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Lateral groove of midbrain

The lateral groove of the midbrain, also known as the lateral mesencephalic sulcus, is a longitudinal surface groove located on the lateral aspect of the midbrain. It represents an important anatomical landmark where specific brainstem structures emerge and where vascular and neural elements course along the midbrain surface.

This groove is particularly notable for its relationship to cranial nerve pathways and for its value in surface anatomy, neuroanatomical orientation, and imaging correlation.

Synonyms

  • Lateral mesencephalic sulcus

  • Lateral sulcus of the midbrain

Location

  • Located on the lateral surface of the midbrain

  • Extends longitudinally between the cerebral peduncle and the midbrain tegmentum

  • Runs from the level of the inferior colliculus inferiorly toward the pontomesencephalic junction

  • Forms part of the transition zone between ventral and dorsal midbrain structures

  • Seen bilaterally and symmetrically on the midbrain surface

Anatomical features

  • Surface groove:

    • Shallow longitudinal depression

    • Does not contain cortical gray matter

  • Neural relationship:

    • Close association with fibers of the trochlear nerve (CN IV) as they wrap around the midbrain

  • Vascular relationship:

    • Small perforating vessels may course nearby

Relations

Anteriorly:

  • Cerebral peduncle (crus cerebri)

Posteriorly:

  • Midbrain tegmentum

Superiorly:

  • Inferior colliculus region

Inferiorly:

  • Pontomesencephalic junction

Laterally:

  • Ambient cistern

Medially:

  • Periaqueductal gray (deep to the surface)

Associated nerves

  • Trochlear nerve (CN IV):

    • Emerges dorsally from the midbrain

    • Wraps around the lateral surface of the midbrain

    • Courses along or near the lateral groove before entering the cavernous sinus

Function

  • Anatomical landmark: Assists in identifying surface orientation of the midbrain

  • Neurovascular corridor: Provides a surface pathway for cranial nerve IV and adjacent vessels

  • Surgical relevance: Used as a reference point in lateral midbrain and ambient cistern approaches

MRI appearance (normal)

T1-weighted images:

  • Lateral groove: Appears as a subtle linear indentation on the lateral midbrain surface

  • Signal: Follows adjacent brainstem parenchyma signal

  • Best visualized on high-resolution axial  images

T2-weighted images:

  • Normal groove: Thin CSF-filled contour outlining the midbrain surface

  • Midbrain parenchyma: Low-to-intermediate signal intensity

FLAIR:

  • Normal: CSF suppression highlights the surface contour of the groove

  • Groove visibility: Enhanced by contrast between brainstem and ambient cistern

Diffusion-weighted imaging (DWI):

  • Normal: No diffusion restriction

Post-contrast T1-weighted images:

  • Normal: No intrinsic enhancement of the groove

CT appearance (normal)

Non-contrast CT:

  • Lateral groove: Not directly visualized

MRI image

MRI Lateral groove of midbrain anatomy image -img-00000-00000_00001