What terms are used to describe the different types of disc extension beyond the vertebral body margin?
The spectrum includes disc bulge, protrusion, extrusion, and sequestration.
- • Disc bulge is diffuse extension of the intervertebral disc beyond the level of the cortical margin of the adjacent vertebral endplate, which is usually symmetric or slightly eccentric to one side and results from laxity or stretching of the annulus fibrosus. The annulus fibrosus is a ring of sturdy ligament fibers that encases the gel-like nucleus pulposus of the intervertebral disc.
- • Disc protrusion is a focal disc extension beyond the boundaries of the remainder of the disc, which is still contained within the annulus fibrosus. The neck of the protrusion is the widest portion of the abnormality.
- • Disc extrusion is a focal disc extension in which its neck is narrower than the extruded portion of the disc, indicating extrusion through an annular fissure. Extrusions often extend superiorly or inferiorly as well along the long axis of the spinal canal.
- • Disc herniation is a generic term that encompasses both disc protrusion and extrusion.
- • Disc sequestrum or sequestration is a free fragment of the intervertebral disc, which has extruded through the annulus fibrosus and separated from the remainder of the disc to lie within the epidural space.
- • Location: The location of a disc herniation determines what nerve roots are affected. Central, right central/left central/right paracentral/left paracentral, subarticular, foraminal, and extraforaminal/far lateral describe the location. Right or left central (or paracentral) and subarticular (lateral recess) locations affect the ipsilateral traversing nerve root. The foraminal or extraforaminal disc herniation affects the exiting nerve root.