Once in a while, you will read a report about somebody having a medical examination and then having something removed from their body that was foreign to the body and yet was present there for years and years. It seems most unlikely, after all, how can something be present in the body for so many years and not come out, or not even be able to feel that foreign object in the body and so on. And yet there are cases where a person has got a bullet in their body for years and even decades and it was fine, until one day when it started causing problems and has to be removed. In this case, a person had a needle in their ass and after decades, the needle finally started causing problems and had to be removed (link to article):
Kiran Kumar, from Malayankeezhu in Kerala's Thiruvananthapuram, has been living with a sewing needle in his rear for the last 22 years. Kiran, now 34 years old, had gotten the needle pierced inside when he was in the sixth grade after he sat on it. It seems he was taken to a hospital then, but the doctors weren't able to find the needle. Nor did he undergo any further check up because there was no pain or discomfort. But two weeks ago, after 22 long years, Kiran felt immense pain in his rear and went to a private hospital for check up from where he was referred to Thiruvananthapuram medical college hospital. Doctors there found that the needle is the cause of pain and swelling and understood it was one and half inches deep inside his body. They couldn't find the exact location then.