Brain Anatomy Part III
Section X. Basal Ganglia, Thalamus, Hypothalamus
The major deep gray structures of the cerebral hemisphere are the putamen, globus pallidus, caudate, and thalamus. These can be grouped and categorized in different ways based on development, function, or location. For example, the caudate nucleus and putamen share similar function (receives input) and are together called the striatum. Similarly, the globus pallidus internus and pars reticulata of the substantia nigra are the main sources of basal ganglia output and histologically similar, but anatomically divided by the internal capsule. The putamen and the globus pallidus are closely juxtaposed, together called the lentiform nucleus. The caudate, putamen, and globus pallidus are usually considered to constitute the basal ganglia.
The basal ganglia are involved in numerous functions including motor control. To accomplish these functions, the basal ganglia is a key component via complex circuits communicating with cerebral cortex and other nuclei via white matter tracts. The basal ganglia are susceptible to a wide range of pathology, in particular unilateral or asymmetric lacunar infarcts. Bilateral involvement can be seen with neurodegenerative, toxic/metabolic, and global anoxia categories.
Another structure key structure is the thalamus, or 'relay station.' The thalamus is a very complex structure with numerous internal nuclei and diverse functions. Most of these nuclei are not well resolved on routine clinical imaging, but may become apparent when selectively involved by certain conditions. However, general regions differences are seen, for example the ventral nuclei are relatively heavily myelinated, usually without a sharp border with the posterior limb of the internal capsule on imaging.
Ventral Globus Pallidus
The dorsal and ventral globus pallidus, separated by radiations from the anterior commissure.
Huntington's Disease
Axial MRI in a patient with Huntington's disease demonstrates atrophy of the bilateral caudate nuclei, whic are barely perceptable. Thus, the frontal horns of the lateral ventricles appear disproportionately enlarged.
Normal DAT Scan
Note the normal 'comma' shape of activity, which could become truncated posteriorly in the setting of Parkinsonism. While a DAT scan does not effectively discriminate amongst the different types of Parkinsonism, it can differentiated Parkinsonism from other etiology of tremor such as essential tremor.
General Regions of Key Functional Categories
The thalamus is a structure with numerous internal nuclei and functions. Although a gross oversimplification, approximate general regions of key functions are depicted.
Key Vascular Territories
The thalamus has several major vascular territories, all supplied by the PCA and approximated here. Lacunar infarcts involving different zones can lead to widely differing clinical manifestations.
Acute Thalamic Lacunar Infarct
Patient with an acute lacunar infarct in the sensory region including the Ventrocaudal (Vc) nucleus of the thalamus, presenting with acute left hemi-sensory loss. The Vc nucleus reflects terminology used by most functional neurosurgeons, although commonly referred to as the VPL/VPM in medical school
Hockey-Stick Sign of the Thalami and Bilateral Basal Ganglia Involvement with Creutzfeldt-Jacob Disease
Patient with Creutzfeldt-Jacob disease. There is T2 hyperintensity and restricted diffusion in the basal ganglia bilaterally as well as the thalami in a hockey-stick configuration (MD and pulvinar nuclei regions). Although the hockey-stick pattern has been described in the variant version of the disease, it can occur in the non-variant form.
Coronal Image, Mid-Hypothalamus
Lining the third ventricle, the hypothalamus contains multiple nuclei. These can be characterized as medial and lateral regions and different sets of groups from anterior to posterior. The fornix pierces the hypothalamus, dividing it into medial and lateral areas.
Eagle-Wing Appearance
Axial image, level of hypothalamus. There is an eagle-wing appearance. The optic tracts are teh wings, the hypothalamus forms the legs, and the mamillary bodies (of the hypothalamus) form the talons.