Cervicomedullary junction (CMJ), as the name implies is the region where the brainstem continues as the spinal cord. A lesion located in this region affects either the brainstem or cervical cord or both depending on its extent and pathology.

The Cervicomedullary junction CMJ reliably lies 3.4 mm (±0.9 mm) caudal to the inferior border of the olive and 6.4 mm (±1.3 mm) caudal to the obex. Awareness of this anatomic relationship readily allows recognition of abnormalities of the position of the CMJ with routine imaging ¹⁾.