- 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 from a disc extrusion in that the base of protruded disc material is wider than its 'dome'; furthermore this protruded disc material must not 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.
Note: a number of definitions of what exactly constitutes a disc protrusion have been proposed/used over the years, and it is important to realize 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.
- 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
- 2. Yi JS, Cha JG, Han JK, Kim HJ. Imaging of Herniated Discs of the Cervical Spine: Inter-Modality Differences between 64-Slice Multidetector CT and 1.5-T MRI. (2015) Korean journal of radiology. 16 (4): 881-8. doi:10.3348/kjr.2015.16.4.881 - Pubmed
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