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Superior medullary velum

The Superior Medullary Velum is a thin, triangular lamina of white matter located in the posterior part of the brainstem. It forms the upper part of the roof of the fourth ventricle, extending between the two superior cerebellar peduncles. The superior medullary velum lies just beneath the cerebellum and above the fourth ventricle, contributing to the communication between the cerebellum and the midbrain. It is an important anatomical landmark and provides a surface for the attachment of the frenulum of the superior medullary velum and the trochlear nerves (cranial nerve IV), which are the only cranial nerves to emerge from the dorsal aspect of the brainstem.

Synonyms

  • Anterior medullary velum

  • Valve of Vieussens (historical)

  • Superior medullary lamina

Arterial Supply

  • Supplied primarily by the superior cerebellar artery (branch of the basilar artery)

  • Small contributions may come from the posterior cerebral artery branches

Venous Drainage

  • Drained by the superior cerebellar veins

  • Venous blood flows into the great cerebral vein of Galen and straight sinus

Function

  • Acts as a structural component forming the roof of the upper part of the fourth ventricle

  • Provides a pathway for the trochlear nerve (cranial nerve IV) as it decussates and emerges dorsally

  • Serves as an anatomical separation between the cerebellum above and the fourth ventricle below

MRI Appearance

  • Appears as a thin, hypointense (dark) line of white matter on T1-weighted images

  • On T2-weighted images, it is also hypointense relative to surrounding CSF but may be harder to distinguish due to its thinness and close relation to CSF

  • Best visualized in sagittal and axial planes as a thin structure connecting the superior cerebellar peduncles

CT Appearance

  • Usually not well visualized on CT due to its thinness and lack of contrast with surrounding CSF

  • May appear as a subtle, linear structure between the superior cerebellar peduncles if thin slices are used, but typically not a focus of routine CT imaging

MRI images

Superior medullary velum MRI 3T axial image

MRI images

Superior medullary velum MRI 3T coronal image

MRI images

Superior medullary velum mri 3T sagittal image

CT image

Superior medullary velum of cerebellum CT sag anatomy image -img-00001-00001