Myself Dr Josh- A Board Certified Physician and I’m happy to help with your question today.
Well, Such pea size lump in his armpit could be- Epidermoid Cyst.
They grow slowly and don't usually cause any problems. He may want to remove it if it doesn't look good, or if it's painful, infected or ruptured.
Such cyst are round lumps and can be felt just beneath the skin surface. They are very common. Usually they are small of the pea size but sometimes they slowly get bigger over many months to become a few centimeters in diameter. No need to worry for that.
Regarding bony growth on skull could be related with collection of fibrous tissue with core bony material attached to his skull. One more possibility is sebaceous or epidermal cyst.
To be honest, I would not be worried for any serious issue.
This can be left alone.
For peace of mind, you can get a clinical examination done by doctor.
Hope this helped
If you have any further question then you can ask me.
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