is important in platybasia/basilar impression descrip­tion as it is not unusual for this angle to become rather acute (even 90°) sometimes without abnormal violation of the above described Wackenheim clivus baseline. Due to common difficulties with visualization of bony structures required for the measurement of clivus-canal angle, particularly after decompressive procedures and the indirect nature of bony parameters attempting to represent neurological compromise, Bundschuh et al. described cervico-medullary angle (CMA) in order to directly demonstrate the degree of brainstem and spinal cord compression in basilar invagination or cranial set­tling in rheumatoid patients [5]. They compared those values with 50 normal patients and concluded that all patients with CMA of less than 135° had evidence of brainstem compression, cervical myelopathy, or C2 nerve root pain. The angle is measured at the intersec­tion of lines drawn parallel to ventral surfaces of the medulla and upper cervical cord on MRI (Fig. 3.5). Multiple publications since then have correlated the CMA with clinical syndrome as well as therapeutic indications and outcomes [39, 54]. However, the largest study defining the normal values of CMA found it to be approximately 158° (139°–175° range) when evaluating 200 patients’ MRI without craniovertebral anomalies [53]. Furthermore, the authors also found the CMA to have an excellent inter- and intra-observer reliability.