Idiopathic is my all time least favorite word. My son had a catastrophic acute idiopathic lung hemorrhage that migrated into a chronic idiopathic lung bleed lasting over two years.
We still have no idea why.
The good thing is CRC is an extremely slow-growing cancer. So now that you are (i assume) going to be regularly screened, there is virtually 0% chance you will develop CRC advanced enough to cause harm. The worst you should have to endure is the same as your dad-polyps are found and excised during colonoscopy and sent to the path lab. They take it all out. CRC is almost completely preventable because of this. People who die from it are those who have it and don’t know because they’ve never been screened (young, afraid, whatever the reason). So your idiopathic scare, annoying as it is to not know the cause, actually may have saved your life anyway. ☺