Experts from a US museum believe it could be one of the oldest examples of advanced surgery. The Museum of Osteology in Oklahoma said the skull is reported to have been that of a man who was injured in battle before undergoing surgery to implant a piece of metal in his head to repair a fracture.
They discounted the idea because
This rarely happens when they pour molten metal on the head, according to medical experts.
(source: Snopes)
Couldn’t they have cast it and put the patch in after it cooled?
Thanks for the link, it also answered my question about the shape of the skull.
Thanks! I wasn’t seriously considering that it may have happened, just reminded me of movies (as I mentioned) and was keen to read more as no source was linked.