Toxic Adenoma other imaging findings: Difference between revisions

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*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.
*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 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 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.  
*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.  
*It is important to remember that there is a differential diagnosis for this scan appearance, including congenital hemiagenesis of the thyroid with compensatory hypertrophy of the sole lobe, previous hemithyroidectomy, asymmetrical subacute or autoimmune thyroiditis, or a large hypofunctioning nodule in the contralateral lobe. However, in none of these conditions would a low serum TSH concentration and elevated thyroid hormone levels be expected unless the patient coincidentally had another condition causing thyrotoxicosis. In patients with toxic multinodular goiter, the radionuclide scan shows more than one focal area of increased tracer concentration with suppression of extranodular thyroid tissue (see Fig. 14-2 ). If some thyroid nodules are hypofunctioning (cold), it may be necessary to rule out cancer in them by fine-needle aspiration cytology before defining the optimal plan for treatment of the patient’s hyperthyroidism (see later).
*If some thyroid nodules are hypo functioning, it is necessary to rule out cancer by fine-needle aspiration cytology.
{| class="wikitable"
!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)
|}

Revision as of 18:00, 7 September 2017

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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
  • Radionuclide imaging can be performed with radioactive iodine-123 ( 123 I) or with technetium-99m ( 99m Tc).
  • 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)

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