes.

Symptoms of these strokes tend to affect movement and/or sensation on one side of the body. More complex functions, like language, vision, and cognitive processes, are not usually affected.

A Word From Verywell

A small vessel stroke is often the first sign of stroke risk factors, like hypertension, diabetes, or high cholesterol. This means that, in addition to recovering from the stroke itself, you will also need to get a medical checkup to see why you experienced a stroke. Most of the time, these risk factors can be well managed to reduce your risk of having another stroke.

With rehabilitation and risk factor management, you can achieve maximal recovery and prevention of additional strokes.

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8 Sources
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