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White Matter Dissection of the Diencephalo-Mesencephalic Junction

Surgical Correlation


White matter dissection of the diencephalo-mesencephalic junction. As part of the Papez circuit, the column of the fornix (CF) ends at the mammillary body, which then connects to the anterior nucleus of the thalamus via the mammillothalamic tract (MTT) of Vicq-D'Azyr. The CF divides the hypothalamus into lateral and medial zones. The pineal gland is connected to the posterior wall of the third ventricle by the habenular commissure (HC) superiorly, and the posterior commissure (PC) inferiorly. The HC and PC together form the pineal stalk. The fasciculus retroflexus of Meynert (habenulo-interpeduncular tract) interconnects the habenula and the interpeduncular nucleus of the midbrain. The oculomotor nuclear complex is located anterior to the cerebral aqueduct.  From here, the intramesencephalic segment of the III nerve sweeps through the red nucleus and exits the midbrain in the interpeduncular fossa. The superior cerebellar peduncles (SCP; or brachium conjunctivum) decussate below the red nucleus in the caudal midbrain. Fibers from the SCP then ascend to form the capsule of the red nucleus. The medial longitudinal fasciculi (MLF), located one on either side of midline, contain mainly ascending (and some descending) fibers that interconnect the nuclei of cranial nerves III, IV, VI, and VIII (vestibular) and extend as far rostrally as the interstitial nucleus of Cajal in the lateral wall of the third ventricle. The MLF mostly coordinate eye movements in relation to head and neck positioning (vestibulo-ocular reflexes, or VORs).  The central tegmental tract (CTT) contains: 1) ascending fibers from the rostral solitary nucleus (gustatory) going to the ventral posteromedial nucleus of the thalamus, 2) ascending fibers from the reticular formation to the thalamus (part of the consciousness ascending reticular activating system) and 3) descending fibers from the red nucleus to the inferior olivary nucleus as part of the dentato-rubro-olivary pathway (Guillain-Mollaret). (Image courtesy of AL Rhoton, Jr.)