The Stages and Classifications of Disc Protrusion
A disc protrusion occurs when a portion of an intervertebral disc extends beyond its normal boundary, or base. This is a general term that might apply to one of the more common terms used to describe displacement of disc material - bulging disc and herniated disc. The difference is, a herniated disc is present when material from inside the disc (nucleus pulposus) has leaked through a tear in the disc and into the spinal canal, while with a bulging disc, only the disc wall (annulus fibrosus) has become displaced.
Classifications of a Disc Protrusion
If the protruding portion of the disc is less than 90 degrees (no more than 25 percent) of the disc's circumference, it is classified as focal. If the protruding portion encompasses 90-180 degrees (between 25 and 50 percent) of the disc's circumference, it is classified as broad-based. A disc protrusion also is classified by which direction the disc material extends beyond the normal boundary, as follows:
- Lateral - protrusion to the left or right side
- Posterolateral - protrusion to the back and either the right or left side
- Central - protrusion toward the center of the spinal canal, where the spinal cord is located
- Paracentral - a less-precise description of a central protrusion that could skew to either side
- Posterior - protrusion toward the rear of the spinal canal
- Anterior - protrusion toward the front of the spine; a fairly uncommon condition that rarely produces symptoms
Stages of a Disc Protrusion
Because there is no standardized method for referring to the condition, the use of the term disc protrusion may mean one thing to one doctor, and something else to another doctor. In general, though, a herniated disc occurs in stages, starting with a reduction in water content within the disc. Eventually, the outer wall becomes brittle and weak, and pressure from the vertebrae above and below forces the outer wall out of its boundary. Sometimes, a rupture forms on the outer wall, and nucleus material begins to leak. If this material breaks free into the spinal canal, it is said to be sequestered. More often than not, this sequestered material is absorbed by the body through a process known as resorption.
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