Internal capsule

Figure 1. Frontal section through human brain stained for acetylcholinesterase (frame A) and diagram showing locations of individual cholinergic cells irregularly dispersed throughout the nucleus basalis of Meynert and surrounding regions of human brain (frame B). Abbreviations AC, anterior commissure B, nucleus basalis of Meynert gpe, globus pallidus external part gpi, globus pallidus internal part, 1C internal capsule P, putamen.

The volume of tissue activated (VTA) by DBS is still the object of debate. Reference [12] developed a model to predict the effect of electrode location and stimulation parameters adjustments on tbe VTA and correlated the results of the model with clinical results recorded in a patient They showed that therapeutic DBS of the STN is characterized by a VTA that spreads well outside the borders of the STN (toward the internal capsule and thalamus). By increasing the voltage and keeping other parameters constant they observed that while rigidity continued to decrease, bradykinesia improved and then worsened (inverted U-shape) and side effects such as paresthesia appeared suggesting that both sensorimotor signs and side effects react differently to stimulation voltage. 

Previously, it has been thought that LA is limited to the supratentorial part of the brain, and even in that case they do not affect the internal capsule. However, with advancements in neuroimaging and research work, it recently became evident that similar lesions can be seen in the pons (Fig. 9.4) and the internal capsule (Fig. 9.5). The LA lesions around the horns of ventricles are usually homogeneous, while those in other regions of WM tend to appear as mul-... 

Fig. 13.3. FLAIR (left column) and diffusion-weighted transverse images (right column) in three patients with typical acute new ischemic subcortical lesions. Acute small subcortical lesions occurred in the pons (top row), internal capsule (center row), and lateral to the body of the right lateral ventricle...

Middle cerebral artery (MCA) territorial infarcts are the most common type of ischemic stroke. They can be divided in superficial (involving the cortex and the underlying white matter), deep (involving the basal ganglia, the internal capsule and the deep white matter) and combined (Bogousslavsky and Caplan 2001 Gorelick 1996). 

In primates and in many nonprimate mammals, the striatum is divided by the internal capsule into the caudate nucleus, located dorsomedially, and the putamen, located ventrolaterally. In other mammalian species, including the rat and the mouse, the bundles of the internal capsule traverse the striatum in the form of a brush rather than a plate (Nauta, 1989), and the striatum cannot, therefore, be subdivided in two entities, so that it is often referred to as caudoputamen or caudate-putamen (CPu). 

Fig. 2. A. Forebrain dopamine projection system in rodents and primates. The nigrostriatal pathway projects from the A8 and A9 groups of the substantia nigra (SN) via the medial forebrain bundle (mfb) to the neostriatum (NS). The mesocorticolimbic pathway projects from the more medially located A10 cell group of the ventral tegmental area (VTA) to the nucleus accumbens (NAcc) and olfactory tubercle (OT) of the ventral striatum (VS) and limbic forebrain areas including prefrontal cortex (Ctx), septum (Se) and amygdala (A). B. Striatal projection areas in the rodent brain are divided into the more dorsal neostriatum, and ventral striatum. C. In the primate brain, including human and illustrated for the marmoset, the neostriatum is divided by the fibers of the internal capsule into caudate nucleus (CN) and putamen (Pu). Correspondingly, the neostriatum of rats is sometimes designated the caudate-putamen (CPu) complex.

Fig. 1. Location of dopaminergic perikarya (Au-A15) are depicted schematically on frontal sections (B-F) through the diencephalon of the rat. Section A is a sagittal view of the rat brain depicting the rostrocaudal location of frontal sections B-F. Abbreviations AH, anterior hypothalamus ARC, arcuate nucleus BST, bed nucleus of the stria terminalis f, fornix ic, internal capsule inf, infundibulum me, median eminence mt, mamillothalamic tract OC, optic chiasm ot, optic tract PH, posterior hypothalamus PIT, pituitary gland PeV, periventricular nucleus PVN, paraventricular nucleus RCH, retrochiasmatic area SON, supraoptic nucleus VMN, ventromedial nucleus ZI, zona incerta.

A 39-year-old man developed bradykinesia and ataxia after smoking heroin. A brain MRI scan showed symmetrically increased signals in the white matter of the cerebellum, the peduncles, and the pons, with sparing of the dentate nuclei. There were abnormal signals in the posterior limb of the internal capsule and optic radiations. The signal abnormalities in this patient... 

In two reports from China 10 cases (nine men and one woman) of heroin-induced spongiform leukoencephalopathy have been reviewed. The first report discussed six cases with cerebellar signs and symptoms, with symmetrical lesions on neuroimaging in the white matter of the cerebellum, basal ganglia, posterior crus of the internal capsule, and the semi-oval center (25). The second report, described four cases that occurred during the abstinence period and showed improvement after 4 weeks of comprehensive treatment (26). 

Three cases of toxic and progressive spongiform leukoencephalopathy have also been reported as a result of vapor inhalation of heroin (21). There were generalized white matter abnormalities and pathology in the cerebellum, internal capsule, corpus callosum, and brain stem. 

The anterior choroidal artery arises from the last section of the internal carotid artery, just beyond the posterior communicating artery origin, and supplies the optic tract, internal capsule, medial parts of the basal ganglia, the medial part of the temporal lobe, thalamus, lateral geniculate body, proximal optic radiation and midbrain. Occasionally it arises from the proximal middle cerebral artery or posterior communicating artery. Minor twiglets... 

The anterior cerebral artery passes horizontally and medially to enter the interhemi-spheric fissure it then anastomoses with its counterpart of the opposite side via the anterior communicating artery, curves up around the genu of the corpus callosum and supplies the anterior and medial parts of the cerebral hemisphere. Small branches also supply parts of the optic nerve and chiasm, hypothalamus, anterior basal ganglia and internal capsule. 

The middle cerebral artery enters the Sylvian fissure and divides into two to four branches, which supply the lateral parts of the cerebral hemisphere. From its main trunk, a medial and lateral group of tiny lenticulostriate arteries and arterioles pass upwards to penetrate the base of the brain and supply the basal ganglia and internal capsule (Marinkovic et al. 1985). Some of these small penetrating vessels extend up into the white matter of the corona radiata in the centrum semiovale towards the small medullary perforating branches of the cortical arteries coming down from above. 

Acute or chronic cerebral injury may cause effects in remote areas of brain (Meyer et at 1993), so-called diaschisis, by reducing neuronal inputs and metabolic activity in the contralateral cerebellum and ipsilateral internal capsule, thalamus and basal ganglia after cortical lesions in the ipsilateral cortex following internal capsule and thalamic lesions and in the contralateral hemisphere. The functional consequences of diaschisis are not clear (Bowler et at 1995). 

Lacunar syndromes are defined clinically. They are highly predictive of small, deep lesions affecting the motor and/or sensory pathways in the corona radiata, internal capsule, thalamus, cerebral peduncle or pons. Although a few patients have a partial anterior circulation infarct (Bamford et al. 1987 Anzalone and Landi 1989 Arboix et al. 2007), the great majority have small iirfarcts, which are sometimes visible on CT, more often on MRI. These are caused by presumed occlusion of a small perforating artery affected by intracranial small vessel disease (see Fig. 10.2). There is no visual field defect, no new cortical... 

Pure motor stroke constitutes about 50% of lacunar cases. It consists of a unilateral motor deficit involving two or three areas, the face, upper arm and/or leg, including the whole of each area that is affected. There are often sensory symptoms but no sensory signs. The lesion occurs at locations where the motor pathways are closely packed together and separate from other pathways usually in the internal capsule or pons, sometimes the corona radiata or cerebral peduncle, and rarely in the medullary pyramid. There may be a flurry of immediately preceding TIAs, the so-called capsular warning syndrome (Donnan et al. 1996). 

Sensorimotor stroke constitutes about 35% of cases. It is the combination of a pure motor stroke with sensory signs in the affected body parts. The lesion is usually in the thalamus or internal capsule, but it can be in the corona radiata or pons. A similar clinical picture can be caused by cortical infarcts, leading to misclassification (Blecic et al. 1993). 

Ataxic hemiparesis constitutes about 10% of cases. It is the combination of corticospinal and ipsilateral cerebellar-like dysfunction affecting the arm and/or leg. It includes a syndrome in which there is little more than dysarthria and one clumsy hand. The lesion is usually in the pons, internal capsule or cerebral peduncle. Dysarthria, with or without upper motor neuron facial weakness, may also be a lacunar syndrome with similar lesion localization as ataxic hemiparesis, but there are other localizing possibilities as well. 

Fig. 10.2. These CT brain scans show a small hemorrhage in the left basal ganglia/ internal capsule (arrow) visible as a hyperintense area on day 1 that has become hypodense by day 3,...

Fig. 23.2. Axial T2-weighted image showing location of a spectroscopy voxel over the posterior limb of the internal capsule of each hemisphere together with the spectra obtained from the right and left internal capsules of a patient with subcortical stroke (Pendlebury et at. 1999). The N-acetyl aspartate (NAA) peak is reduced on the side of the affected right hemisphere consistent with damage to the descending motor pathways.

Pendlebury ST, Blamire AM, Lee MA et al. (1999). Axonal injury in the internal capsule correlates with motor impairment after stroke. Stroke 30 956-962 Pineiro R, Pendlebury ST, Smith S et al (2000). Relating MRI changes to motor deficit after... 

FIGURE 9.18 Coronal section of monkey brain stained for biotinylated albumin immediately after infusion of 5 [xL at 0.1 jxL/min. Gpi, Globus pallidus interna Gpe, Globus pallidus externa OT, optic tract Put, putamen IC, internal capsule. (Reproduced from Lonser RR et al. J Neurosurg 1999 91 294-302.)... 

The cerebral hemisphere and diencephalon have a more complex organization than that of the brainstem and spinal cord (Martin, 1989). The thalamus relays information from subcortical structures to the cerebral cortex via two different functional classes of nuclei namely, those that are for relay and those that are for diffuse projection. Three of the four anatomical divisions of the thalamus serve relay functions (anterior, medial, and lateral nuclei) and one is a diffuse projection nuclei (intralaminar). Thalamic neurons send the axons to the cerebral cortex via the internal capsule, as do cortical neurons that project to subcortical sites. There are two major somatosensory pathways the dorsal column of the medial lemniscal system, which mediates tactile, and vibration, and the anterolateral system, which mediates pain and temperature sense. 

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