I'm so sorry for your loss and I'm sorry that they have let you go home distressed and not understanding your baby's condition. They should have given you time to process the shock and then explained it and answered any questions you had.
I can give you a bit of information if that helps as I took a special interest in neural tube defects so researched it a lot but I'm not a doctor so my understanding is limited and you should definitely take your advice from qualified medical personnel.
From experience (not mine but family) you will see the specialist to confirm the diagnosis. This usually happens within a couple of weeks. You may be sent for a fetal MRI to get a better look at the structure of your baby's brain and the contents of the balloon shaped sac you saw.
They will confirm the diagnosis or it may be found inconclusive or incorrect. You will be given the options depending on the results to either terminate or attempt to carry to term.
If it is anencephaly and you do not terminate, it is quite likely that you will miscarry. Termination on that case is the best option for all 3 of you.
If the results are inconclusive then it is a personal decision and I encourage you to do your research and make the decision you feel most at peace with.
It won't be treated as an emergency as the baby either has it or doesn't and there is no treatment to give. Personally I hate this as I think it is beyond cruel to force a mother to wait in limbo to find out if her child will survive. I'm so sorry you are in that position.
If you don't want to know details of the condition itself just stop reading here, I have no desire to distress you further with 'maybes' and 'sometimes'.
Unfortunately there is nothing anyone can do to treat anencephaly. Its a failure of the neural tube to close and means parts of the brain and skull have not developed or are missing entirely. I'd hazard a guess at skull being open as I've never seen it look like a balloon before so possibly the brain growing outside the skull. Normally you see that with hydrocephalus rather than anencephaly but every case is different.
It's quite rare. I think the oldest child with this condition lived to be 5 years old. He didn't have much function though and there was debate at the time over how aware he was. I believe it depends on how much and what parts of the brain are missing.
In your babies case, if they've offered you a termination, it's likely enough is missing that he or she would not be able to support their own life functions. Currently the placenta provides oxygen and keeps them alive. Once born, they would not be able to support their own functions. No reflexes mean unable to breathe, swallow, blink or protect their own airway. The nervous system may or may not have developed and its possible that cardiac activity will stop shortly after birth.
I really hope this has helped you understand a little more and not made you feel worse. I'll be thinking of you and your little one. I know my cousins partner used a support group on a forum, I'll ask her what it was. Her baby didn't have anencephaly but her pregnancy was aborted due to a condition that was similarly incompatible with life.