Spinal stenosis is an abnormal narrowing of the spinal column that may occur in any of the regions of the spine. The most common forms are cervical spinal stenosis, at the level of the neck, and lumbar spinal stenosis, at the level of the lower back. Thoracic spinal stenosis, at the level of the mid-back, is much less common. Spinal stenosis has been described as severe if the thecal sac has a cross-sectional area of less than 0.7 cm, and as moderate if the area is between 0.7 and 1 cm.