Anatomy of the adult vertebral body vascular network
Anatomy of discovertebral junction is complex,
including components of anterior and posterior elements of the spine. The anterior elements include the intervertebral discs,
Sharpey´s fibers,
vertebral body,
vertebral endplates and anterior and posterior longitudinal ligamentous complex. The posterior elements are made up of the facet joints and pars interarticulares,
as well as the pedicles,
lamina,
transverse processes and spinous processes.
The anatomy of the adult vertebral body vascular network is important in understanding the typical pattern of infection.
The arterial contribution to each vertebral body consist of paired segmental arteries that arise from vertebral arteries,
the aorta or the iliac arteries.
The vessel curves posterolaterally in front of the vertebral body and sends small branches into its marrow and multiple extraosseous anastomotic channels.
In adulthood,
the blood supply of the spine is of terminal type and arteries have end vessels at the superior and inferior endplates of the vertebral bodies whereas in childhood,
the arterial network extends to intervertebral disc.
The vertebral columns is drained by networks of veins.
These venous plexuses are formed by spinal veins along the vertebral column and include internal and external vertebral venous plexuses.
Pathophysiology of spinal infections
Infection of the spinal column or osteomyelitis of the spine is rare,
and often recognized and treated too late.
There are three main infection routes that may contribute to the development of spinal infection.
- Hematogenous
- Direct external bacterial inoculation
- Extension from a contiguous infectious site
Haematogenous spread,
and more often via arterial network than venous,
is the most common source of infection,
representing the 60-70% of adult osteomyelitis cases.
The primary focus of infective change usually begins in the anterior subchondral region adjacent to the end plate where the blood suply is particularly evident.
The subsequent spread of infection to the contiguous disc and vertebra creates the characteristic lesion of spondylodiscitis.
Magnetic resonance imaging findings of infectious spondylitis
The clinical presentation is often vague and nonspecific and the diagnosis should be supported by an imaging study,
being MRI the most sensitive imaging test.
The standard MRI examination should include axial and sagittal FSE T1-weighted (T1WI),
T2-weighted (T2WI),
short-tau inversion recovery (STIR) and fat-suppressed T1-weighted with gadolinium sequences.
The earliest signs of an infective process on MR imaging are low marrow signal on T1WI and high signal on fluid-sensitive images,
related to oedema and hyperaemia,
with enhancement of the involved vertebral bodies after contrast medium administration.
Additionally,
MR imaging is useful in identifying evidence of either paraspinal or epidural inflammatory tissue,
peripheral enhancement of the infected disc and erosion or destruction of the vertebral endplates.