This is a lethal mutation that appears in several species. I've seen it documented in humans, rabbits, rats, cats and dogs, so presumably it would appear in lions too.

It's caused by the gene that regulates the draining of brain fluid into the lymphatic system not functioning properly, and appears at birth or shortly after. Most animals that get it usually only live a few months at most.

It is characterised by a huge, domed head (which is the fluid that causes that). I have added two images that I've managed to find: one of a human with this mutation, and another of a young domestic kitten.

First, the kitten


Next, the human: