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Groove for vertebral artery

he groove for the vertebral artery is a shallow sulcus located on the superior surface of the posterior arch of the atlas (C1). It serves as the bony channel in which the vertebral artery, vertebral venous plexus, and C1 spinal nerve course before entering the foramen magnum.

The groove represents a critical transitional point where the vertebral artery curves medially after ascending through the transverse foramina. Its position on the posterior arch provides protection while allowing vascular flexibility during head rotation and extension.

Synonyms

  • Sulcus arteriae vertebralis

  • Vertebral artery groove

  • C1 arterial sulcus

Location and Structure

  • Situated on the superior posterior arch of C1, lateral to the midline.

  • Forms a smooth, shallow concave bony depression accommodating the vertebral artery.

  • May occasionally convert into a complete foramen (arcuate foramen) if bridged by a bony arch.

  • Serves as the final extradural segment of the vertebral artery before it pierces the dura.

Relations

  • Superiorly: Suboccipital region, musculature of the posterior neck

  • Inferiorly: Posterior arch of C1

  • Medially: Midline posterior tubercle of atlas

  • Laterally: Lateral mass of C1

  • Anteriorly: Atlas ring and atlanto-occipital membrane

  • Posteriorly: Suboccipital nerve and deep cervical musculature

Attachments

  • The atlanto-occipital membrane attaches adjacent to the groove, forming a partial fibrous roof.

  • Muscular attachments nearby include fibers of rectus capitis posterior major/minor and obliquus capitis superior, though none attach directly inside the groove.

Function

  • Provides a protective bony channel for the vertebral artery before it enters the cranial cavity.

  • Allows space for the artery to curve and accommodate head rotation and extension.

  • Serves as an anatomical landmark in cervical spine imaging and posterior approach surgeries.

MRI Appearance

T1-weighted images

  • Groove cortex: low signal (dense cortical bone)

  • Marrow of posterior arch: bright fatty signal

  • Vertebral artery within groove: typically a dark flow void

  • Surrounding soft tissues: intermediate signal representing suboccipital muscles

T2-weighted images

  • Cortical bone: dark

  • Marrow of posterior arch: bright relative to cortex

  • Arterial flow: dark flow void

  • Suboccipital soft tissues: intermediate-to-bright signal

STIR

  • Cortical bone: dark

  • Bone marrow: intermediate-to-dark

  • Soft tissues: intermediate signal

  • Fluid-sensitive highlighting of fascial planes around the groove

T1 Fat-Saturated Post-Contrast

  • Bone: no enhancement

  • Vertebral artery lumen: bright enhancement

  • Surrounding soft tissues: mild enhancing interfaces adjacent to dura or membranes

  • Atlanto-occipital membrane: thin enhancing line adjacent to groove

CT Appearance

Non-Contrast CT

  • Groove appears as a shallow, smooth, sharply defined depression along superior posterior arch of C1

  • Cortical margins: high-attenuation dense bone

  • Marrow: lower attenuation relative to cortex

MRI images

Groove for vertebral artery