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Anterior horizontal ramus of Sylvian fissure

The anterior horizontal ramus of the Sylvian fissure is a key anatomical subdivision of the lateral sulcus (Sylvian fissure) of the brain, located on the lateral aspect of the cerebral hemisphere. This ramus extends anteriorly and horizontally from the main stem (sphenoidal segment) of the Sylvian fissure, marking the boundary between the inferior frontal gyrus and the insular cortex. It is of clinical and radiological significance due to its relationship with adjacent brain structures, vascular territories, and its distinct appearance on neuroimaging.

Synonyms

  • Horizontal ramus of the lateral sulcus

  • Horizontal branch of the Sylvian fissure

  • Anterior horizontal branch of the lateral fissure

Function

  • Serves as an anatomical landmark dividing parts of the inferior frontal gyrus (separates pars triangularis from pars opercularis).

  • Assists in surgical orientation during neurosurgical procedures involving the frontal and temporal lobes.

  • Provides a boundary for the opercular and insular cortices.

  • Helps identify perisylvian language areas, important for language localization.

Arterial Supply

  • Supplied primarily by the superior division of the middle cerebral artery (MCA).

  • The M2 segments of the MCA run within the Sylvian fissure and give off branches to adjacent frontal and insular regions.

  • Small perforating arteries also arise from the MCA supplying the opercular cortex and adjacent white matter.

Venous Drainage

  • Drained mainly by the superficial middle cerebral vein (Sylvian vein), which runs along the Sylvian fissure.

  • Venous tributaries from the adjacent frontal and temporal opercula drain into this vein.

  • Ultimately, the venous blood is directed towards the cavernous sinus and sphenoparietal sinus.

MRI Appearance

  • T1-weighted:

    • The Sylvian fissure, including its anterior horizontal ramus, appears as a hypointense (dark) CSF-filled space separating the high-intensity (gray/white matter) brain tissues.

  • T2-weighted:

    • The fissure is hyperintense (bright) due to CSF, making the anterior horizontal ramus clearly visible as a bright linear cleft.

  • FLAIR:

    • The anterior horizontal ramus is visualized as a dark (hypointense) line since CSF is suppressed on FLAIR, enhancing the contrast with adjacent cortical tissue.

CT Appearance

  • Appears as a low-attenuation (dark) linear cleft in the lateral aspect of the brain, anterior to the main Sylvian fissure stem.

  • Readily visible on non-contrast CT as a gap between the frontal and insular opercula.

MRI images

anterior horizontal ramus of Sylvian fissure MRI 3T axial image

MRI images

anterior horizontal ramus of Sylvian fissure MRI 3T sagittal image