I don't think the drs. would keep information from you--from what I've experienced with neuros, they throw out all the possibilities (terrifying or not), and then you're stuck going "WHAT? TELL ME WHAT IT REALLY IS, NOT THE %&*$*# SCARY THING IT *MIGHT* BE!!!!!"
My sons have a lot of white spots on their MRIs, and they have a condition called Tuberous Sclerosis. The "tubers" are non-cancerous areas of the brain that harden and calcify (thus the white spots), and they're what cause the seizures my boys have. TS is about 1/6,000 births, and it's a non-inherited condition most of the time. It's also a disease that is very different person to person...there are people with TS that are totally typical, and there are kids with TS like my boys--very severely affected. Most kids, from what I've read, are pretty close to "normal," but with a higher chance of learning difficulties, epilepsy, and being on the autism spectrum. A lot of it has to do with how many "spots" (and therefore disruption) are in the brain...my sons have dozens and dozens, some large and some very small (the two worst ones were removed for seizure control...one was the size of an egg, the other a little larger). Most people that have TS and are pretty typically-developing kids only have a few spots. Location also matters.
All this being said, it's just one of the reasons a child might have white spots in an MRI. Don't let yourself diagnose with Dr. Google.
If you're really worried, call those doctors back and ask them to list out what the white spots might be, and whether they feel they (or you) should be finding out EXACTLY what they are, and when.