Medullary cone movement in subjects with a normal spinal cord and in patients with a tethered spinal cord

PURPOSE: To compare movement of the normal medullary cone when the patient has changed from a supine to prone position with that in patients with know n or suspected tethered spinal cord syndrome. MATERIALS AND METHODS: Fifty-six individuals divided into three groups were examined with lumbar spine magnetic resonance (MR) imaging performed with the patient in the prone and supine positions. Group 1 consisted of 15 heal thy volunteers and six patients with a herniated disk; group 2, 25 patients clinically suspected of having a tethered cord; and group 3, 10 patients w ho previously had undergone tethered cord surgery. RESULTS: All group 1 subjects showed distinct and statistically significant medullary cone movement (range, 21%-41%); no patient in group 3 showed mov ement (Wilcoxon rank sum test, P < .001). in group 2, the 20 patients in wh om a definite diagnosis of tethered cord syndrome was made on the basis of initial supine MR image findings showed no movement, whereas two of five pa tients with normal supine MR images had abnormal and decreased cone movemen t at prone imaging. CONCLUSION: Prone MR imaging has no additional value when the supine MR ima ge has clearly shown the cause of tethering Or in patients who have undergo ne tethered cord surgery, but it can provide additional information in pati ents clinically suspected of having a tethered cord and in whom supine MR i maging depicted no abnormalities.