Cerebral Aqueduct: The Canal Connecting Third and Fourth Ventricles

The cerebral aqueduct (also called the aqueduct of Sylvius, after 17th-century anatomist Franciscus Sylvius) is the narrow midline channel within the midbrain that connects the third ventricle (in the diencephalon) to the fourth ventricle (in the hindbrain).

Anatomical Details

Location: Dorsal midbrain (tectum), ventral to the corpora quadrigemina (superior/inferior colliculi).
Dimensions: ~15 mm long, 1–2 mm diameter—narrowest part of the ventricular system.
Lining: Ependymal cells (ciliated simple cuboidal epithelium).

Function

Allows cerebrospinal fluid (CSF) flow from lateral ventricles → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space (via foramina of Luschka and Magendie) → arachnoid granulations → venous sinuses.

Clinical Significance

Aqueductal stenosis (congenital or acquired from hemorrhage, tumor, infection) obstructs CSF flow → non-communicating hydrocephalus → upstream ventricular dilation (third/lateral ventricles), increased intracranial pressure. Treated with endoscopic third ventriculostomy (ETV) or shunt placement.

Pineal region tumors (germinomas, pineoblastomas) commonly compress the aqueduct due to anatomical proximity.