Melanoma brain tumor but no melanoma found anywhere else

My Father is 80 yrs old and in perfect health (routinely shoots low 80's golf rounds).  They found a brain tumor after his speech became slurred.  It was about 1.9cm in diameter, perfectly round.

PET, CT, bloodwork, MRI's, etc. all came back perfectly clear with the exception of the single tumor.

Was diagnosed as melanoma after a craniotomy this week.  The surgeon took out some of the tumor but backed off when he could not find a clear edge.  He didn't want to risk losing speech, etc.

Radio Oncologist and Oncologist are recommending stereotastic surgery.

Question-->  can melanoma start in the brain or is it always coming from somewhere else ?

We are checking his eyes for occular melanoma (remote chance).  He had cateracts removed and lens implants last year so we'd be surprised if they missed it then.   He had one Stage 0 melanoma removed from his cheek 2 years ago but no one feels that's the primary source.  Regardless, we're going back and re-doing head to toe skin evaluations for any missed melanomas (also feel this is a remote possibility).

Any ideas would be welcome.  Also could use any help understanding other treatment options.

[rumpled]

I actually was able to find a couple of cases using google. It is rare.

Since it is rare, I cannot comment on the treatment, but you dad is not the only one.