Topics

Topic

design image
Globus pallidus internal segment

The globus pallidus medial segment (GPi), also known as the internal segment, is a principal nucleus within the basal ganglia complex, lying medial to the external segment (GPe) and lateral to the posterior limb of the internal capsule. The GPi is the major output nucleus of the basal ganglia, conveying inhibitory signals to the thalamus and brainstem, thus exerting powerful influence over voluntary movement control. Pathological changes in the GPi are associated with a variety of movement disorders, most notably Parkinson’s disease and dystonia.

Anatomical Features

  • Medial component of the globus pallidus, separated from GPe by the medial medullary lamina.

  • Lies lateral to the posterior limb of the internal capsule and medial to the GPe.

  • Composed of GABAergic neurons, with high iron and myelin content.

Function

  • Principal output nucleus of the basal ganglia.

  • Receives inhibitory input from the striatum and excitatory input from the subthalamic nucleus.

  • Sends inhibitory GABAergic projections to the thalamus and brainstem motor nuclei.

  • Plays a key role in suppressing unwanted movement and facilitating intended motor activity.

Arterial Supply

  • Mainly supplied by the medial 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 deep medullary veins and lenticulostriate veins.

  • Blood eventually empties into 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 hypointense relative to adjacent brain tissue.

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

MRI image

Globus pallidus medial segment mri 3t coronal image

MRI image

MRI Globus pallidus internal (medial) segment axial anatomy image -img-00000-00000