Cerebral aqueduct

Aqueductus mesencephali (Sylvii)

NervousOrgansHead

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What it is
The narrow canal through the midbrain, between the tectum behind and the tegmentum in front, joining the third and fourth ventricles.
Function
The only route for CSF from the forebrain ventricles to the fourth ventricle.
Size
About 1.5 cm long and only 1-2 mm wide
Clinical note
Being the narrowest point of the ventricular system, it is the commonest site of congenital obstruction (aqueduct stenosis) causing hydrocephalus in infants.

Nearby nervous structures Fornix, Hypothalamus, Midbrain, Oculomotor nerve root (CN III), Optic tract, Optic tract root (CN II), Pons, Tentorium cerebelli, Trigeminal nerve root (CN V), Trochlear nerve root (CN IV)