The cerebral aqueduct (aque ductus mesencephali, mesencephalic duct, sylvian aqueduct or aqueduct of Sylvius) is a narrow 15 mm conduit for cerebrospinal fluid (CSF) that connects the third ventricle to the fourth ventricle of the ventricular system of the brain. It is located in the midbrain dorsal to the pons and ventral to the cerebellum.^[1] The cerebral aqueduct is surrounded by an enclosing area of gray matter called the periaqueductal gray, or central gray. It was first named after Franciscus Sylvius.

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The cerebral aqueduct acts like a canal that passes through the midbrain. It connects the third ventricle with the fourth ventricle so that cerebrospinal fluid (CSF) moves between the cerebral ventricles and the canal connecting these ventricles.^[1]

Aqueductal stenosis, a narrowing of the cerebral aqueduct, obstructs the flow of CSF and has been associated with non-communicating hydrocephalus. Such narrowing can be congenital, arise via tumor compression (e.g. pinealoblastoma), or through cyclical gliosis secondary to an initial partial obstruction.^[1]

The cerebral aqueduct was first named after Franciscus Sylvius.^[3]

• Transverse section through mid-brain; number 2 indicates the cerebral aqueduct.
• Transverse section of mid-brain at level of inferior colliculi.
• Transverse section of mid-brain at level of superior colliculi.
• MRI section of mid-brain.
• Median sagittal section of brain.
• Scheme showing relations of the ventricles to the surface of the brain.
• Cerebral aqueduct
• Cerebral aqueduct
• Cerebral peduncle, optic chasm, cerebral aqueduct. Inferior view. Deep dissection.
• Cerebral peduncle, optic chasm, cerebral aqueduct. Inferior view. Deep dissection.
• Cerebrum. Inferior view. Deep dissection

• List of regions in the human brain