Toxic Adenoma other imaging findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

Overview

Radionuclide imaging and quantitative radioisotopic uptake studies are always required to establish the diagnosis of toxic adenoma or toxic nodular goiter.^[1]
Radionuclide imaging can be performed with radioactive iodine-123 ( 123 I) or with technetium-99m ( 99m Tc).^[2]
Radionuclide imaging performed with 123 I or 99m Tc-technetium pertechnetate, are trapped by the sodium-iodide symporter in functioning thyroid tissue, although only radioiodine is subsequently organified.
In patients with hyperthyroidism caused by a toxic adenoma, there is a characteristic restriction of radionuclide uptake to the responsible hyper functioning nodule with suppression of radionuclide uptake in the remainder of the gland.
In a patient with a low serum TSH concentration, not only does the scan appearance support the diagnosis of toxic adenoma, but in almost all cases it also excludes malignancy in the nodule.
If some thyroid nodules are hypo functioning, it is necessary to rule out cancer by fine-needle aspiration cytology.

Differential for thyrotoxicosis	Fractional Uptake of Radioactive Iodine in 24 hrs (%)	Radioactive iodine Distrubution
Graves’ disease	40-95	Diffuse (Homogeneous within thyroid)
Toxic adenoma	20-60	Restricted to autonomous regions in thyroid
Subacute thyroiditis	<2	minimal uptake
Silent thyroiditis	<2	minimal uptake
Iodine-induced thyrotoxicosis	<2	minimal uptake
Factitious or iatrogenic thyrotoxicosis	<2	minimal uptake
Struma ovarii	<2	Uptake in ovary
Follicular carcinoma	<2	Uptake in cancer metastasis
Thyroid-stimulating hormone–induced thyrotoxicosis	30-80	Diffuse (Homogeneous within thyroid)

↑ Hurley PJ, Maisey MN, Natarajan TK, Wagner HN (1972). "A computerized system for rapid evaluation of thyroid function". J. Clin. Endocrinol. Metab. 34 (2): 354–60. doi:10.1210/jcem-34-2-354. PMID 4110446.
↑ Smith JR, Oates E (2004). "Radionuclide imaging of the thyroid gland: patterns, pearls, and pitfalls". Clin Nucl Med. 29 (3): 181–93. PMID 15162989.