We describe the anatomy of the basal nuclei as assessed by means of MRI.
The telencephalic nuclei are an important site of elaboration of neural impulse involved in body movements. They are gray formations placed deeply in the white matter of both the hemispheres.The
basal nuclei are composed of: 1. amygdala, also known as archistriatum, which belongs to the limbic system; 2. the claustrum and 3. the striated body that is constituted by the globus pallidus
(paleostriatum), putamen nucleus, and caudate nucleus (which together form the neostriatum). The globus pallidus amd the putamen nucleus are together called lenticular nucleus (Fig. 1a-1b). These
gray formations are the core of the extra-pyramidal system, which is a very important structure that regulates the correct organization of motion; in other words, it is the substrate which initiates
movements, relatively to external sensorial trigers to stimulate movement.The amygdala is situated in the posterior-medial part of the temporal lobe and can communicate with inferior horn of the
lateral ventricle. Above the amygdala the inferior side of the claustrum is present, and an internal capsule separates the amygdala from the putamen (Fig. 4b).The caudal portion of the amygdala
continues with the tail of the caudate nucleus. The claustrum is a thin gray layer located deeply in the insula cortex separated from it by the extreme capsule; it is connected with the neo-cortex
The striated body is composed of gray formations intersected with nervous fascicles creating the capsular system. The caudate nucleus is positioned in the superior-medial part; the putamen and globus
pallidus occupy the inferior-lateral part. The caudate nucleus has a head, a body and a tail and resembles a big comma with a sagittal direction in the hemisphere (Fig. 2a-b-c-3a-4a-b). On the
anterior side it delimits the frontal horn floor of the lateral ventricle and with its inferior part it delimits the temporal horn roof; on the medial side, there is the thalamus and above, the
nucleus is covered by the corpus callosum knee (Fig. 6b). The tail extends behind the thalamus, under the internal capsule delimiting the inferior horn arch of the lateral ventricle. The lenticular
nucleus is located beneath and on the lateral side of the caudate nucleus, it has a sagittal direction and in the coronal section has a triangular shape (Fig. 2a-b-4a-b-c-6a-b). The lateral medullary
lamina (white matter) separates the lenticular nucleus into an external part, the putamen with more gray substance, and into an internal part, the globus pallidus with less gray matter, which is
divided into two parts by the medial medullary lamina (Fig. 4b). Caudate and putamen nuclei are younger than the others nuclei, they also have a high neuronal density and a rich vascularization. In
these nuclei, there are small multi-polar neurons that are receptive and associative cells and big neurons that are efferent projection cells. The hemisphere white matter placed below the cortex near
to the surface is very wide and is hence called the semi-oval center (Fig. 3b); from this center the white fibers go toward the basal nuclei and create the internal, external and extreme capsules.
The corona radiata originates from different cortical territories and with its white fibers converges into the internal capsule (Fig. 2c-6b). The several fibers systems of the internal capsule, such
as the thalamus-cortex systems or the cortex-tegmental fibers that arrive at the middle-brain through the external capsule, converge into compact fascicles so that even small lesions (i.e. a middle
cerebral artery hemorrhage or ischemia) can lead to serious clinic symptoms (1). An MRI investigation allows the definition of the anatomy of basal nuclei and their relationship to white matter
tracts. For this, we use, in particular, sequences that are able to discriminate white and gray matter. The inversion recovery is a sequence with a high contrast resolution between the white and gray
matter and it thus allows a good definition of the anatomy in this region. This sequence is actually able to differentiate tissue with different T1(2-3).
Differential Diagnosis List
Anatomy of the base nuclei.
Anatomy of the base nuclei.