Thyroid Imaging Selection Guidelines

Diagnostic Algorithm for Thyroid Imaging

• The American College of Radiology recommends starting with thyroid function tests, particularly TSH, before any imaging, as the TSH result will guide the appropriate imaging pathway 1, 2
• For patients with normal TSH (euthyroid state), thyroid ultrasound is the preferred first-line imaging modality, as it provides superior morphological evaluation 1, 2
• For patients with low TSH (thyrotoxicosis), thyroid ultrasound should be performed first to evaluate thyroid morphology and nodules, followed by a radioiodine uptake scan to determine the cause of thyrotoxicosis 2, 3, 4
• For patients with high TSH (hypothyroidism), imaging is generally not indicated, but if needed, ultrasound is the appropriate first choice 4
• The American College of Radiology suggests that radionuclide uptake scan may have a role in evaluating goiter only if it is associated with thyrotoxicosis 2, 3
• For thyroid nodules, ultrasound provides high-resolution imaging to characterize nodules for malignancy risk, and radionuclide scanning is only indicated for nodules when TSH is suppressed 1

Benefits of Ultrasound as First-Line Imaging

• No relevant facts with citations.

When to Proceed to Thyroid Uptake Scan

• A thyroid uptake scan should only be performed when TSH is low (suppressed) 1
• The scan can help differentiate between causes of thyrotoxicosis, such as Graves' disease, toxic adenoma, toxic multinodular goiter, and thyroiditis 2
• It can also be used for planning radioactive iodine therapy 2
• Additionally, the scan can confirm that an entire goiter consists of thyroid tissue 2

Common Pitfalls to Avoid

• Proceeding directly to uptake scan in euthyroid patients is not recommended, as it wastes resources and has low diagnostic value 1
• Using radionuclide scanning to determine malignancy in euthyroid patients with nodules is also not recommended 1, 2
• Failing to check TSH levels before selecting an imaging modality can lead to unnecessary testing and radiation exposure 1, 2

Indications for Thyroid Scintigraphy

Main Indications for Thyroid Scintigraphy

• The American College of Radiology recommends thyroid scintigraphy when TSH levels are low to determine if a nodule is hyperfunctioning or "hot", and it is not recommended as a routine test in euthyroid patients with thyroid nodules 5, 6
• In patients with low TSH levels, thyroid scintigraphy helps identify hypofunctioning or "cold" nodules that require biopsy, and I-123 is preferred over I-131 due to its superior image quality 7
• Thyroid scintigraphy is more precise than Doppler ultrasound for measuring thyroid activity directly, and it can confirm that the entire goiter mass is composed of thyroid tissue 7

Contraindications for Thyroid Scintigraphy

• The American College of Radiology states that thyroid scintigraphy is not useful in euthyroid patients to determine malignancy or decide the need for biopsy, and it has a low positive predictive value for malignancy 5, 6
• Thyroid scintigraphy is not recommended as a screening method for thyroid cancer, and it should not be performed as a routine detection test 8

Special Considerations

• Thyroid scintigraphy can be useful in planning treatment with radioactive iodine, and it may be indicated in patients with suppressed or low TSH levels 7
• The American College of Radiology notes that thyroid scintigraphy cannot distinguish between follicular adenoma and thyroid adenocarcinoma, and it does not replace the evaluation of suspicious ultrasound characteristics 8
• The use of iodinated contrast media can temporarily affect thyroid function and the accuracy of thyroid scintigraphy 6

Thyroid Ultrasound in Thyroiditis: Clinical Recommendation

Initial Evaluation Approach

• The American College of Radiology recommends that the evaluation of thyroiditis should begin with thyroid function tests, particularly TSH measurement, before considering any imaging, and ultrasound should be performed when there is a palpable thyroid nodule, atypical presentation, or concern for coexisting thyroid malignancy 9

Ultrasound Indications and Findings

• The American College of Radiology suggests that ultrasound is the appropriate first-line imaging to confirm thyroid origin and characterize morphology in suspected goiter with obstructive symptoms, such as dyspnea, orthopnea, dysphagia, or dysphonia 9

Role of Other Imaging Modalities

• The American College of Radiology states that radionuclide scanning has no role in the routine evaluation of thyroiditis unless TSH is suppressed and differentiation between causes of thyrotoxicosis is needed, and CT or MRI are not indicated for initial thyroiditis evaluation unless there is suspected substernal extension with respiratory compromise 9

Thyroid Ultrasound for Thyroiditis

Initial Diagnostic Approach

• Most thyroiditis cases can be diagnosed clinically with laboratory confirmation alone, using thyroid function tests such as TSH measurement, as guided by the American College of Radiology 10
• Imaging does not help differentiate among causes of hypothyroidism in adults, as stated by the American College of Radiology 10

Diagnostic Value of Ultrasound

• Doppler ultrasound can differentiate overactive thyroid from destructive thyroiditis, with sensitivity 95% and specificity 90%, according to the American College of Radiology 10
• However, radionuclide uptake study remains preferred as it directly measures thyroid activity rather than inferring from blood flow, as recommended by the American College of Radiology 10

Appropriate Use of Ultrasound

• Ultrasound is not routinely necessary for straightforward cases of thyroiditis diagnosed by clinical presentation and thyroid function tests, but may be useful in certain scenarios, as suggested by the American College of Radiology 10
• The American College of Radiology recommends against using ultrasound for routine hypothyroidism workup in adults, as it does not differentiate causes and all show decreased radioiodine uptake 10
• Ultrasound is also not recommended for screening purposes without specific clinical indication, as stated by the American College of Radiology 10

Thyroid Gammagraphy Findings in Multinodular Goiter

Indications for Thyroid Gammagram

• The American College of Radiology recommends thyroid gammagram when there is thyrotoxicosis (suppressed TSH) to differentiate between toxic multinodular goiter, toxic adenoma, Graves' disease, and thyroiditis 11
• The American College of Radiology suggests thyroid gammagram for planning radioactive iodine therapy in cases of toxic multinodular goiter 11

Gammagraphic Patterns

• In non-toxic multinodular goiter (euthyroid), the gammagram typically shows heterogeneous uptake with multiple areas of variable activity distributed throughout the gland 11
• In toxic multinodular goiter, the gammagram shows multiple "hot" (hypercaptating) areas corresponding to autonomous hyperfunctioning nodules 11
• The American College of Radiology notes that the gammagram has low positive predictive value for malignancy and does not help decide which nodules to biopsy 11

Thyroid Ultrasound for Hyperthyroidism Diagnosis and Treatment

Ultrasound Findings and Their Implications

• The size and shape of a patient's thyroid gland can be assessed through ultrasound, which is necessary to determine if the gland is enlarged uniformly or if one side is bigger than the other 12
• Ultrasound can identify nodules, some of which can be "hot" (overactive) and cause hyperthyroidism, particularly in conditions like toxic adenoma or toxic multinodular goiter 13
• The blood flow pattern in the thyroid can be evaluated using Doppler ultrasound, indicating increased blood flow in overactive glands like Graves' disease or decreased blood flow in cases of inflammation or thyroiditis 13
• Ultrasound can detect suspicious features, ensuring that nodules concerning for cancer are not overlooked 13

Guiding Treatment with Ultrasound

• The American College of Radiology recommends ultrasound as the first imaging test after checking thyroid blood tests (TSH) when evaluating hyperthyroidism, as it provides detailed images of thyroid structure and is safe, readily available, and quick 13
• Ultrasound measurements of thyroid size help calculate the correct dose of radioactive iodine treatment 13
• The combination of ultrasound appearance and blood flow patterns helps distinguish between different causes of hyperthyroidism, such as Graves' disease, toxic nodules, or thyroiditis 13

Thyroid Ultrasound and Radioiodine Uptake Scan for Hyperthyroidism Diagnosis

Diagnostic Approach

• Elevated T4 and T3 levels are associated with hyperthyroidism, as indicated by a study published in the Annals of Internal Medicine 14
• Ultrasound excels at structural assessment and identifies suspicious nodules that may require biopsy to exclude malignancy, even in hyperthyroid patients, as recommended by the American College of Radiology 15

Diagnostic Pitfalls

• Coexisting thyroid nodules requiring biopsy for malignancy evaluation can be missed if ultrasound is skipped and the patient proceeds directly to uptake scan, as warned by the American College of Radiology 15
• Structural abnormalities that alter treatment decisions, such as substernal extension or compressive features, can be identified through ultrasound, as noted by the American College of Radiology 15

Radioactive Iodine Uptake in Thyroid Nodules

Clinical Implications

• The American College of Radiology indicates that a hot nodule causing thyrotoxicosis can be treated with radioactive iodine therapy, which has a 98% success rate and a 6% risk of hypothyroidism when extranodular uptake is prevented, as reported in the Journal of the American College of Radiology 16
• Radioiodine therapy for a hot nodule can cause significant nodule volume reduction, with a mean 32% reduction at 6 months, most occurring in the first 3 months, according to the Journal of the American College of Radiology 16

Diagnostic Differentiation

• The Journal of the American College of Radiology states that radioiodine imaging can help differentiate toxic adenoma from other causes of thyrotoxicosis like Graves disease, toxic multinodular goiter, or thyroiditis 16

Diagnostic Approach to Distinguishing Toxic Goitre from Sick Euthyroid Syndrome

Initial TSH Assessment

• The American College of Radiology recommends measuring serum TSH as the first step in any patient with suspected thyroid dysfunction; a suppressed (low) TSH identifies thyrotoxicosis and triggers further imaging, whereas a normal or elevated TSH in a critically ill patient indicates sick‑euthyroid syndrome and does not require thyroid‑specific therapy 17.

• A TSH value < 0.4 mIU/L is considered suppressed and should prompt evaluation for toxic goitre, because low TSH reliably signals hyperthyroidism 18.

Imaging Recommendations After a Suppressed TSH

• The American College of Radiology advises performing a thyroid ultrasound immediately after confirming a suppressed TSH; ultrasound assesses gland morphology, detects nodules, and identifies suspicious features that may require biopsy 18.

• Following ultrasound, a radioiodine uptake scan (preferably I‑123 rather than I‑131) should be obtained to differentiate the underlying cause of thyrotoxicosis (e.g., toxic multinodular goitre, Graves’ disease, or destructive thyroiditis) 18.

Clinical Indicators Supporting Toxic Multinodular Goitre

• In patients with a palpable nodular thyroid gland and compressive symptoms such as dyspnea, orthopnea, dysphagia, or dysphonia, the American College of Radiology notes that toxic multinodular goitre is the most likely diagnosis 17.