Topics

Topic

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Posterior commissure

The posterior commissure is a slender, rounded bundle of white matter fibers that crosses the midline just dorsal to the cerebral aqueduct at the upper end of the cerebral aqueduct in the midbrain. It plays a crucial role in bilateral communication between the pretectal nuclei and is involved in coordinating the pupillary light reflex. Although small in size, the posterior commissure is an important anatomical landmark on neuroimaging and in neurosurgical procedures, due to its location near the pineal gland and its involvement in various visual and oculomotor pathways.

Synonyms

  • Epithalamic commissure

  • Commissura posterior (Latin)

Function

  • Mediates interhemispheric communication, especially for visual and oculomotor pathways

  • Plays a significant role in the pupillary light reflex, connecting pretectal nuclei involved in consensual pupil response

  • May also contribute to the coordination of vertical eye movements

Arterial Supply

  • Primarily supplied by branches of the posterior cerebral artery (PCA), especially the thalamoperforating arteries

  • Additional supply from the posterior choroidal arteries (branches of the PCA)

Venous Drainage

  • Drains mainly into the internal cerebral veins

  • Some drainage may occur into the vein of Galen (great cerebral vein)

MRI Appearance

  • T1-weighted (T1): Appears as a small, thin, isointense linear structure above the cerebral aqueduct and inferior to the pineal gland

  • T2-weighted (T2): Presents as a hypointense or isointense linear structure relative to surrounding brain tissue

  • FLAIR: Generally not well visualized due to its small size and location; appears as a subtle hypointense band

  • Post-contrast T1: Typically does not enhance; remains as a non-enhancing structure

CT Appearance

  • Difficult to visualize directly due to small size and low contrast with adjacent structures

MRI images

Posterior commissure mri 3t axial image