Hi,
I'm not a doctor but I do work in science and I'm diabetic and had problems with my liver so I hope this helps. If your doctor has sent your son for a scan it's probably because some blood work came back unusual, this is generally the LFT's (liver function) It could be caused by lots of different things, but the liver is one of the most awesome organs and is very good at healing itself. At the scan they will be primarily looking at the size of his liver and if there are any obvious scarring of legions or anything unusual. With me I had NAFL (non alcoholic fatty liver disease) which was due to my very erractic blood sugar control over 3 or 4 years. This is probably the most likely cause it is with most people and it will heal itself providing that sugars are kept under control and probably if he either loses weight or if not over weight then adopting a more healthier diet. It could also be a fatty liver from drinking too much, which will again heal itself if alcohol is reduced and a healthy lifestyle adopted. Or it could just show that the liver is normal on the scan and your son may have a virus or infection that has made is bloods temporalily abnormal. If he does have an enlarged liver the next stage is generally a biopsy. This sounds really scarry but it's not infact when I had mine done it was just a local anasthetic and in and out on the same day I even managed to get a good look at the sample he had just pulled out of me. the sample is then analysed in a lab and the consultant will advise then the best course but usually with livers it means healthy lifestyle and cutting down on the booze.
Hope that helps, Laura