CRANIOVERTEBRAL JUNCTION - NORMAL ANATOMY, CRANIOMETRY, AND CONGENITAL-ANOMALIES

The craniovertebral junction (CVJ) comprises the occiput, atlas, and a xis and is visible in most: magnetic resonance (MR) imaging studies of the brain. Craniometric measurements used in radiologic assessment of CVJ anomalies include the Chamberlain line, Wackenheim clivus baselin e, Welcher basal angle, and atlantooccipital joint axis angle. Most an omalies of the occiput are associated with decreased skull base height and basilar invagination, the latter being a primary developmental an omaly in which the vertebral column is abnormally high and prolapsed i nto the skull base. Occiput anomalies include condylus tertius, condyl ar hypoplasia, basiocciput hypoplasia, and atlantooccipital assimilati on. Most atlas anomalies produce no abnormal CVJ relationships and are not associated with basilar invagination. These anomalies include apl asias, hypoplasias, and clefts of the atlas arches and ''split atlas'' (ie, posterior arch rachischisis associated with anterior arch rachis chisis). Except for fusion anomalies, abnormalities of the axis are pr imarily confined to the odontoid process and are not associated with b asilar invagination. These anomalies include persistent ossiculum term inale, odontoid aplasia, and os odontoideum. With the widespread avail ability of MP imaging, which is well suited for evaluating the CVJ bec ause of its direct sagittal imaging capabilities, renewed understandin g of CVJ anatomy and anomalies is important for all radiologists.