Posterior Commissure [Neurosurgery Wiki]

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====== Posterior Commissure ======

The '''posterior commissure''' is a small but important bundle of white matter fibers located in the dorsal part of the upper [[midbrain]], just above the [[cerebral aqueduct]] and posterior to the [[third ventricle]]. It serves primarily to connect the left and right [[pretectal nuclei]], enabling bilateral coordination of the [[pupillary light reflex]].

===== Anatomy =====

  * Located at the junction of the [[midbrain]] and [[diencephalon]]
  * Lies below the [[pineal gland]] and anterior to the [[superior colliculi]]
  * Runs transversely across the dorsal aspect of the upper brainstem
  * One of the key fiber tracts crossing the midline in this region, alongside the [[habenular commissure]]

===== Function =====

  * Mediates the **consensual pupillary light reflex**, allowing light in one eye to cause constriction in both pupils
  * Transmits signals from the [[pretectal nuclei]] to both [[Edinger-Westphal nuclei]]
  * Involved in reflexive eye movements and vertical gaze control

===== Clinical Significance =====

  * Lesions affecting the posterior commissure can result in:
    * [[Parinaud syndrome]] (dorsal midbrain syndrome)
    * Vertical gaze palsy
    * Loss of pupillary light reflex with preserved accommodation (light-near dissociation)
  * Commonly affected in pineal region tumors or tectal plate gliomas

===== Related Structures =====

  * [[Pretectal area]]
  * [[Edinger-Westphal nucleus]]
  * [[Pineal gland]]
  * [[Vertical gaze center]]

===== Reference =====

Nieuwenhuys R, Voogd J, van Huijzen C. ''The Human Central Nervous System''. Springer, 2007.