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Topic

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Crus II of ansiform lobule of cerebellum

The Crus II of the ansiform lobule is a posterolateral segment of the cerebellar hemispheres, forming part of the posterior lobe of the cerebellum. It lies caudal to Crus I and is continuous with the tonsillar region of the cerebellum. Crus II contributes to the fine coordination of voluntary movements, motor planning, and integration of sensory input with motor output.

Anatomically, Crus II is bounded medially by the primary fissure and anteriorly by Crus I, and laterally it merges into the hemispheric cortex of the posterior lobe. It contains cerebellar cortex gray matter on the surface and underlying white matter (arbor vitae), with deep cerebellar nuclei connections, including input from pontine nuclei and output via the dentate nucleus.

Function

  • Participates in coordination and precision of voluntary limb movements

  • Involved in motor planning and timing

  • Integrates somatosensory information with motor control

  • Supports cognitive-motor processing and procedural learning

Synonyms

  • Crus II cerebellum

  • Posterior segment of ansiform lobule

  • Cerebellar Crus II

MRI Appearance

T1-weighted images:

  • Crus II appears as gray matter cortical ribbon (intermediate signal intensity) overlying low signal white matter (arbor vitae)

  • Sulci and folia are visible as linear low-signal bands, separated by white matter

  • Structural detail is best on high-resolution sagittal and coronal T1 sequences

T2-weighted images:

  • Gray matter of Crus II is intermediate-to-high signal, while underlying white matter is hypointense, highlighting folial architecture

  • Fissures appear hyperintense relative to white matter

  • T2 is sensitive to edema, infarcts, or demyelinating lesions

STIR (Short Tau Inversion Recovery):

  • Gray matter remains intermediate signal, while areas of edema, inflammation, or gliosis appear hyperintense, enhancing detection of cerebellar pathology

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal Crus II shows no intrinsic enhancement

  • Abnormal enhancement may indicate neoplasm, vascular malformations, or inflammatory lesions

CT Appearance:

  • Crus II is part of the posterior cerebellar hemispheres, visualized as soft tissue density within the posterior fossa

  • Gray matter is slightly hyperdense relative to white matter

  • Sulci may be outlined by CSF, appearing hypodense

  • CT is useful for hemorrhage, calcification, or mass effect in the posterior fossa

MRI images

Crus II of ansiform lobule mri sag image -img-00000-00000