MRI measurements of the cervical spine and their correlation to Pavlov's ratio

Study Design. Pavlov's ratio from plain radiographs in patients with neck pain but no radicular symptoms was compared with the areas of the cervical spinal cord and cerebrospinal fluid column on magnetic resonance scans. Summary of Background Data. The area of the cervical canal or cord obviously depends on both the sagittal and transverse diameters. Although the pathology in stenosis of the cervical spine is mainly in the sagittal plane, narrowing only in the sagittal diameter may not indicate significant reduction in the area of the canal. The transverse area of the cord has been shown to correlate well with the pathologic changes of the cord in cervical myelopathy. We correlated Pavlov's ratio on the plain radiographs to the area of the cerebrospinal fluid column and the area of the cord on the magnetic resonance scan. Methods. We examined the lateral radiographs and axial and sagittal T2-weighted magnetic resonance scans in the neutral position of the cervical spine (C4-C7) of 87 patients with 332 levels with neck pain but no radicular symptoms and normal magnetic resonance scans. On the magnetic resonance images, the sagittal diameters of the cerebrospinal fluid column and the cord were measured at the midvertebra level on T2 sagittal images from C4 to C7. From the T2 axial images, the area of the cord and the area of the cerebrospinal fluid column were measured at the same levels. Results. The correlation between Pavlov's ratio and the area of cerebrospinal fluid column was moderate, with the highest value of 0.31 at C5. The sagittal diameter of the cerebrospinal fluid column showed variable correlation with the area of the cerebrospinal fluid column. The highest correlation was 0.68 between the sagittal diameter and the area of the cerebrospinal fluid column at C7. The correlation between Pavlov's ratio and the area of the cord is around zero, with the highest correlation of 0.21 at C4. The sagittal diameter of the cord showed a moderate correlation with the area of the cord. Conclusion. This study shows a poor correlation between Pavlov's ratio and the space available for the cord. Therefore, this ratio cannot be solely relied upon to predict the area changes in that plane of the cervical spinal canal.