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

Other Imaging Findings

  • 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)

References

  1. 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.
  2. Smith JR, Oates E (2004). "Radionuclide imaging of the thyroid gland: patterns, pearls, and pitfalls". Clin Nucl Med. 29 (3): 181–93. PMID 15162989.