I wanted to know if anyone else received completely different opinions from NS. I was diagnosed with a 5mm chiari in 2008 and told "it was mild and shouldn't cause probs" by two neurologists, and it really never did. I don't have headaches or other classis chiari symptoms and my quality of life is fine. Recently I had some arm weakness, so I went to a neurologist where I live now who ordered an MRI. She called me a few days later, in a panic, and said that my chiari had caused a syrinx and that I had to get in with a NS as soon as possible, she was even nervous about waiting over the weekend. So when I talked to the NS, he was very firm that I needed decompression surgery and that I had blocked flow, etc... He said "if I thought you had been walking around with this syrinx for years, my opinion might be different, but you have a syrinx and I have to recommend surgery". So that started what would become the scariest, most horrible, anxiety ridden weeks of my life. Im sure MANY in this group can understand that feeling of having to do something you desperately don't want to do. I probably had anxiety attacks every day and kept thinking I was going to become paralyzed at any moment, was afraid of every little feeling I had in my body, and thought of nothing else 24 hours a day other then surgery fears. I wanted to get a second opinion, just to be SURE that surgery was hat I needed, so I sought out a chiari specialist NS, and went to Johns Hopkins in Baltimore on Tuesday... His opinion was 100% opposite. He said he didn't even see a syrinx on my MRI, and that the spot was something completely different AND that my chiari was mild and my flow wasn't blocked enough that he would recommend surgery at all. He even said he doesn't see the need for me to ever have another MRI scan and also that at my age of 40 its very unlikely that the chiari will start to give me problems. I was in SHOCK and ofcourse I have never been so relieved and happy in all of my life. I felt like he gave me back control of my life. I still cant even believe he said that because I was so wrapped up in dread for weeks... I ofcourse feel worried now that the first NS was right (though he was not a specialist but he has experience with chiari), I wonder if anyone else ever had such drastic differing opionions and did you go for a third? As you can imagine, if the third agreed with the first, I would be devastated....
Sibby, what is the “spot” in your spinal cord? How big is it? Get a copy of the radiologists report -there’s a third opinion right there. You should get a copy from the first mri too. I can see why you are relieved, but not at peace with it. I would keep getting opinions till I felt like I knew what my imaging really showed.
Jenn 
If you had 2 very differing opinions in anything else in your life, would you just decide the one you liked best was correct?
Or would you decide that 1 was wrong and 1 was right but, unsure which was which, try to get further clarification?
You describe arm weakness in your note. Do you still have symptoms? If no, waiting may be appropriate(but I completely agree with Rebecca concerning a repeat MRI and Jenn concerning getting your own copy of the reading). If there was a change from the MRI from 2008, and you have new symptoms, at a minimum I would suggest you want to monitor for any future anatomical(MRI) or clinical(exam) changes. Did anyone directly compare the 2008 MRI to the 2015 MRI? If not, that would be another reasonable route(but the onus would be on you to get the original images and ask the current radiologist to supply an addendum to your MRI report).
Waiting may be very reasonable. I'm not sure I'd be comfortable completely ignoring new symptoms and new MRI findings.
I would definitely get a third opinion just to break the tie. Having seen many patients like you describe yourself, a middle ground may make everyone feel better(following with your neurologist for any clinical changes, and getting a repeat MRI in the future to confirm stability).
It may simply be that you have a visible central canal that was seen on a better MRI(perhaps the original MRI was 1.5T and the new MRI is 3T, giving a better picture).
Thanks to all 3 of you for your comments/feedback.. Honestly, the first MRI was just of the brain, 2008, when chiari was diagnosed. The 2015 was neck but showed the chiari. 2008, both neurologists said "mild, nothing to worry about" the 2nd opinion NS 2015, said the same. I honestly don't remember exactly what the final NS said the spot was on the MRI (that the other NS said was syrinx), because I was in such SHOCK that he said it wasn't a syrinx. I made sure my husband was absorbing and listening. He said it was something common and not something to worry about. I do still have some arm weakness, BUT my MRI also showed some degenerative disc in my neck, which can also cause arm weakness. My chiari, since diagnosis, has stayed the same (as far as symptoms) and hasn't caused any big problems... Or even bothersome ones at all.. I think I will get a third opinion from another experienced specialist, soon. And just hope he/she has the same opinion as the last! : )