In reply to dartfrog: I think you need to be a bit careful about just continuing climbing though it does depend whether the underlying damage has healed or not. It is difficult to tell.
I had a ganglion cyst on my ankle which caused no pain (although I knew the ankle was weak from another sporting injury) which grew from a small pea size when I first noticed it to almost the size of a golf ball. At this point I went to the doc who said that it's the damage to the sheath that surrounds the tendons causing the synovial fluid which lubricates the tendons to leak out. He used a syringe to extract some of the fluid (it's like a clear jelly substance) and said to return if the cyst increased in size again as this indicated the underlying damage had not healed.
Within a few weeks it had so I went back to the doc who said there was not point to keep lancing it and that I could either put up with it (as it caused no pain) and hope the underlying damage eventually healed and the synovial fluid would eventually dissipate & the cyst disappear or have an operation. Operations have a 100% success rate (according to him) if the damage was outside the joint but less if inside the joint.
As I'd had the problem for nearly 1.5 yrs I decided to have the operation and hope the enforced rest away from climbing would help heal the weak ankle I had which was probably causing the problem. I had an MRI scan which indicated it was inside the joint but I went ahead with the operation & was off climbing for 6 weeks. The op was a success and had no problems for about a year during which time I work an ankle support but then a small cyst returned (gutted) when I stopped using the support and so went back to using it and cyst eventually disappeared on it's own. That was 3 yrs over a year ago & I've had no problems since though continue to use the support off and on depending upon what climbing I'm doing.
Apologies if that's more detail than you wanted but I hope that helps. In summary the answer is it depends ! Depends upon whether it has or will eventually heal by itself or whether it causes pain or whether it's inside or outside the joint. What you musn't do though is whack it with a book !