Spinal Anatomy in Section

In cross-section the spine displays the vertebrae and intervertebral discs, the spinal canal with the cord and its coverings, and the exiting nerve roots within the neural foramina. MRI is particularly suited to the soft-tissue contents of the canal, while CT excels at the bony vertebral elements, each modality complementing the other across axial and sagittal planes.

Definition

Spinal sectional anatomy is the slice-by-slice arrangement of the vertebrae, intervertebral discs, spinal canal, spinal cord and nerve roots, meninges, and paraspinal soft tissues as displayed on axial and sagittal cross-sectional images.

Scope

The topic covers normal sectional anatomy of the vertebral column and its contents: the vertebral bodies and posterior elements, intervertebral discs, the spinal canal, the spinal cord and cauda equina, the meninges and cerebrospinal fluid spaces, the nerve roots and neural foramina, and the paraspinal soft tissues, as displayed on standard imaging planes. It is reference and educational orientation to normal anatomy, not a guide to interpreting disease.

Core questions

• How do the vertebra, disc, spinal canal, and neural foramina appear on axial and sagittal sections?
• How are the spinal cord, cauda equina, and cerebrospinal fluid spaces distinguished?
• How do CT and MRI differ in displaying the bony and soft-tissue components of the spine?

Key concepts

• Vertebral body and posterior elements
• Intervertebral disc
• Spinal canal and epidural space
• Spinal cord, conus medullaris, and cauda equina
• Meninges and thecal sac
• Nerve roots and neural (intervertebral) foramina
• Facet (zygapophyseal) joints
• Paraspinal soft tissues

Mechanisms

On an axial section through a typical vertebra the body lies anteriorly and the neural arch encloses the spinal canal posteriorly, with the pedicles, laminae, transverse and spinous processes, and the facet joints forming a recognizable ring; the disc, when sectioned at its level, lies between adjacent bodies, and the nerve roots pass through the neural foramina at the sides of the canal. Within the canal the cord (in the upper spine) or the cauda equina (below the conus medullaris) is surrounded by cerebrospinal fluid within the thecal sac and by the epidural space. Sagittal images show the alignment of the vertebral bodies and discs and the longitudinal course of the cord and thecal sac. MRI distinguishes the cord, cerebrospinal fluid, discs, and marrow by their signal and is the principal tool for canal contents, whereas CT, distinguishing structures by density, best displays the cortical and trabecular bone of the vertebrae.

Clinical relevance

Recognizing normal spinal sectional anatomy is prerequisite to reading spine CT and MRI, which are central to evaluating the vertebral column, canal, and nerve roots. This entry describes normal anatomy for educational orientation and is not guidance for diagnosis or treatment.

Evidence & guidelines

Sectional anatomy of the spine is documented in comprehensive anatomy texts and imaging atlases, which describe the normal appearance of the vertebrae, discs, canal contents, and neural foramina on standard axial and sagittal planes.

History

Cross-sectional study of the spine advanced with computed tomography in 1973 for the bony column and was transformed for the soft-tissue contents of the canal by magnetic resonance imaging, introduced by Lauterbur the same year, which made the cord, nerve roots, and discs directly visible without contrast injected into the cerebrospinal fluid.

Key figures

• Paul Lauterbur
• Godfrey Hounsfield

Seminal works

• lauterbur-1973
• hounsfield-1973
• weir-abrahams-2017

Frequently asked questions

Why is MRI preferred for the contents of the spinal canal?

MRI distinguishes the spinal cord, cerebrospinal fluid, nerve roots, and intervertebral discs by their signal characteristics and images them directly in any plane, whereas CT is better suited to the bony vertebral elements.

Where does the spinal cord end on a sagittal image?

The cord tapers at the conus medullaris in the upper lumbar region, below which the canal contains the cauda equina, a bundle of nerve roots surrounded by cerebrospinal fluid within the thecal sac.