CT in nonvisualised vertebral levels caudal to the complete block on lumbar myelogram.

CT was performed in 51 patients at and caudal to the level of lumbar myelographic block due to disc herniation with or without lumbar canal stenosis. The causes of complete or almost complete myelographic block included disc herniation (27 patients)disc herniation with spinal stenosis (12 Patients), spinal canal stenosis (11 patients) and posterior osteophytes (1 patient). CT helped in detecting the non-visualised vertebral levels, demonstrated a surgically treatable lesion below the level of myelographic block and provided information for preoperative planning.