Was it a shipped chick? Did you have them vaccinated? I've seen something KIND OF like that, when I was giving my hens IV antibiotics.. Apparently I missed, and the hen that had the shot got a large fluid filled area on her neck like that
She recovered, but that's the only thing that I can think of.
It could very well be the same thing then. I know when I gave the shot to mine, she was ok, but the next day there was a fluid filled area about the size of a .50 cent piece.