Radionuclide imaging of the thyroid gland: patterns, pearls, and pitfalls

Optimal thyroid scintigraphy requires an understanding of 1) the embryology, anatomy, and physiology of the thyroid gland; and 2) the properties of the 2 common imaging agents, technetium-99m pertechnetate (Tc-99m) and radioiodine (1-123). The normal gland has a characteristic scintigraphic pattern with these tracers and its uptake can be quantified with 1-123. Thyroid diseases often produce characteristic abnormal patterns. These abnormal patterns could be described as diffuse or focal, homogeneous or heterogeneous, increased or decreased. "Extrathyroidal" localization can be seen with esophageal activity, ectopic tissue, thyroglossal duct cyst, and substernal goiter. Thyroid scintigraphy of neonates, as a follow up to abnormal blood screening, demonstrates typical etiologic patterns. The first step in evaluating a patient with suspected thyroid disease is correlating the normal or abnormal scintigraphic pattern with available biochemical data, clinical history, and physical examination. By integrating the interpretive and technical "pearls" and "pitfalls" outlined in this article, the radiologist can be more confident in establishing a proper diagnosis.