Spinal radiation anatomy

Basic structure and the three-column concept

Each vertebra (except for the first cervical vertebra) consists of an anterior mass — the vertebral body (corpus vertebrae) — and a posterior part called the neural arch (arcus posterior). Together, these structures form a bony ring that encloses the vertebral canal.

To assess spinal stability in trauma and disease, diagnostic imaging utilizes a functional division into three supporting columns:

• Anterior column: includes the anterior longitudinal ligament, the anterior part of the anulus fibrosus, and the anterior two-thirds of the vertebral body.
• Middle column: consists of the posterior third of the vertebral body, the posterior aspects of the anulus fibrosus, and the posterior longitudinal ligament.
• Posterior column: combines all posterior bony elements (pedicles, laminae, articular and spinous processes) along with the posterior ligamentous apparatus.

Visualization of the vertebral body and bone marrow

The vertebral body is formed by a thin cortical shell and central cancellous bone with vertically oriented trabeculae. CT clearly demonstrates the bony structure and vascular channels (which must not be confused with fractures), as well as sclerotic bands at the sites of fusion of ossification centers (e.g., remnants of the subdental synchondrosis in the dens of the axis).

Evaluation of the bone marrow is optimally performed using MRI (on T1-weighted images). Bone marrow is a dynamic tissue that changes with age as red (hematopoietic) marrow is replaced by yellow (fatty) marrow. Several Ricci patterns are distinguished:

1. Pattern 1: Homogeneous low signal with a bright line around the basivertebral vein. Characteristic of young individuals (under 30 years).
2. Pattern 2: Band-like high signal along the periphery of the vertebral body (typical for middle age).
3. Pattern 3: Multiple small, ill-defined foci of high signal throughout the body (age 40 and older).
4. Pattern 4: Appearance of large hyperintense areas (5–15 mm), typical for the elderly.

Joints and intervertebral discs

Facet (zygapophyseal) joints are true synovial joints. In the lumbar spine, their articular surfaces are oriented obliquely (at an angle of about 45 degrees), whereas in the thoracic spine they are nearly frontal. The inferior facets are convex, and the superior facets are concave. An interesting feature of the joint capsule is the absence of a fibrous layer anteriorly, where the ligamentum flavum serves as the joint boundary. Fat pads are located within the recesses of the capsule, acting as shock absorbers and lubricants.

Uncovertebral joints (joints of Luschka) are found only at the C3–C7 levels. They are formed by the uncinate processes of the vertebral bodies, protect against lateral disc herniations, and allow cervical rotation.

Intervertebral disc is a symphysis:

• Inner part—nucleus pulposus (nucleus pulposus). Develops from notochordal cells, rich in water and proteoglycans (undergoes dehydration with age).
• Outer part—anulus fibrosus (annulus fibrosus). Its outer layers (Sharpey's fibers) are firmly woven into the bone tissue of the vertebral bodies and longitudinal ligaments.

Ligamentous apparatus and spinal canal

The stability of the spinal column is maintained by a robust ligamentous system:

• Anterior longitudinal ligament (ALL): runs along the anterior surface of the vertebral bodies, widening at the disc levels.
• Posterior longitudinal ligament (PLL): lies within the spinal canal. At the level of the vertebral bodies, it is separated from the bone by the anterior epidural space (where basivertebral veins run).
• Ligamentum flavum (ligamentum flavum): a paired elastic ligament connecting the vertebral laminae and forming the posterior wall of the spinal canal. It fuses laterally with the capsule of the facet joints.
• Interconnecting ligaments: supraspinous, interspinous, and intertransverse ligaments—connect the respective processes.

The shape of the spinal canal transitions from oval (in the cervical and thoracic regions) to triangular (in the lumbar region). The dura mater is in close contact with the PLL anteriorly. In the thoracic spine (against the background of kyphosis), up to 5 mm of epidural fat may normally accumulate between the dural sac and the posterior elements—this is a normal variant rather than epidural lipomatosis.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Radiological landmarks (I, L, O, P, S, Sp, T) on spinal radiographs
• Embryology and histogenesis of the nucleus pulposus of the disc
• Anatomy and contents of the anterior epidural space
• Detailed imaging anatomy of C1 and C2 (atlas and axis)

Other topics in the "Spine" section

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