A disc protrusion and extrusion are a type of herniated disc. The only difference between them is the shape. A protrusion is shaped like a bush from the ground; the bottom layers are wider than the top. A disc extrusion is the opposite and is similar to a tree; the end of the herniation is much wider than the closer base or ‘stem’.
The difference matters because they tend to represent 2 patterns of herniations. A disc protrusion is when all layers of the outer annulus fibrosus herniated outwards. On the other hand, a disc extrusion is when only the inner nucleus pulposus herniates through a tear in annulus fibrosus.