Internal Capsular Stroke

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Top Contributors - Lucinda hampton and Dinu Dixon  

Introduction

The internal capsule, 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.

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.

Anatomy

Location

• The internal capsule is one of the subcortical structures of the brain.
• Subcortical structures: 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)
• Posterior limb: corticospinal fibers (cortex to spine), sensory fibers

Blood Supply

• Anterior limb: mainly fed by the lenticulostriate branches of middle cerebral artery(MCA), less often branches of anterior cerebral artery (ACA)
  • 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

Sub Heading 3

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 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.

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