How can I best broach the subject of a misdiagnosis with out questioning a doctor's throughness?

Swbailey asked...

My step-mom has been diagnosed with dementia/Alzheimer's and though I may be clutching at straws I have read some information about Normal Pressure Hydrocephalus (NPH) and how it has symptoms similar to dementia/Alzheimer's. I have contacted her doctor and neurologist and though they did a CT scan there is no indication that she has had an MRI. How can I best broach this subject with her physician without questioning his thoroughness?

Contact with him has revealed the CT results but I am not sure how to proceed from here. The neurologist just asked my step-mom a few questions at one time and stated that she has dementia based on her answers.