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Cerebral aqueduct

The cerebral aqueduct, also known as the Sylvian aqueduct or aqueduct of midbrain, is a narrow cerebrospinal fluid (CSF) conduit connecting the third ventricle in the diencephalon to the fourth ventricle in the hindbrain. It runs through the mesencephalon (midbrain), bordered anteriorly by the periaqueductal gray matter and laterally by the tectal and tegmental structures.

The aqueduct serves as a critical channel for CSF flow, maintaining ventricular system continuity and intracranial pressure homeostasis. Its patency is essential, as stenosis or obstruction can lead to non-communicating hydrocephalus, with dilation of the lateral and third ventricles. The aqueduct is narrowest at the level of the midbrain tegmentum, making it a frequent site for congenital or acquired obstruction.

Function

  • Serves as the primary CSF passage between the third and fourth ventricles

  • Maintains ventricular system continuity

  • Plays a role in intracranial pressure regulation

  • Obstruction can cause hydrocephalus

Synonyms

  • Sylvian aqueduct

  • Aqueduct of midbrain

  • Cerebral aqueduct of Sylvius

MRI Appearance

T1-weighted images:

  • The cerebral aqueduct appears as a thin, hypointense linear structure within the midbrain

  • Surrounded by intermediate signal intensity midbrain parenchyma

  • CSF within the aqueduct is dark on T1

  • Post-contrast imaging generally shows no enhancement unless pathology (tumor, vascular lesion) is present

T2-weighted images:

  • The aqueduct lumen is hyperintense due to CSF

  • Midbrain parenchyma surrounding the aqueduct is intermediate signal

  • Narrowing or obstruction is detectable as abrupt CSF signal loss or upstream ventricular dilation

STIR (Short Tau Inversion Recovery):

  • CSF remains hyperintense

  • Surrounding midbrain edema or gliosis, if present, appears bright

  • Useful for detecting post-inflammatory changes, tumor infiltration, or edema

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal aqueduct shows no enhancement

  • Enhancement may indicate neoplasm, inflammatory lesion, or vascular malformation within or adjacent to the aqueduct

CT Appearance:

  • The aqueduct itself is usually not directly visible due to its narrow size

  • CSF density appears hypodense relative to brain parenchyma

  • Ventricular enlargement upstream may indicate obstruction

  • Excellent for detecting hydrocephalus, calcifications, or hemorrhage affecting the aqueduct or surrounding midbrain

MRI images

Cerebral aqueduct (Sylvian aqueduct) mri sag image -img-00000-00000

MRI images

Cerebral aqueduct (Sylvian aqueduct) mri axial image