RADIOIODINE UPTAKE AND THYROID SCINTISCANNING
Section snippets
EMBRYOLOGY AND ANATOMY
A review of thyroid embryology is necessary to understand the many variations in location and configuration of benign functioning thyroid tissue that are encountered in thyroid scintiscanning. The thyroid gland develops from a thickening in the midline of the anterior pharyngeal floor, first noticeable about the sixteenth day of gestation. It expands as it descends ventrally while remaining attached to the pharyngeal floor by a stalk called the thyroglossal duct. This stalk begins to atrophy at
RADIONUCLIDES USED FOR THYROID SCANNING AND RADIOACTIVE IODINE UPTAKE
Only three radionuclides are used in routine clinical practice (Table 1). Of the two iodine radioisotopes, iodine-123 (123I) delivers far less radiation because of its short half-life (13 hours) and the absence of beta radiation. Its gamma photon energy of 159 keV is ideally suited for thyroid scanning. Previously, commercially available 123I had longer lived 124I and 125I contaminants. Reactor-produced123I is much purer, with virtually no 124I and less than 1%125I. Currently, 123I is available
MEASUREMENT OF RADIOIODINE UPTAKE
Radioactive iodine uptake was the first diagnostic nuclear medicine procedure. It was performed in 1940 in a primitive way using a Geiger counter. Contemporary methodology was introduced by Werner34 about a decade later. As in vitro thyroid function studies gradually became more sensitive, radioactive iodine uptake measurement was used less frequently as a measure of thyroid function. Its main role is in the evaluation of the hyperthyroid patient to distinguish subacute or silent thyroiditis
CLINICAL INTERPRETATION OF RADIOACTIVE IODINE UPTAKE
A variety of thyroid states are associated with abnormal radioactive iodine uptake measurements, and other factors can interfere with the value (Table 2). Causes of abnormal results include the following:
Increased uptake
Hyperthyroidism
Hashimoto's thyroiditis
Iodine deficiency
Subacute, silent, or postpartum thyroiditis in the recovery phase
Rebound after withdrawal of antithyroid drugs
Enzymatic defects in thyroid hormone biosynthesis
Choriocarcinoma and hydatidiform mole
Lithium
THYROID SCINTIGRAPHY
Thyroid scintigraphy or scintiscanning (hereafter referred to as scanning) permits visualization of the thyroid gland and functioning thyroid tissue elsewhere in the body. With the widespread use of fine-needle aspiration biopsy (FNAB) and ultrasound imaging, the role of thyroid scanning in initial evaluation of thyroid nodules has diminished. Nevertheless, there are clear indications for obtaining thyroid scans. The important role of 131I scanning in the postoperative evaluation of the patient
CLINICAL UTILITY OF THYROID SCANNING
Many thyroid conditions have been studied with scans. Current clinical uses of thyroid scanning include the following:
- 1
Demonstrating that a palpable enlargement represents an entire lobe rather than a nodule—hemiagenesis, asymmetric normal thyroid, firm Hashimoto's disease
- 2
Localizing functioning thyroid tissue—ectopic thyroid tissue, nonthyroid neck masses
- 3
Identifying the cause of congenital hypothyroidism
- 4
Identifying the cause of hyperthyroidism
- 5
Identifying functioning thyroid nodules
- 6
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2021, Revista Clinica EspanolaScintigraphy has the potential to replace thyroid stimulating hormone and ultrasonography in hyperthyroidism diagnosis
2020, Saudi Journal of Biological SciencesCitation Excerpt :A study demonstrated that more than 70% of patients with an AFTN referred to the hospital had normal TSH level (Chami et al., 2014). Main thyroid scintiscanning uses includes the diagnosis of hyperthyroidism cause and the identification of normal and ectopic thyroid tissue (Meier and Kaplan, 2001). In this study, thyroid scintigraphy was superior to US (90% vs. 84%) in identification of hyperthyroidism autecology.
Update on the role of ultrasound guided radiofrequency ablation for thyroid nodule treatment
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2016, FMC Formacion Medica Continuada en Atencion PrimariaAmerican association of Clinical Endocrinologists, American college of endocrinology, and Associazione Medici Endocrinologi medical guidelines for clinical practice for the diagnosis and management of thyroid nodules - 2016 update
2016, Endocrine PracticeCitation Excerpt :On the basis of the pattern of radionuclide uptake, nodules may be classified as hyperfunctioning (hot), hypo- functioning (cold), or indeterminate (139 [EL 4]). Hot nodules almost never represent as clinically significant malignant lesions, whereas cold or indeterminate nodules have a reported malignancy risk of 3% to 15% (244 [EL 3],245 [EL 4-review]). Because most thyroid lesions are cold or indeterminate and only some of them are malignant (246 [EL 3],247 [EL 3]), the predictive value of hypofunctioning or indeterminate nodules for the presence of malignancy is low.
Role of isotope scan, including positron emission tomography/computed tomography, in nodular goitre
2014, Best Practice and Research: Clinical Endocrinology and Metabolism
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