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Left vertebral artery (atlantic part)

The left vertebral artery (atlantic part), also known as the V3 segment, is the portion of the vertebral artery that courses from the transverse foramen of C2 to its entry into the foramen magnum at the atlanto-occipital junction. It forms a loop around the lateral mass of the atlas (C1) and passes posterior to the lateral mass, anterior to the posterior arch, before piercing the dura and entering the cranial cavity. This segment is tortuous to accommodate head rotation and is particularly vulnerable to trauma, dissection, or compression.

It is a key vessel supplying posterior circulation, including the cerebellum, brainstem, and posterior cerebral hemispheres, and contributes to the formation of the basilar artery after joining its contralateral counterpart. The atlantic part is stabilized by surrounding muscles (suboccipital muscles) and ligaments, yet its anatomical course allows for some physiological mobility during neck movements.

Function

  • Supplies posterior cerebral circulation

  • Provides blood flow to cerebellum, brainstem, and posterior cerebral hemispheres

  • Forms part of the basilar artery with the contralateral vertebral artery

  • Maintains adequate perfusion during cervical motion

Synonyms

  • Vertebral artery V3 segment

  • Atlantic part of vertebral artery

  • Suboccipital vertebral artery segment

MRI Appearance

T1-weighted images:

  • The vessel lumen appears as intermediate to low signal intensity tubular structure within the surrounding soft tissues

  • Flow void may be present if high-velocity blood flow is present, appearing as signal loss

  • Vessel walls are usually not distinctly visible, unless thickened or pathologically altered

T2-weighted images:

  • Lumen may show signal void due to fast flow (“flow void”), surrounded by muscle and fat of the suboccipital region

  • Vessel wall remains low signal; surrounding edema or hematoma may appear hyperintense in pathological conditions

Time-of-Flight (TOF) or MR Angiography:

  • Vessel appears bright (hyperintense) due to flow-related enhancement, allowing precise delineation of course, loops, and stenosis

  • Tortuous atlantic segment is clearly visible

  • Useful for detecting dissection, stenosis, aneurysms, or occlusion

T1 Post-Contrast (Gadolinium-enhanced):

  • Vessel lumen enhances brightly, allowing assessment of stenosis, dissection, or vascular malformations

  • Vessel wall enhancement may indicate inflammation or pathological changes

CT Appearance:

  • On CT angiography, the vessel is seen as a hyperdense tubular structure with clear course from C2 transverse foramen to foramen magnum

  • Tortuous loop over the atlas is visualized in axial, coronal, and sagittal planes

  • Surrounding bony landmarks (C1 lateral mass, posterior arch) provide anatomical orientation

  • Useful for evaluating vertebral artery injury, stenosis, or congenital anomalies

MRI images

Left vertebral artery (atlantic part) mri axial image