The posterior commissure is a bundle of fibres crossing the midline just above the opening of the cerebral aqueduct, below the stalk of the pineal gland, at the junction of the midbrain and diencephalon. Its fibres come from the pretectal nuclei and other upper midbrain nuclei. It is important for the pupil light reflex and vertical eye movements.
| Location | Posterior wall of the third ventricle, above the opening of the cerebral aqueduct and below the pineal gland |
|---|---|
| Connections |
|
| Blood Supply | Posterior cerebral artery (medial posterior choroidal and thalamoperforating branches) |
Links the pretectal areas of both sides so that both pupils constrict when light enters one eye, and helps coordinate vertical eye movements.
Damage at the posterior commissure, often from a pineal region tumour or midbrain stroke, causes Parinaud (dorsal midbrain) syndrome: loss of upward gaze, light-near dissociation of the pupils and convergence-retraction nystagmus. It forms the posterior point of the AC-PC line used in stereotactic surgery.
Upgaze palsy, abnormal pupils and convergence-retraction nystagmus from damage to the dorsal midbrain and posterior commissure.
A tumour such as a germinoma or pineocytoma that compresses the posterior commissure and aqueduct.
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