I have been having migraines so went for an MRI. The results say I have a 2.5mm aneurysm at the junction of the right A1/2 segment, directed posteromedially. Can you please tell me exactly what this means? Where in my brain is this? How long are A1 and A2 segments? I have to see a Neurologist, but have been googling to try and find out what this means as I can't concentrate on anything else at the moment.