This January my then-15-month old son had a mild infection that made him throw up one time, gave him a slight fever for 2 or so days, and ruined his appetite. It also cause the gland behind his ears to swell to almond size lumps. (his glands have always been visible as he is naturally slim, but they're usually pea size). My doc thought it was a virus and said the glands were doing their job but were getting backed up. He waited a week or 2 and then when they were still big he gave him antibiotics. One side went down but the right side continued to swell until it was the size of a walnut, then a small chicken egg. We tried one more round of a.b.'s, then he got a CT scan (yuck) The specialist read them and said it was a cyst. By this time 5-6 wks had gone by and my ds was acting normal, except he was still picky with his food and didn't sleep as well (which didn't necessarily mean anything.) Dr. planned surgery for another month down the road to remove it.
When they opened it up, it turned out the lymph gland had gotten so infected that it abcessed (v. advanced) My son's strong little body had sealed off the infection and he'd gone about his business for 2 1/2 mos., never complaining of any pain, etc.
It was a frightening ordeal and I won't ever know what caused the infection or what could have happened if it'd been left to its own....Kids get glandular secondary infections from cat scratch fever, mono, even West Nile virus. But I think if the specialist had read the CT scan correctly, he might have been able to drain the abcess without surgery and treated the opened infection with antibiotics (which aren't for everything, but ultimately were necessary here).
BTW he's just fine now, and gained lots of weight and crazy toddler energy within a week of surgery. Kids have amazing powers to heal.