My son 39 yrs old has a swelling on the left side of his adams apple. it is soft and feels like a fatty tumor. thyroid tests came be in normal range.

DDx: There is a differential diagnosis (ddx) including fatty tumor (lipoma), thyroid adenoma (non-functioning = normal thyroid studies), thymoma, lymphoma, etc etc. Follow up with md and consider further testing if it is growing, painful, etc.

Sounds like: He needs imaging studies to find out for sure. Consult a head & neck surgeon who can evaluate and order proper tests.