Comparison of CT myelography performed in the prone and supine positions in the detection of cervical spinal stenosis

Aim: To quantify the change in the cross-sectional area of the cervical spinal cord and subarachnoid space (SAS) in the supine neutral vs prone extension positions in patients with myelopathy undergoing cervical CT myelography. Material and Methods: Axial CT myelgrams of 21 myelopathic patients were performed in both the supine neutral and prone extension positions. The SAS and cord cross-sectional areas were then measured at the disk spaces and mid-pedicle levels from C2 to T1 in both the supine and prone positions using a public domain NIH Image program, version 156b18. Mean area measurements in both positions were then compared for each level examined. Results: Mean SAS cross-sectional area in the prone position was notably reduced compared with the supine position at C4-C5 [128.8 mm² vs 168.1 mm² (P <.05)], and C5-C6 [98.8 mm² vs 143.2 mm² (P < .05)] disk levels. The mean cord cross-sectional area failed to change significantly with positioning. Conclusions: Prone myelography may demonstrate a greater degree of cervical spine stenosis compared with CT myelography performed in the supine position in myelopathic patients. Imaging with the patient prone with neck extended in both myelography and CTM may improve precision in the results of measurements of the stenotic spinal canal when comparing these two methods.