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Superior opening of the cerebral aqueduct

The superior opening of the cerebral aqueduct (also called the aqueductal inlet) is the anatomical structure where the cerebral aqueduct (aqueduct of Sylvius) begins at its upper end, marking the transition from the third ventricle into the narrow channel of the aqueduct. It plays a crucial role in cerebrospinal fluid (CSF) circulation between the third and fourth ventricles and is a key landmark in neuroimaging and neuroanatomy.

Synonyms

  • Aqueductal inlet

  • Rostral opening of cerebral aqueduct

  • Superior orifice of the aqueduct of Sylvius

  • Opening of the aqueduct (superior)

  • Apertura superior aqueductus cerebri (Latin)

Function

  • Allows cerebrospinal fluid (CSF) to flow from the third ventricle into the cerebral aqueduct

  • Facilitates CSF circulation towards the fourth ventricle and subsequently to the subarachnoid space

  • Acts as a critical checkpoint in the ventricular system, often assessed in cases of hydrocephalus or aqueductal stenosis

MRI Appearance

  • T2-Weighted Imaging:

    • Superior opening appears as a hyperintense (bright) round or slit-like area at the posterior-inferior aspect of the third ventricle

    • Surrounded by the hypointense periaqueductal gray matter

    • Aqueductal patency or obstruction can be assessed

  • T1-Weighted Imaging:

    • Appears hypointense (dark) due to CSF signal

    • Clearly visible as a small opening at the floor of the third ventricle

    • Adjacent brain structures show intermediate signal intensity

  • FLAIR Imaging:

    • The superior opening is generally hypointense (dark) because FLAIR suppresses free CSF signal

    • Useful for detecting periventricular lesions or edema that may affect aqueductal patency

    • Helps differentiate CSF from pathological hyperintensities

CT Appearance

  • Superior opening of the cerebral aqueduct is not directly visualized as a distinct structure on routine CT due to limited soft tissue contrast

  • Appears as a very small hypodense (dark) spot at the posterior floor of the third ventricle if the aqueduct is patent and if thin slices are used

  • Dilatation of the third ventricle or proximal aqueduct may be inferred in cases of obstructive hydrocephalus

  • Best evaluated in context of ventricular system anatomy rather than as a separate entity

MRI images

superior opening of the cerebral aqueduct mri 3t sagittal image