Is there any precedence of a brain tumor causing insanity?

Did you smash it

so that the sufferer can’t tell the difference between right and wrong?

There was a case in USA of a mass shooter some decades ago, before availability of scans, and an autopsy revealed a tumour in an area of the brain dealing with compulsive behaviour iirc.

edit - an article about the case:

https://www.scientificamerican.com/article/how-responsible-are-killers-with-brain-damage/

There are a lot of medical articles which detail how brain tumours can affect behaviour. It happened in my own family that secondary tumours on the brain definitely altered ability to be responsible for oneself.

https://www.moffitt.org/cancers/brain-tumor/symptoms/mood-changes/

Another science article about brain lesions & criminal behaviour

https://www.sciencedaily.com/releases/2017/12/171218154935.htm

So it would appear very much a brain lesion can cause profound changes in personality and serious behavioural changes, but I think most people suffering brain tumours do not have such far reaching personality changes.