Why are the reasons for biopsy of cold spot thyroid scan results?

Answer 1

Thyroid cold spots are areas of decreased radionuclidic uptake, meaning that particular area of the thyroid is not metabolizing iodine. These finding are consistent with cysts, hypothyroidism, benign growths, inflammation, or malignancy. In addition to a scan, an uptake is often performed. This is done by counting the activity of the radioactive iodine (RAI) with a gamma probe, administering the RAI (commonly in pill form), and then positioning the patient about 8cm from the probe and counting activity over the thyroid commonly at 6 and 24 hours post RAI administration. This is helpful in determining if the thyroid is hypo, hyper, or normal (euthyroid). Uptake percentages relative to the initial activity are considered normal within the ranges of 10-30% respectively. Thyroid inflammtion can mimic the uptake values of hypothyroidism. In addition, the patient should not have any study using RAI if they have a study requiring the use of Iodine contrast (eg contrast enhanced CT), take multivitamins containing iodine, have recently taken cold medicine containing iodine or antihistimines including diet pills, or if they are on a special diet containing kelp or seeweed tablets. In patients with known hypothyroidism, thyroid suppressive medication (eg Synthyroid) should be discontinued for 2-6wks prior to RAI administration. Back to the scan... A single cold spot is malignant in about 10-20% of cases. Therefore, a biopsy is helpful for providing a differential diagnosis using laboratory histology.