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Topic

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Globus pallidus external segment

The globus pallidus external segment (GPe) is a key structure within the basal ganglia, lying lateral to the internal segment (GPi) and medial to the putamen. The GPe is part of the indirect pathway of the basal ganglia, which is critical for the inhibition and regulation of voluntary movements. Composed mainly of GABAergic neurons, the GPe is heavily involved in the modulation and relay of motor signals between other basal ganglia nuclei and the thalamus. Damage or dysfunction in this region is associated with movement disorders such as Parkinson’s and Huntington’s disease.

Anatomical Features

  • Lateral component of the globus pallidus, separated from GPi by the medial medullary lamina.

  • Located medial to the putamen and lateral to the internal capsule.

  • High in iron and myelin content, influencing imaging appearances.

Function

  • Central to the indirect pathway of the basal ganglia.

  • Receives inhibitory input from the striatum.

  • Sends inhibitory projections to the subthalamic nucleus.

  • Modulates the activity of the GPi and helps regulate voluntary motor control.

Arterial Supply

  • Primarily supplied by lateral lenticulostriate arteries (branches of the middle cerebral artery).

  • Additional minor supply from the anterior choroidal artery (branch of the internal carotid artery).

Venous Drainage

  • Drained by the deep medullary and lenticulostriate veins.

  • Blood eventually reaches the internal cerebral veins.

MRI Appearance

  • T1-weighted:

    • GPe appears relatively hyperintense (brighter) compared to the putamen and surrounding gray matter, due to iron and myelin content.

  • T2-weighted:

    • GPe is hypointense (darker) compared to the putamen and surrounding structures, owing to high iron deposition.

  • FLAIR:

    • GPe remains hypointense (dark), similar to its appearance on T2-weighted imaging, but contrast with white matter is somewhat reduced.

CT Appearance

  • On non-contrast CT, the GPe is isodense to slightly  hypointense relative to adjacent brain tissue.

  • Differentiation from GPi and putamen is limited on CT without pathology or calcification.

MRI images

Globus pallidus external segment mri 3t coronal image