I have been diagnosed with hypothyroidism and recently underwent a MRI and CT scan. A small mass was found and my doctor said it was probably from taking "lithium" and not to worry about it. No other tests or biopsy were done. I feel like there should be more examinations to determine if it really is caused by lithium. It has been 10 years since I took lithium. Has anyone who has taken lithium had this problem? Any information concerning a nodule or small mass in the thyroid area would be greatly appreciated.