Craniocervical Junction Abnormalities By Michael Rubin, MDCM, New York Presbyterian Hospital-Cornell Medical Center Reviewed / Revised Jan 2022 | Modified Sep 2022 View Patient Education Etiology Symptoms and Signs Diagnosis Treatment Key Points Topic Resources Basilar Invagination (MRI) Basilar Invagination and... Atlantoaxial Subluxation Atlantoaxial Subluxation... Halo Ring Halo Brace Craniocervical junction abnormalities are congenital or acquired abnormalities of the occipital bone, foramen magnum, or first two cervical vertebrae that decrease the space for the lower brain stem and cervical cord.