Hi...
Children bones are very soft hence remodeling is very good. Gradually the indentation will subside.
since he has no major signs of
head injury and its already 4 months post , very unlikely he will have any major
brain injury.
The more concerning part is the painful bulge.
Usually the painful bulge in the scalp is due to soft tissue injury/ infection.
In your scenario its 4 months post looks more like a
soft tissue infection.
Scalp infection is a major infection as it can spread fast.
It is advisable to take him to the hospital to conform the diagnosis and treat accordingly.
Things to do as of now-
1) if any wound visible then keep in wound clean and dry.
2) see for signs of infection-
redness, swelling, pain, local rise in temperature/ warmth on touching, tender
3)if present then he has to be started on antibiotics (depending on the weight the dose has to be adjusted).
3) can continue
tylenol.
It is advisable to take him to the hospital to conform the diagnosis and treat accordingly.