A bulge is a bulge in the annulus and ligament, much like a bump on a rubber ball that has been weakned... it's still intact, but compromised, so there is a bump.
A protrusion is where the disc annulus (like the outside of a jelly donut or the rubber exterior of a tire) is torn all the way through and some disc nucleus material (jelly of the donut), is extruded through the annulus and possibly the ligament too.
Mark
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