Capsula Interna (Internal Capsule)

Capsula interna is one of the subcortical structures located deep in the cerebral cortex . Basal ganglia, thalamus, and brain stem are other subcortical brain structures. The anterior part of the capsule interna separates the caudate and lenticular nuclei, and the posterior part separates the thalamus and lenticular nuclei.

Capsule interna consists of nerve fibers (axons) that carry signals. This structure, which contains nerve fibers to and from the cerebral cortex, can be compared to a multi-lane highway with many intersections. It is part of the white matter. Its white color envelops the axons, giving it a myelin sheath that insulates and helps signals to be transmitted faster.

Nerve fibers in the interna capsule are necessary for movement and reception of sensations (hearing and vision). The pyramidal system, which connects the brain, spinal cord and muscles, and controls the skeletal muscles, passes through the interna capsule.

Anatomy

Capsula interna is similar in cross section to a boomerang. In the middle is the part it makes an angle (genu), in front of it are the parts defined as crus anterior (front leg) and behind it, the parts defined as crus posterior (hind leg). Frontopontine (from the frontal cortex to the pons) and thalamocortical (from the thalamus to the frontal cortex) nerve fibers pass from the front leg. Corticobulbar (cortex to brain stem) fibers pass from the genu part. Here are the fibers that control the facial and neck muscles. Corticospinal (from the cortex to the spinal cord) and sensory fibers pass from the hind leg. The auditory-related acoustic fibers to the temporal lobe and the visual-related visual fibers to the occipital lobe are in the hind leg.

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The interna fibers of the capsule open up and expand like a fan towards the cortex, forming the corona radiata. As the internal capsule continues down, the number of axons decreases because most axons terminate in the nuclei of the thalamus and brainstem.

The blood supply of the interna capsule is mainly from the lenticulostriate branches of the MCA . The forelimb may less frequently branch from the ACA . The hind leg is supplied with blood from the anterior choroidal artery branch of the ICA as well as the lenticulostriate branches .

Capsular Interna Stroke Findings

If the vessels feeding the internal capsule are blocked, a stroke develops. Heart disease, diabetes, high blood pressure are risk factors that pave the way for this. Even a small vascular occlusion in this area can lead to significant consequences. Symptoms differ according to the affected area.

Pure motor stroke: Weakness in one half of the face, one side of the arm and/or leg. It is one of the classical types of lacunar infarcts. Reflex increase called upper motor neuron signs, emergence of pathological reflexes (Babinski, Hoffman), clonus, spasticity can be seen.

Mixed sensorimotor stroke: The internal capsule contains both motor and sensory fibers. In a stroke involving the hind leg, loss of sensation may develop along with weakness on the opposite side of the body.

Muscle weakness and loss of sensation can also be seen in cortical stroke. For example, a patient presenting with arm and leg weakness may have a small internal capsule infarction or a large ACA+MCA cortical infarction. There are some clinical features that distinguish internal capsule stroke from cortical stroke. Diverting gaze, aphasia, visual field deterioration, visual or spatial neglect are the symptoms seen in cortical strokes. Imaging methods such as CT and MRI allow the location of the stroke to be determined.

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Treatment

Capsular interna stroke is not usually fatal and some recovery is expected. In the acute period, it is a priority to start preventive treatments in order to control vital signs, prevent complications and prevent recurrence of stroke. With physical therapy , applications are made to improve muscle strength, sensory and functional losses.

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