- in at least one plane, has a broader dome (B) than a neck (A)
- extends above or below the disc level (into the suprapedicular or infrapedicular zone)
Disc extrusions are associated with a defect in the annulus fibrosus which allows herniation of nucleus pulposus beyond the confines of the disc. Depending on imaging method, the distinction between extrusion and protrusion may be difficult, in such cases, the general expression "disc herniation" may be used.
Extrusion can be in any axial direction and may migrate either superiorly or inferiorly.
- disc protrusion is distinguished form a disc extrusion in that the base of protruded disc material base is narrower than its 'dome'; furthermore this material may extend above or below the disc level.
- disc sequestration is an extrusion where the disc material migrates and becomes separated from the rest of the herniation.
A number of definitions of what exactly constitutes a disc protrusion have been proposed over the years, and it is important to realise that these differ substantially from one another 1-4. At the time of writing (August 2016) the most recent and widely used terminology was proposed in 2014 by Fardon et al, and represents a consensus of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology 4.
- spinal anatomy
- congential abnormalities of the spine
- spinal infection / inflammation / degeneration
- intervertebral disc
- intervertebral disc disease nomenclature
- lumbar disc disease
- acute calcific discitis
- acute disseminated encephalomyelitis (ADEM)
- Charcot-Marie-Tooth disease
- HIV vacuolar myelopathy
- HTLV-1 associated myelopathy (tropical spastic paraparesis)
- multiple sclerosis
- neuromyelitis optica (NMO) - (Devic's disease)
- transverse myelitis
- SCA3 (Machado-Joseph disease)
- subacute combined degeneration of the cord
- subacute necrotizing myelopathy
- tabes dorsalis
- spinal ischaemia
- spinal trauma
- spinal tumours and cysts
- spinal vascular malformations
- 1. Fardon DF, Williams AL, Dohring EJ et-al. Lumbar disc nomenclature: version 2.0: Recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology. Spine J. 2014;14 (11): . doi:10.1016/j.spinee.2014.04.022 - Pubmed citation