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 (I-123). The normal gland has a characteristic scintigraphic pattern with these tracers and its uptake can be quantified with I-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.
Thyroid scintigraphy remains an important tool for guiding clinical and surgical decisions. The most common indications for diagnostic imaging are: 1) the evaluation of the nodular or enlarged thyroid gland, thyrotoxicosis, and neonatal hypothyroidism; and 2) the characterization of ectopic tissue or mediastinal masses.
This article first reviews thyroid embryology, anatomy, and physiology. Second, it compares and contrasts I-123 and Tc-99m as imaging agents. The majority of the article discusses and illustrates characteristic scintigraphic patterns of benign and malignant thyroid diseases (Table 1). These serve as a framework to share helpful interpretative and technical pearls and pitfalls for the practicing radiologist.