Help pls - Acer not leafing out?

Hello, We are in Yorkshire, UK, and have what I think is a Japanese Acer in our garden, we have had it for many years and noticed that this year it only has leaves on the bottom, not the top. Can anyone let me know why this is? Please see the photos. Thanks, Simon (#notagardener)

 

Give the top parts the scratch test, just scrape the bark and see if its green underneath, if it brown then that part is dead.
I think you might have some dieback there.

Dont do it yet but later in summer you can cut back any dead stuff to the parts that are still alive.