The basal ganglia are a group of grey matter nuclei located deep within the brain that are interconnected with the cerebral cortex, thalami and brainstem.
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Terminology
Whilst very widely used in English, the term 'basal ganglia' is actually a misnomer, as a ganglion is a collection of nerve cell bodies outside of the central nervous system. The equivalent within the central nervous system is termed 'nucleus', as reflected in the official term for the basal ganglia in the Terminologia Anatomica, 'nuclei basales', the English translation of which is 'basal nuclei'.
This is also illustrated by the name of each individual basal nucleus, e.g. caudate nucleus, lentiform nucleus, subthalamic nuclei, etc.
Gross anatomy
In a strict anatomical sense, the basal ganglia contains three paired nuclei that together comprise the corpus striatum:
Functionally, two additional nuclei are also part of the basal ganglia:
The caudate nucleus is located at the superomedial part of the internal capsule, while the putamen and globus pallidus are located at the inferolateral part. The anterior part of the caudate nucleus indents medially into the floor of the lateral ventricle. The inferior part of the caudate nucleus limits the roof of the temporal horn of the lateral ventricle. Medial to the caudate nucleus is the thalamus. Superior to the caudate nucleus lies the corpus callosum. The tail of caudate nucleus extends under the internal capsule behind the thalamus forming a roof with the inferior horn of lateral ventricle 4.
Arterial supply
The precise vascular anatomy of the basal ganglia can vary among individuals, nevertheless, the majority of the basal ganglia receives arterial supply from perforating branches from the middle cerebral artery, branches from the anterior cerebral artery, and terminal internal carotid artery.
Radiographic features
Ultrasound
Basal ganglia is isoechoic in head ultrasound 6. Hyperechoic basal ganglia would indicate edema, ischemia, or hemorrhage 7.
CT
Basal ganglia appears isodense to the cortex 5.
MRI
The basal ganglia are normally isointense to the cortex. As the globus pallidus has more myelin and calcium deposition compared with the putamen, it usually appears slightly more T1 hyperintense 5. When calcification exceeds 30%, there is signal loss in all sequences 5.
Iron is deposited within the globus pallidus, greater than in the putamen or caudate nucleus 3. This contributes to hypointensity of globus pallidus when compared to the putamen and caudate nucleus on T2/FLAIR sequences 5. Aging with consequent iron deposition in the putamen results in a gradual decrease of T2/T2*/SWI signal intensity in the putamen. This is most pronounced in the eighth or ninth decade of life, but can often be seen earlier.
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