Topics

Topic

design image
External capsule

The external capsule is a thin, white matter tract in the brain, located between the putamen medially and the claustrum laterally. It serves as an important anatomical landmark and conduit for neuronal fibers connecting various cortical and subcortical structures. While not as prominent as other internal tracts like the internal capsule, the external capsule plays a significant role in neuroanatomy and is often evaluated in neuroimaging studies, especially for its involvement in certain pathologies or as a reference for lesion localization.

Function

  • Composed primarily of association fibers, including corticocortical connections.

  • Transmits information between the cerebral cortex and subcortical areas, especially between the insular cortex and other cortical regions.

  • Plays a role in the integration and modulation of cortical activity.

  • Not primarily involved in motor or sensory pathways, but may be affected in various neurological conditions.

MRI Appearance

  • T2-weighted Imaging:

    • Appears as a thin, linear hypointense (dark) band between the hyperintense (bright) putamen and claustrum.

    • Sometimes subtle due to its small size and proximity to surrounding structures.

  • T1-weighted Imaging:

    • Appears as a thin, slightly hyperintense (bright) line between the gray matter of the putamen and claustrum.

    • Less conspicuous than on T2 due to less contrast with adjacent tissues.

  • FLAIR Imaging:

    • Usually hypointense, similar to T2 appearance.

    • May become hyperintense (bright) in pathological conditions such as demyelination, infarct, or edema.

CT Appearance

  • The external capsule is generally not well visualized on CT scans due to limited contrast between adjacent gray and white matter structures.

  • May be inferred as a thin white matter band between the denser putamen and the less dense claustrum, but typically indistinct.

  • Pathological changes such as infarct or hemorrhage in the adjacent areas may help outline the location of the external capsule indirectly.

MRI images

external capsule mri 3t axial image

MRI images

external capsule mri 3t coronal image