Abnormal Lymph Nodes on CT Scan of chest

My 25 year old son has had several episodes of upper abdominal pain, with the pain increasing with a deep breath. He saw a new doctor (thankfully) during the last episode, who scheduled a chest x-ray which showed "non-specific areas." Upon review of the radiology report, the doctor called my son (who was out of town at the time) and set up a ct scan of the chest. Within an hour after the ct scan the doctor called my son and said it showed "abnormal lymph nodes." The doctor now is recommending a lymph node biopsy. He hasn't seen the doctor since the first visit, it's all been through phone calls so he hasn't had the opportunity to sit down with the doctor and ask all the questions he has yet. It's all happening very fast. It is my understanding that an incision will be made in the neck area, so I am assuming that either partial or entire lymph node(s) will be removed instead of just a needle biopsy. Some of my questions are: What do abnormal lymph nodes on a chest ct scan indicate? What all will be looked for in the biopsy? Are biopsies of this type definitive? How accurate are the biopsies? All information and shared experiences will be helpful and appreciated. Thanks from a very worried mom.