Garden Pests and Diseases: Sick Japanese Maple, 2 by Bails

Bails wrote:
Hi everybody,

We have a beautiful Japanese Maple in our yard that has recently started to look worse for wear. On inspection, I have noticed as though something is burrowing into the tree and am now panicking as I don't want to lose it.

I have attached a couple of photos of what I have discovered and am hoping someone can tell straight off what is causing the damage.

Thanks for your help in advance :)

Cheers,
Georgie