Traumatic vertebral artery dissections tend to occur where the vertebral artery crosses bony prominences, e.g. at the atlantoaxial junction or where it enters the foramen transversarium (usually at C6). Spontaneous dissections tend to be intracranial and commonly occur on the dominant VA. Unlike cervical ICA dissections, which tend not to propagate intracranially through the carotid canal, high cervical VA dissections can readily propagate intracranially through the foramen magnum.