Basal ganglia

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.

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. 

Anatomy

In a strict anatomical sense, it contains three paired nuclei that together comprise the corpus striatum:

• caudate nucleus

• lentiform nucleus

  • putamen

  • globus pallidus

Functionally, two additional nuclei are also part of the basal ganglia:

• subthalamic nuclei

• substantia nigra

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 laterally to 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.

TerminologyRadiographic features

Whilst very widely usedBasal ganglia is isoechoic in head ultrasound is a collection of nerve cell bodies outside of the central nervous system⁶. The equivalent within the central nervous system is termed 'nucleus', as reflected in the official term for theHyperechoic basal ganglia inwould indicate oedema, ischaemia, or haemorrhage ⁷.

CT

Basal ganglia appears hypodense to the Terminologia Anatomica, 'nuclei basales', the English translation of which is 'basal nuclei'cortex ⁵.

MRI

The basal ganglia are normally isodense/isointenseisointense to the cortex. Because the globus pallidus has more myelin content and calcium deposition compared with the putamen, it usually appears slightly more hypointense on T2WI, GRE, and SWI images.

Age-related calcium deposition in the globus pallidus initially results in increased T1 signal intensity and subsequently, whenhyperintense ⁵. When calcification exceeds 4030%, signal there is signal loss in all sequences⁵.

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. Ageing 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.

Related pathology

• basal ganglia calcification 

• Parkinson disease

• Huntington disease

• Hallervorden-Spatz syndrome

• central pontine myelinolysis

• gliomatosis cerebri

• cerebral microhaemorrhage

 See also

• basal ganglia signal abnormalities

  • increased T2 signal in the basal ganglia

  • decreased T2 signal in the basal ganglia

  • increased T1 signal in the basal ganglia

  • decreased T1 signal in the basal ganglia

  • restricted diffusion in the basal ganglia

• basal ganglia calcification