The basal ganglia are a group of grey matter nuclei in the deep aspects of the brain that is interconnected with the cerebral cortex, thalami and brainstem.

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.

Anatomy

In a strict anatomical sense, it 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 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.

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 content 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 are particularly deposited within the globus pallidus, greater than putamen and caudate nucleus ³. This contributes to hypointensity of globus pallidus when compared to putamen and caudate nucleus on T2 an FLAIR weighted images 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 more pronounced in the 8^th or 9^th decade of life.