The head threads onto the rest of the pump. It looks like the threaded piece has pulled out of pump body. At best, you'll need to get a new pump body. Yellow Jersey sells them for $40: http://www.yellowjersey.org/silca.html

You'll still have to get the head off- but it should just unthread from the stub of the pump body.

Do you have to have a Silca Impero? I used to be a diehard Silca fan until I found the Topeak Road Morph pumps. Now I won't have anything but a Road Morph.