Unless someone put it in their brain, there’s not a way for a “fetus” to exist up there - but you CAN have a few different species of parasites in your brain!
The most common one to cause serious (sometimes lethal) complications is called cysticercosis, and is caused by the introduction of pork tapeworm (Taenia solium) to the bloodstream. This is very rare, but occasionally occurs when someone ingests the tapeworm eggs and they get absorbed into the body, instead of into the intestine (where they want to be). If they cross the blood-brain barrier, they have nothing to eat, and nowhere to go, so they go into this “stasis” mode, where they create hard little cysts wherever they end up.
Read more on neurocysticercosis at Discover - Carl Zimmer has a great article about how it might be more common than we previously thought…
Edit: Yes, technically a teratoma CAN exist in a brain, but there are no instances of fetus in fetu occurring in there, so I don’t count that as a “real” fetus - teratomas are not fetal tissue; they are congenital tumors, even though they may develop hair and teeth and sebum and skin.
Cool! If her skull keeps thickening, maybe she can win a harem of wildebeest or antelope! I wouldn’t advise going against the bighorn sheep, though; those guys have a honeycombed “double skull” in addition to the thickened bones.
By the by, for anyone who doesn’t know, hyperostosis frontalis is exactly what it sounds like - “hyper”: excessive, over - “osto”: bone - “-sis”: process, condition. And “frontalis" simply refers to the "frontal crest" - the flat-ish, "forehead" region of the frontal bone in the skull.
Put it together and you can see that the term means, roughly, “a process producing an excessive frontal bone”. The condition is pretty common in post-menopausal women, and as the thickening is internal, it is not usually discovered until a CT or MRI is taken for some other condition. The cause of the thickening of the bones isn’t known, but given that the majority of the people who have it are post-menopausal women, it’s assumed to be hormonal.
~ Interestingly, hyperostosis frontalis used to be thought to actually be a clinically significant finding, back before CT/MRI scans made it possible to see the skull prior to death. As the finding wasn’t universal, but not uncommon, in older women, pathologists thought that it went along with numerous other fatal conditions, and at times, actually used it as a “shortcut” to finding the true cause of death. Unfortunately, none of those assumptions turned out to be correct - the bone thickening on its own has no significant clinical implications (other than there may be a potential hormone imbalance in a younger person - but even this doesn’t have a high correlation).
I looked back, and you haven’t asked this yet, if it’s any consolation to my long response time! ><
She may well have seen the skull. As the dermis + epidermis can be less than 0.5-1 mm thick along the skull, and as children tend to have very thin subcutaneous fat layers on the forehead, it’s easy for a bat to break through all of the layers that are present. My own brother had the skin on his lower jaw busted straight through around the same age - while it required a few stitches, at least the bones are more resilient than the skin!
I don’t even…what are you talking about? The whole brain? None of it? The brain stem? the cerebrum? I really would…actually, I’m not sure if I want clarification on what you’re asking.
There are a lot of structures in the brain, but unless you’re into squishiness, I don’t think any of them would make particularly good sex toys. Just sayin’?