Once a lump in the thyroid is discovered, it is important to know whether it is benign or malignant (cancerous).Often an ultrasound is performed to assess whether there is a single nodule or whether multiple nodules are present. Ultrasound can determine whether the nodule is fluid filled or solid. Ultrasound also can determine the general appearance of thyroid looking for inflammation or irregularities and the presence of enlarged lymph nodes nearby that may represent metastatic cancer.Fine needle aspiration biopsy is the procedure performed to obtain a sample of cells from the nodule to determine if it is cancerous. Using ultrasound, a thin needle is placed into the nodule and cells from the nodule are obtained. These cells can be examined under a microscope by a pathologist to determine whether a cancer is present and if so, what type of cancer it is.Results of the aspiration are usually reported as the following:
Malignant: risk of malignancy is 100%
Suspicious for malignancy: risk of malignancy is 50% to 75%
Follicular carcinoma: risk of malignancy is 20% to 30%
Atypical cells of unknown significance: risk of malignancy is 5%-10%
Benign: risk of malignancy is less than 1%
Sometimes, the results of the aspiration are unclear and indeterminate, and the aspiration may need to be repeated to get a better sample and more cells to study.Another test involves ingesting radioactive iodine, which is taken up by the thyroid gland. The gland is scanned by a Geiger counter-type of apparatus that determines how much radioactive iodine has been taken up by the gland and any thyroid nodules. If the nodule picks up much of the iodine, it is referred to as a "hot nodule." Such nodules are rarely cancerous. Nodules that take up little to no iodine are referred to as "cold nodules." Although the overwhelming majority of such nodules are benign, 5% turn out to be malignant. Although thyroid scans may be helpful, aspiration of the gland is a much more useful test.Blood tests may be ordered to determine thyroid hormone levels and levels of other hormones and electrolytes, like calcium, within the body. These tests indicate whether the cells of the thyroid produce too much or too little hormone, not if cancer is present.On occasion CT, MRI, or PET scans may be useful in evaluating the neck structures if there is concern that thyroid cancer has spread (metastasis).