![]() There are two main mechanisms to explain radicular pain secondary to a nucleus pulposus herniation: Mechanical compression and inflammatory reaction. Clinical symptoms may vary according to several factors such as the location of the herniation (level), neural compression, and evolution. The correct knowledge of anatomy and the relationship between nerve roots and disc herniation allows the proper understanding of common clinical findings associated with this problem. On the sagittal plane, the levels are termed as follows: The supra pedicular level, the pedicular level, the infrapedicular level, and the disc level. On the axial plane, these landmarks determine the central zone, the subarticular zone (lateral recess), foraminal, and extraforaminal zones. Wiltse proposed these anatomical zones, based on the following landmarks: medial border of the articular facet, lateral, upper and medial borders of the pedicles, coronal and sagittal planes at the center of the disc. Proper understanding of anatomical zones and vertebral levels is essential to interpret the clinical manifestations secondary to a disc herniation. One important kind of annulus fissure can be observed in T2-weighted MRI and is called high-intensity zone (HIZ), this changes denote the presence of liquid within an annular fissure and correlates with acute disc annular tear or fissure. These types of fissures are observable in the early stages of disc degeneration. The loss of annulus fibrosus integrity may be present in different forms, such as radial, transverse, or concentric fissures. The integrity of the annulus fibrosus has to be compromised to develop a nucleus pulposus herniation. Extrusion is present when, in at least one plane, the distance between the limits of the disc material beyond the disc space exceeds the distance between the limits of the base of the disc material beyond the disc space.Īnother type of disc herniation is when disc material migrates in craniocaudal direction through a gap between the endplate and the disc making a space within the vertebral body ( intravertebral disc herniation) better know as Schmorl nodes. The base is the width of disc material at the outer margin of the disc space. A protrusion is when the greatest distance between the limits of the disc material outside the disc space is less than the distance between the limits of the base of that disc material outside the disc space. Nucleus pulposus protrusion is the less severe scenario of disc herniation, due to partial rupture of the annulus fibrosis ( See figure 1), when the annulus structure becomes completely disrupted the nucleus content may extrude outside the disc space and in some cases a fragment of nucleus pulposus may migrate ( sequestration).Īnother way to differentiate protrusion from extrusion is related to the shape of the displaced material. Nucleus pulposus herniation results from a failure in the annulus fibrosis integrity, making the content of the nucleus to protrude into the neural canal, the intervertebral foramen (foraminal) or lateral to the foramen (extraforaminal).
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