Q: I have a five-year-old Japanese maple. It has never grown taller, only wider at the base. It resembles a mushroom with lacy leaves. We had some advice to prune the top out to promote vertical growth. As you can see it didn’t work. We would like to save it but have it look more attractive.
A: It looks to me like you have a perfectly normal-looking dwarf laceleaf Japanese maple.
Japanese maples come in all sorts of sizes. They can be 30 feet tall or 2 feet tall, depending on variety. Dwarf Japanese maples are either a variety that is naturally small or it has been grafted onto a rootstock that makes it grow small. Yours is most likely the grafted kind.
I am not sure why you want it to grow tall anyway. It looks to me like it would block your window.
I say leave it alone and enjoy it as it is.