Anxiety over sons health

I’m in a full blown panic! When my son was a year old, we found some big lymph nodes on his neck. Doctors did all the testing, and chalked it up to just a fatty benign tumor. Now, 8 years later, he had a case of intussusception. His doctor is wanting to do blood work, and an MRI. Of course, my anxiety brain is freaking out thinking my kiddo has cancer, or some life threatening illness. He is a healthy, athletic happy 9 year old. What would cause his lymph nodes to be on the bigger side in his abdomen?!