What is panna? Is it permanent?

Because panna (wisdom) is the understanding of anicca, dukkha and anatta, it leads to the cessation of ignorance, greed and aversion and therefore to Nirvana. Now Nirvana or the state of being enlightened is permanent, so panna must be too, mustn't it? The cessation of ignorance alone is not enough, because it could rise again, couldn't it? I mean it already happened one time...

So to hinder ignorance from rising again, panna must be permanent. This is how I always understood it. I always thought of it as an aspect of Nirvana, and therefore not a part of the impermanent (?) skandhas.

Now I read a text which says that panna is a sankhara. Aren't sankharas as the 4th skandha impermanent and cease to exist when entering Paranirvana?

So what is panna?

Thank you.