Internal Capsule Stroke Overview

Health worker assisting a disabled woman in walking
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An internal capsule stroke is a relatively small stroke that can cause profound weakness of one side of the body. The internal capsule is a region in the brain, and a stroke that affects the internal capsule causes characteristic symptoms.

What Is the Internal Capsule?

The internal capsule describes a region deep in the brain that functions as a communication pathway. The internal capsule allows communication between areas of the cerebral cortex, and areas of the brainstem.

These connections that are made possible by the pathways of the internal capsule are necessary for physical movement and perception of sensory information. 

The biggest job of the internal capsule is working as a relay station for the body’s motor function. This means that the internal capsule is necessary for arm, leg, trunk and face movement. The right side of the internal capsule transmits nerve signals for movement of the left side of the body and the left side of the internal capsule transmits nerve signals for movement of the right side of the body.

While the internal capsule is primarily involved in movement, it also acts as a relay station for sensation on the opposite side of the body.

The internal capsule is described as ‘white matter’ because of its appearance under a microscope. The internal capsule is also often referred to as the subcortical area of the brain because it is located below the cerebral cortex.

Symptoms and Diagnosis

An internal capsule stroke can cause arm weakness, hand weakness, leg weakness or foot weakness, described as hemiparesis or hemiplegia. You might have some strength left in the affected area (hemiparesis,) or you might not be able to move it at all (hemiplegia.) An internal capsule stroke may affect the face, making it difficult to chew, swallow or speak clearly.

The internal capsule is a pathway connecting nerves that control your sensation as well as your motor function, an internal capsule stroke can cause you to lose some or all sensation in the affected arm, leg or face.

Because so many important pathways run through the internal capsule, a relatively small internal capsule stroke can cause severe weakness or sensory loss.

If you have had an internal capsule stroke, it can usually be visualized on brain MRI or brain CT scan within a short time after the stroke. However, because internal capsule strokes are small, sometimes they are not clearly apparent in brain imaging studies, even when they cause profound symptoms.

Causes

An internal capsule stroke is caused by interruption of blood supply in the middle cerebral artery (MCA) or one of its small branches.

Usually, an ischemic internal capsule stroke is caused by an embolic blood clot coming from elsewhere in the body and blocking one of the small branches of the MCA. It may also be caused by a thrombotic blood clot developing within one of the small arteries that supplies oxygen-rich blood to the internal capsule. An embolic stroke or a thrombotic stroke usually occurs when cerebrovascular disease or heart disease develops after years of stroke risk factors.

A brain aneurysm or a hemorrhagic stroke may affect the internal capsule, although these are not common causes of an internal capsule stroke.

Outcome

The vast majority of internal capsule strokes are not fatal, and most people experience a degree of recovery. Most of the time, internal capsule strokes do not cause the severe swelling or seizures that are associated with strokes in other regions of the brain.

After an internal capsule stroke, you may continue to experience weakness of one side of your body, and you will likely experience some degree of improvement with physical therapy and stroke rehabilitation, although recovery is variable between one stroke survivor and another.

Usually, after a stroke of the internal capsule, you should expect to have a medical evaluation to see if you have any stroke risk factors. If this evaluation identifies stroke risk factors, such as heart disease, diabetes, hypertension or a blood disorder, you might need to make some changes in your lifestyle or start on new medications.

A Word From Verywell

An internal capsule stroke is often considered a small stroke. Internal capsule strokes rarely lead to life-threatening consequences. However, they are important warning signs of stroke risk factors. Controlling stroke risk factors with medication or lifestyle changes significantly reduces the risk of stroke.

Source:

Lesion location and cognitive impact of cerebral small vessel disease, Biesbroek JM, Weaver NA, Biessels GJ, Clin Sci (Lond). 2017 Apr 25

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