Symptoms of white matter lesions in the hemispheres

In a horizontal section of the brain - the so-called Flechsig section - one can see the white subcortical matter (centrum semiovale) with the corona radiata and the internal capsule. Numerous conductors pass through the white matter of the brain tissue, connecting the cerebral cortex with the lower parts of the central nervous system.

The internal capsule (capsula interna) is a layer of white matter between the lentiform nucleus, on one side, and the head of the caudate nucleus with the thalamus, on the other. The internal capsule has anterior and posterior legs and a genu. The anterior leg is made up of axons of cells, mainly of the frontal lobe, going to the nuclei of the pons and to the cerebellum (fronto-pontine-cerebellar tract). When they are switched off, there are disorders of coordination of movements and body posture, the patient cannot stand or walk (astasia-abasia) - frontal ataxia. The anterior two-thirds of the posterior leg of the internal capsule are formed by the pyramidal tract, and the corticonuclear tract passes in the genu. Destruction of these conductors leads to central paralysis of the opposite limbs of the lower facial muscles and half of the tongue (hemiplegia).

The posterior third of the posterior leg of the internal capsule consists of axons of thalamic cells that conduct impulses of all types of sensitivity to the cerebral cortex and subcortical formations. When these conductors are switched off, sensitivity is lost on the opposite half of the body (hemianesthesia). These syndromes can sometimes be accompanied by hemianopsia due to the destruction of the optic radiation adjacent to the posterior lower parts of the internal capsule.

In capsular hemiplegia (or hemiparesis) there are all the signs of damage to the central motor neuron: muscle spasticity, increased deep reflexes, disappearance of superficial reflexes (abdominal and others), the appearance of pathological foot and wrist reflexes, pathological synkinesis and protective reflexes. The Wernicke-Mann pose is very characteristic: the upper limb is bent at all joints and brought to the body; the lower limb is straightened and makes circumductive (circling) movements when walking. There are several explanations for the occurrence of this characteristic pose. The occurrence of spasticity of the flexor muscles in the upper limbs and extensors in the lower limbs is caused by an increase in the tone of the antigravity muscles, the contractions of which are aimed at overcoming the force of gravity. This automatic regulation is carried out by reflexes of the brainstem (especially the vestibular systems), and such reflex arcs are disinhibited when the internal capsule is damaged.

The described typical symptoms of capsular movement disorders are somewhat different in the acute period of the disease (especially in the first days of cerebral strokes). Muscle tone and deep reflexes are not increased, but, on the contrary, are reduced. This is used in diagnostics to detect hemiplegia in patients in a comatose or deeply soporous state. If the upper limbs of a patient lying on his back are bent at the elbow joints and simultaneously lowered, the forearm on the side of hemiplegia will be the first to lower (due to lower muscle tone). For the same reason, on the side of paralysis, the lower limb is more rotated outward.

Capsular hemianesthesia concerns all types of cutaneous and deep sensitivity; in this case, unlike localization in the cortex, the sensitivity disorder affects the entire half of the body, since the conductors in the internal capsule are located compactly.

Hemianopsia with damage to the most posterior sections of the internal capsule of the beginning of the optic radiation differs from tractus by the preservation of the hemiopic reaction of the pupils to light. In this case, the central visual fields may fall out, which is not observed with damage to the cortex of the occipital fields (the projection zone of the visual analyzer).

In case of lesions of the supracapsular zone, the semi-oval center may cause a similar picture of disorders, but often a less pronounced picture of the “three hemi” is observed, and motor disorders predominate (in case of lesions of the anterior sections) or sensory and visual lesions of the middle and posterior sections of the semi-oval center.