What are world rune fragments?

In Ryze's comic, this conversation between Kala and Ryze takes place:

Kala: What is it what we seek? And why is it here? Ryze: A fragment of one of the primordial world runes.

Yet, as far as I'm aware that is the only reference to 'world rune fragments' in the entire lore. In every other instance they are just referred to as 'world runes'. Usually Riot is quite careful with their lore, so I doubt the 'fragment' was just thrown in there haphazardly.

That leads to the question, Did much more powerful runes, called 'primordial world runes' exist and are the current world runes just shards of them? Would it be possible to put the pieces back together to create a primordial world rune?