Will a MRI brain scan be disrupted or worse if there are metal screws still in there?

Will a MRI brain scan be disrupted or worse if there are metal screws still in there?
I don't really understand your question. I think you are referring to the accuracy of an MRI if you have metal screws in your brain? I don't believe that would alter the accuracy as an MRI is very reliable in pinpointing problems. Ask your doctor for a guaranteed answer.
It's likely that you won't even be a candiate if you have screws still in your head. Most people with anyeurism clips and the like are contra-indicated for scans since it may lead to motion of the ojbect which could be bad.
If they indicate that you can do it, it may distort the images since the magnetic field will be altered due to the metal's susceptibility.
Most brain work is not done though since there is a concern for doing more damage than the scan will be worth.