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Topic

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Pyramid of vermis (VIII)

The pyramid of the vermis (lobule VIII) is a midline cerebellar lobule located in the posterior part of the inferior vermis, between the uvula (lobule IX) caudally and the tuber (lobule VII) rostrally. It forms part of the cerebellar vermis, which connects the two cerebellar hemispheres. The pyramid is relatively small and wedge-shaped, projecting posteriorly toward the cerebellar surface.

It plays a role in motor coordination, balance, and integration of vestibular and proprioceptive input. Dysfunction of the pyramid and adjacent vermis lobules may lead to truncal ataxia, gait disturbances, and postural instability.

Synonyms

  • Lobule VIII of vermis

  • Cerebellar pyramid

  • Pyramid of cerebellar vermis

Function

  • Coordinates axial and proximal limb movements

  • Integrates vestibular and proprioceptive signals for balance

  • Contributes to postural control and motor timing

  • Works with surrounding vermis lobules in gait and truncal coordination

MRI Appearance

T1-weighted images:

  • The pyramid appears isointense to cerebellar cortex and gray matter

  • Distinct from surrounding hypointense CSF of the fourth ventricle and cisterna magna

  • Provides anatomical contrast with adjacent lobules

T2-weighted images:

  • Appears isointense to cerebellar gray matter

  • CSF in the fourth ventricle and subarachnoid space is bright (hyperintense), outlining the pyramid

  • Useful for identifying atrophy, edema, or demyelination

STIR (Short Tau Inversion Recovery):

  • Gray matter of the pyramid remains intermediate signal

  • Abnormal pathology (edema, gliosis, tumor infiltration) appears hyperintense relative to normal tissue

  • Fat suppression increases conspicuity of adjacent lesions or edema

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal pyramid does not enhance

  • Pathological lesions (tumors, inflammatory foci, vascular malformations) show variable enhancement

  • Helpful in identifying neoplastic or inflammatory processes in the vermis

CT Appearance:

  • The pyramid of the vermis appears as a soft tissue density structure within the posterior fossa

  • Surrounded by hypodense CSF of the fourth ventricle and cisterna magna, providing natural contrast

  • CT is less sensitive for parenchymal detail but useful for calcification, hemorrhage, or mass effect on the posterior fossa

  • Atrophy appears as widened CSF spaces around the vermis

MRI images

Pyramid of vermis (VIII) of Cerebellum mri sag image -img-00000-00000