Case 14 cont'd
Image findings: - Scan shows increased diffuse and uniform radiotracer uptake in the thyroid gland.
A. Toxic multinodular goiters on thyroid scintigraphy classically have a non-homogenous uptake of radiotracer. The thyroid appears as having different areas of hot and cold nodules of varying sizes.
B. De Quervain’s disease (aka subacute thyroiditis aka granulomatous thyroiditis) is associated with destruction of thyroid gland tissue by inflammatory infiltration. Although the etiology is unknown, viral infections are speculated to be the cause of this inflammatory process. Patients may present with history of recent viral infection and tenderness in the neck region. As thyroid cells are destroyed, imaging with Tc-99m pertechnetate shows lack of radiotracer uptake in the affected region/lobe. As it may present with transient hyperthyroidism, it may be mis-diagnosed as Grave’s disease. Subacute thyroiditis should always be considered before treating patients for thyrotoxicosis with radioiodine.
C. A thyroid follicular adenoma is a benign finding on thyroid scintigraphy. In most cases, these adenomas will show up as cold nodules (area of decreased activity) on thyroid scintigraphy (an estimated 95% of cold nodules are benign). However, an adenoma may also show up as a hot nodule (almost all hot nodules are benign and very rarely a sign of cancer). This would be a rare finding and a patient presenting with a hot adenoma (i.e., increased radiotracer uptake and increased activity) may also present with hyperthyroidism.
D. Graves’ disease is an autoimmune disorder caused by the production of thyroid-stimulating immunoglobulins. Patients present with hyperthyroidism and may present with enlarged thyroid gland (goiter). On thyroid scintigraphy, Graves’ disease typically presents as diffuse, uniform and symmetrical increase of radiotracer uptake in the thyroid lobes.
Q1. Answer: D.
Discussion:
The figure below (see Figure 1) highlights typical findings in thyroid scintigraphy and their most likely diagnosis. The indications of thyroid scintigraphy are indicated below:
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Investigation to evaluate findings during physical examination (such as a palpable nodule)
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Detection of metastases in patients diagnosed with thyroid carcinoma
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Follow-up of radioiodine therapy for differentiated thyroid cancer
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Determination of function of thyroid nodules
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Establishing a differential diagnosis for mediastinal masses
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Screening after head and neck radiation.
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Detection of extrathyroidal tissue (lingual thyroid)
Although Graves’ disease is not an indication for thyroid scintigraphy, a thyroid scan may still be performed to evaluate size of the gland to adjust dosage of Iodine-131 therapy and to evaluate diffuse versus nodular uptake in hyperthyroid subjects.
Aside from the use of Tc-99m pertechnetate for thyroid imaging, iodine-123 may also be used. In those cases, iodine-123 is administered to the patient orally, in the form of a capsule (dose of 100-400 mCi) and images are obtained at 6 and 24 hours. As with Tc-99m pertechnetate imaging, the patient is positioned supine, with the neck extended and the chin up. Anterior, 45° left anterior and right anterior oblique views are acquired. Palpable nodules and masses and scars are noted, and relevant landmarks are indicated (chin and suprasternal notch).
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Figure 1 – Possible scintigraphy findings on thyroid scans and their related diagnoses