Chapter 14: The Thoracolumbar Spine

INTRODUCTION

Images of normal anatomy reveal the typical lumbar spine consisting of five lumbar vertebrae, featuring rectangular bodies. From a lateral view or in sagittal slices, the interposed disks increase in height with caudal progression, although the L5-S1 disk is variable.

Of principal importance is the general contour of the spine. The curvilinear alignment of the vertebrae is represented on a lateral view or sagittal slices (Figures 14-1 and 14-2):

1. A line spanning the anterior margins of the vertebral bodies: anterior spinal line.

2. A line adjoining the posterior margins of the vertebral bodies: posterior spinal line.

3. The line adjoining the junctions of the laminae and the anterior margins of the spinous processes: spinolaminar line.

4. A line along the tips of the spinous processes: spinous process line.

In axial images, the posterior margins of the disks and vertebral bodies are concave, contributing to a usually triangular spinal canal (Figure 14-3). The posterior aspect of the L5-S1 disk can again be less consistent in its contribution to this form. With caudal progression in the lumbar spine, the interpedicular distance increases.

In the thoracic spine, many of the same elements exist as in the lumbar region, including increasing vertebral body size with caudal progression. The intervertebral disks, however, are proportionally smaller within the motion segments. The interpedicular distance decreases from T1 to T6, then increases again through T12.

The ligamentous and neural structures of the thoracic and lumbar spines are demonstrated most clearly on magnetic resonance imaging (MRI). The bony apertures for the neural structures are best seen by computed tomography (CT) or MRI, as are the pars interarticulares and the facet joints.

The spinal cord in the thoracic region has a round to oval cross section, expanding normally at the conus, the tip of which is usually at L1 or L2. The appearances of the thoracic and lumbar spines on MRI are dependent on age as changes in the marrow of the vertebral bodies occur in adulthood. Similarly, the proportion of nuclear material with the disk reduces with maturity.

On T1-weighted MRI, the cerebrospinal fluid is of low signal intensity in contrast to the intermediate signal from ...