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The internal capsule (IC), a white matter structure, is a unique location where a large number of motor and sensory fibers travel to and from the cortex. Damage of any kind in this location will cause some relatively unique findings that can allow you to localize the lesions to the internal capule by exam alone.[1]
Image: Schematic illustration of projection fibers Internal Capsule
Structure
The internal capsule is a deep subcortical structure that contains a concentration of afferent and efferent white matter projection fibres. Anatomically, this is an important area because of the high concentration of both motor and sensory projection fibres. Afferent fibres pass from cell bodies of the thalamus to the cortex, and efferent fibres pass from cell bodies of the cortex to the cerebral peduncle of the midbrain. Fibres from the internal capsule contribute to the corona radiata.[2]
Anatomy
Location: The internal capsule is one of the subcortical structures of the brain. Subcortical structures include: internal capsule, caudate, putamen, globus pallidus, thalamus, brainstem
The anterior limb of the internal capsule separates the caudate nucleus and lenticular nucleus
The posterior limb separates the thalamus and lenticular nucleus
Types of fibers
Anterior limb: frontopontine fibers (frontal cortex to pons), thalamocortical fibers (thalamus to frontal lobe)
Genu (angle): corticobulbar fibers (cortex to brainstem)
The lenticulostriate arteries are small penetrating blood vessels that supply blood flow to most of the subcortical structures.
Genu: lenticulostriate branches of MCA
Posterior limb: lenticulostriate branches of MCA & anterior choroidal artery (AChA) of internal carotid artery[1]
Image 2: At the circle of Willis the internal carotid arteries branch into smaller arteries that supply blood to over 80% of the cerebrum.[3]
Causes
An internal capsule stroke is caused by interruption of blood supply in the middle cerebral artery (MCA) or one of its small branches. 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, called a lacune lacunar stroke.
It may also be caused by a thrombotic blood clot developing within one of the small arteries that supply blood to the internal capsule.
Symptoms
An internal capsule stroke can cause arm, hand, leg, or foot weakness, described as hemiparesis or hemiplegia.
An internal capsule stroke may also affect the the movement of the muscles in the face, making it difficult to chew, swallow or speak clearly.
The internal capsule is a pathway connecting nerves that control the sensation as well as the motor function, lesion in the capsule can cause severe weakness or sensory loss in the affected arm, leg or face.
IC CVA
The internal capsule is prone to cerebrovascular accidents because the perforating arteries that supply the region are predisposed to occlusion or rupture due to their small diameter.
Ischemic strokes secondary to blockage of the perforating arteries are known as lacunar strokes. The mechanisms of lacunar strokes include lipohyalinosis of perforating blood vessels, atherosclerosis of the large trunk vessels that supply perforators, and embolic occlusion of the perforating arteries. Lipohyalinosis of perforating arteries is the most common cause of lacunar strokes, and it correlates with states of chronic hypertension. It also has associations with diabetes and hyperlipidemia. The hallmark of lipohyalinosis is vessel wall thickening leading to a reduction of luminal diameter.
Lacunar strokes
Lacunar strokes primarily affect the deep structures of the brain, such as the putamen, caudate nucleus, thalamus, and internal capsule. Depending on the location of a lesion, the symptoms of lacunar strokes will require differentiation from cortical strokes. These deep strokes usually have an absence of cortical deficits such as seizures, aphasia, agnosia, and dysgraphia. Other cortical deficits include apraxia, alexia, and amnesia.
The progression of symptoms of lacunar strokes are abrupt in onset and evolve within minutes. In some cases, the symptoms may develop over several hours. Many variations on lacunar stroke syndromes exist.
Classic lacunar strokes syndome that arises from lesions of the internal capsule are pure motor strokes, ataxic hemiparesis, and clumsy hand-dysarthria.
Pure motor strokes have a characteristic presentation of contralateral hemiparesis that affects the face, arm, and leg in equal parts.
Ataxic hemiparesis presents with a combination of ataxia and weakness on the same side of the body. These stroke syndromes can include secondary to lesions of the posterior limb of the internal capsule.
Clumsy hand-dysarthria presents with difficulty with the articulation of speech and weakness in the hands and result from damage to the anterior limb of the internal capsule or genu.
Understanding the diverse blood supply of the internal capsule and the function of each limb are important for characterizing lesions of the internal capsule.[4]
Rehabilitation after internal capsule stroke requires an individualized approach and will depend on what kind of secondary effects you experience.
Although every stroke is unique, recovery from any type of stroke ultimately relies on neuroplasticity.
Neuroplasticity is the brain’s ability to rewire itself so that functions affected by stroke can be recovered through massed practice.
The more stimulation to the brain, the more rewiring occurs, and the more efficient functions become.
Common rehabilitation therapies for internal capsule stroke include:
Physical Therapy. Physical therapy help clients recover motor functions through exercise. Frequent and repetitive muscle activation is necessary to stimulate connections between the brain and muscles.
Speech Therapy. If internal capsule stroke caused facial weakness, speech therapy can help. A speech-language pathologist helps guide client through exercises specifically designed to strengthen the muscles around the mouth making chewing, swallowing, and speech more effective.
Occupational Therapy. Some of the effects of an internal capsule stroke could make it difficult to engage in typical daily tasks, such as dressing, bathing, and toileting. Occupational therapy helps client to regain some of their independence, and can also focus on strengthening upper extremity and improving coordination skills.
Sensory Reeducation. To restore sensation, stroke survivors should work on sensory reeducation exercises. They help stimulate the brain to promote the rewiring of sensory processing for properties like texture and temperature.
Visual Restoration Therapy. If client is experiencing visual field cuts after internal capsule stroke, visual restoration therapy may help. It involves using light to stimulate the boundary between visible and blind spots in the vision.
Whether client is trying to relearn how to control movements or recover sensation, it’s all about stimulating the brain through repetitions[6]
Links
For Physiotherapy specific assessment, treatment and more see here.
