A mass in his neck??

Connor's school nurse called me. His teacher noticed a mass in his neck, and called the nurse, then the nurse called me. I actually thought I saw something yesterday, but it was when we were eating and he was sitting across from me. I made a mental note to check it later, then forgot.

Anyway, he has a large mass on the left side of his neck, a little off of midline. It looks like one large mass vs several small ones (he has chronically swollen glands, but those are further back and are multiple small knots, nothing like this).

The nurse said I don't have to pick him up, he has no fever, no rash, he's acting normal, he's been eating normal, sleeping normal...

We all were sick last week, and my husband and my oldest son had strep throat. But Connor and I had only colds, and we got over them no problem. No one has any signs of illness anymore. And even when Connor was sick, his fever was never high, his glands weren't swollen then (any more than normal anyway) it was mostly sinus and a bad cough (he used his inhaler a lot, had a few bronchospasms, etc)

So what the heck is this??? He has a pulmonology appt tomorrow afternoon, so we're going to have his pulmo check it out (I called the nurse already and asked if the dr would look at it, and she said absolutely)