??? EEG Results

My 10 yr old daughter had a strange episode in May which caused her to see a neurologist.  He did an EEG which he said showed some fluctuations when the strobe light was introduced so he ordered a 48 hour EEG.  He called me and said this one showed "some intermittent slow activity at the back of the head, this is not normal" and he wants an MRI done.  So, my question is... what could this possibly be?  Could it be a tumor?  

I would just like to know what possible diagnosis we could be looking at.

Thanks!