Should I hire a lawyer to investigate possible medical negligence?

A CT scan performed this year showed a lesion/tumor on Mom's pituitary gland. The same lesion/tumor can be seen on CT scans performed last year, but none of her neuro doctors reported it. (She has to have multiple CT scans to check her VP Shunt. Ongoing since 2008).

Today we found out that her vision may not be repairable, even once the now HUGE tumor is removed by surgery.

I'm upset with the doctors. Should I should expect that the doctors would have said something last year, or 2009? Looking at the CT scans from last year, its crystal clear there's a tumor... but nothing ever was said.

Should I hire a lawyer to investigate? At the least there should be some censure for not doing a thing for my Mom when the evidence is staring at them in the face. Every visit we went to, I outline her symptoms and I report she's not getting better.

I feel like I'm constantly having to push doctors to help my Mom and I'm sick of it. What ever happened to "Do no harm"?

Why do most doctors not fully treat a patient. If you are a neurologist or a neurosurgeon and you see a problem (may not be your expertise, but the tumor is CLEARLY seen), shouldn't you report said tumor to someone? Shouldn't something be mentioned? Noted? Discussed?