Ultrasound scan showing a nodule in the left thyroid lobe of a 28 year old female patient. The nodule measures 51 mm across on its long axis and 31mm on the anteriorposterior axis. Thyroid nodules are solid or fluid-filled lumps that form in the thyroid, a small gland located at the base of the neck. Most thyroid nodules aren't serious and cause symptoms. A small percentage of thyroid nodules can be cancerous.