The Anatomy of the Thoracic Spinal Canal in Different Postures: a Magnetic Resonance Imaging Investigation

Background And Objectives: The goal of this study was to investigate,with magnetic resonance imaging, the human anatomic positions of the spinal canal (eg, spinal cord, thecal tissue) in various postures and identify possible implications from different patient positioning for neuraxial anesthetic practice.

Method: Nine volunteers underwent magnetic resonance imaging in supine, laterally recumbent, and sitting (head-down) positions. Axial and sagittal slices of the thoracic and lumbar spine were measured for the relative distances between anatomic structures, including dura mater and spinal cord.

Results: The posterior dura-spinal cord (midline) distance is on average greater than the anterior dura-spinal cord (midline) distance along the thoracic spinal column, irrespective of volunteer postures (P G 0.05).The separation of the dura mater and spinal cord is greatest posterior in the middle thoracic region compared with upper and lower thoracic levels for all postures of the volunteers (P G 0.05). By placing the patient in a head-down sitting posture (as commonly done in epidural and spinal anesthesia), the posterior separation of the dura mater and spinal cordis increased.

Conclusions: The spinal cord follows the straightest line through the imposed geometry of the spinal canal. Accordingly, there is relatively more posterior separation of the cord and surrounding thecal tissue at midthoracic levels in the apex of the thoracic kyphosis. Placing a patient in a position that accentuates the thoracic curvature of the spine (ie,sitting head-down) increases the posterior separation of the spinal cord and dural sheath at thoracic levels.