mysterios bumps

[Dannyp2]

My two year old son has three small boney type bumps on the left side on the back of his head what are they?
First let me explain that my son was diagnosed with hydrocephalus or commonly known as water on the brain. He was 7 Weeks premature due to the fact that the umbilical cord was strangling him. It was determined at three months old he had hydrocephalus by our pediatrician we were sent to see a neurologist he said he did have a lot of excess fluid in his head but did not have hydrocephalus as the soft spot was not swelled, but his head did exceed the normal size and this had him very concerned. He has been to see the neurologist many times now and every time his head is above normal.He has no learning disabilities to our knowledge but about one year ago we noticed four or five small bumps on the left back side of his head. We told our pediatrician about them who thought it must be some kind of skull fracture. So he had some x-rays made and told us not to worry nothing showed up. We still were concerned so we pointed them out to the neurologist who took more x-rays he said the same thing as the pediatrician nothing shows up I don't know what this is but we should not worry about it. Well that was 8 months ago and now instead of four or five pea sized bumps there are now three marble sized bumps which have me concerned. Two of the bumps seem to be combining into two other bumps making them larger. I told the neurologist about this at our last visit but all he did was feel them agree that they were larger tell us not to worry again as the x-rays had ruled out skull fractures, aneurysms, tumors, and calcium deposits, but we still have no explanation of what it is. I am not trying to make a problem but I do expect an answer they have only done a cat-scan but they have not tried a biopsy or an M.R.I. We now are getting a second opinion but I still feel it necessary to do my own investigation. If any one knows what this could be please let me know. Sincerely A Concerned Father