Trolls as nodes or random events?

[Mateusz_Zboj]

I've heard that troll spawn in normaly invisible caves that can be dug out and work similar to nodes.
So would that mean that if i am digging last one tile inside of ring of already dug mine there would be no chance of getting a troll? Or are they rather random events that can pop from single tile?

[DDDsDD999]

loftar wouldn't tell us.

[Mateusz_Zboj]

But some might !!scientists!! surely found something out. The question is, are they willing to share their knowledge with us?

[Zachary09]

The matter described in OP is to be found out by for example Xcom, so far people believe the trolls are a random encounter. So far during my game i have encountered only a single troll on layer 3.