- 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)
It is 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. If the extrusion migrates but becomes separated from the rest of the herniation it is known as a disc sequestration.
- 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