Ladeeelisa,
I know it is hard, but try not too worry too much. The fact that the young man in not complaining of the mass bothering him is a very good sign.
Again, there are a whole host of benign soft tissues processes that this could be. A faint shadow on the x-ray is helpful, in that it rules out a bunch of bad things.
It does not seems to involve the bone, at least it is not a lytic (destructive) or blastic (bone forming). It does not seem to be a bone tumor.
A faint shadow on x-ray usually means that the soft tissue mass is solid. A cyst, such as a ganglion cyst, since it is fluid filled, what not show up on x-ray.
It could be a shotty lymph node. These are lymph nodes that have been swollen in the past, but the process that initially caused the node to enlarge, is no longer active. The node stays a little swollen, but is no longer tender.
There are a bunch of skin and subcutaneous masses, such as epidermal inclusion cysts and sebaceous cysts. These are very common around the head and neck region, but can occur anywhere on the body.
There is a benign fat tumor called a lipoma, that can occur anywhere on the body, and are very common.
So, again, try not to worry too much. The chances of this being something bad are very small. And, since it is not bothering your son, that is a great sign.
The physician will take a look at the mass. Most can be diagnosed based on the exam. But, if there is any concern, or if an exact diagnosis is needed, then the physician may order other tests, based on what she finds on the exam. These tests could include things such as an MRI, CT scan, bone scan, blood work, and in very rare cases, maybe even a biopsy.
Try not to worry and also, try not to upset your son. Let us know what the physician thinks this is, as other mothers may be in the same situation. Good luck.