Updated December 04, 2014.

Definition: Several words are used to describe the extent of a disc herniation seen on MRI examination. A disc herniation occurs when the soft cushion between the spinal bone ruptures. A portion of that disc can herniate, or push outwards, against the spinal cord or the spinal nerves. The pressure on the nerves causes the symptoms typical of a disc herniation.

The types of disc herniation that occur include:

• Disc Protrusion
  Commonly called a disc bulge, a disc protrusion occurs with the spinal disc and the associated ligaments remain in tact, but form an outpouching that can press against the nerves.
   
  
• Disc Extrusion
  A disc extrusion occurs when the outer part of the spinal disc ruptures, allowing the inner, gelatinous part of the disc to squeeze out. Disc extrusions can occur with the ligaments in tact, or damaged.
   
  
• Disc Sequestration
  A disc sequestration occurs when the center, gelatinous portion of the disc is not only squeezed out, but also separated from the main part of the disc.