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Horizontal fissure (cerebellum)

The horizontal fissure of the cerebellum is one of the most prominent and anatomically significant fissures in the cerebellum. It transversely divides the cerebellar hemisphere into superior (upper) and inferior (lower) portions and serves as an important landmark in both anatomical dissection and neuroimaging. This fissure begins anteriorly near the anterior cerebellar notch and sweeps laterally and posteriorly across the hemisphere, demarcating the dorsal and ventral surfaces. Understanding its anatomy and imaging features is essential in clinical practice, especially for radiologists and neurosurgeons.

Synonyms:

  • Fissura horizontalis cerebelli (Latin)

  • Horizontal cerebellar fissure

Anatomy:

  • The horizontal fissure is the largest and deepest fissure of the cerebellum.

  • It starts in front near the anterior cerebellar notch and courses posteriorly and laterally.

  • Separates the cerebellar hemisphere into a superior (dorsal) and inferior (ventral) surface.

  • Runs parallel to the posterior and inferior margins of the cerebellar hemispheres.

  • Serves as an anatomical boundary between the lobules above (such as the quadrangular and simple lobules) and those below (like the inferior semilunar and gracile lobules).

Arterial Supply:

  • Superior surface (above fissure):

    • Supplied mainly by the Superior Cerebellar Artery (SCA)

  • Inferior surface (below fissure):

    • Supplied by branches of the Posterior Inferior Cerebellar Artery (PICA) and partially by the Anterior Inferior Cerebellar Artery (AICA)

  • The fissure itself does not have a separate arterial supply but is bordered by these vascular territories.

Venous Drainage:

  • Drained mainly by the Superior and Inferior Cerebellar veins

  • Superior surface veins drain into the Great vein of Galen and straight sinus.

  • Inferior surface veins drain into the transverse and sigmoid sinuses.

  • Venous drainage follows the surfaces divided by the fissure.

Function:

  • The fissure itself is a structural landmark and does not directly serve a functional purpose.

  • However, it demarcates functionally distinct regions of the cerebellar cortex, which are involved in coordination, balance, and fine motor control.

MRI Appearance:

  • Appears as a prominent curvilinear hypointense (dark) line on T1 and T2-weighted images, outlining the division between superior and inferior cerebellar hemispheres.

  • Best appreciated on coronal and sagittal planes.

  • Serves as an anatomical landmark for localizing lesions or masses in the cerebellum.

CT Appearance:

  • Seen as a thin, curving hypodense (dark) line, separating the density of the cerebellar cortex into superior and inferior sections.

  • More subtle than on MRI but may be visible in high-resolution, thin-slice images.

  • Useful in identifying cerebellar atrophy or mass effect by shifting of the fissure.

MRI images

Horizontal fissure MRI 3T coronal image

MRI images

Horizontal fissure MRI 3T sagittal image

CT image

horizontal fissure of cerebellum CT sag anatomy image -img-00001-00001