What are the three main types of disc contour abnormalities?

1. Bulge. This is broad based and usually with an intact annulus fibrosis.
2. Protrusion. This is more focal, with a narrower base than in a bulge. The base is still wider than the apex. It is associated with annular tearing.
3. Extrusion. Components of the nucleus pulposus extend beyond the annulus (base is narrower than apex).