Thyroid Ultrasound in Thyroiditis: Clinical Recommendation
Thyroid ultrasound is not routinely indicated for uncomplicated thyroiditis but should be performed when there is a palpable thyroid nodule, atypical presentation, or concern for coexisting thyroid malignancy.
Initial Evaluation Approach
The evaluation of thyroiditis should begin with thyroid function tests, particularly TSH measurement, before considering any imaging 1. The clinical presentation and TSH results will guide whether imaging is necessary 2, 1.
When Ultrasound IS Indicated in Thyroiditis
Palpable thyroid nodule present: Even in the setting of painless (lymphocytic) thyroiditis, ultrasound should be performed if a discrete palpable nodule is detected, as thyroid carcinoma can coexist with thyroiditis 3
Atypical clinical features: Subacute thyroiditis can present with focal thyroid lesions that mimic suspicious nodules on ultrasound, and imaging helps differentiate these from true malignancy 4
Hashimoto thyroiditis with nodules: Ultrasound-guided fine-needle aspiration is particularly valuable in this setting, as it can distinguish between benign nodules, pseudotumor, and malignancy (including lymphoma) with 100% sensitivity 5
Suspected goiter with obstructive symptoms: If thyroiditis presents with dyspnea, orthopnea, dysphagia, or dysphonia suggesting mass effect, ultrasound is the appropriate first-line imaging to confirm thyroid origin and characterize morphology 2, 6
When Ultrasound Is NOT Routinely Indicated
Uncomplicated subacute thyroiditis: In classic presentations with diffuse thyroid tenderness, elevated ESR, and biochemical hyperthyroidism without palpable discrete nodules, imaging may be deferred 4
Euthyroid or hypothyroid patients without nodules: When TSH is normal or elevated and there are no palpable abnormalities, imaging is generally not indicated 1
Critical Clinical Pitfalls
Timing of ultrasound matters: Subacute thyroiditis produces transitory ultrasound changes (focal or multifocal hypoechoic areas, heterogeneous echogenicity) that can obscure or mimic papillary carcinoma 3, 4. If ultrasound is performed during active inflammation, suspicious findings may resolve with clinical recovery 3, 4.
However, delaying ultrasound risks missing coexisting malignancy. The optimal approach is to perform initial ultrasound when a palpable nodule is present, particularly looking for 3:
- Discrete nodules with suspicious features (microcalcifications, irregular margins)
- Hypoechoic areas >1 cm with microcalcifications
- Cervical lymphadenopathy
Ultrasound Findings Requiring Further Action
If ultrasound is performed and reveals suspicious features, fine-needle aspiration should be pursued despite the thyroiditis diagnosis 3, 5. Key concerning features include:
- Hypoechoic nodules (most carcinomas appear hypoechoic) 5
- Markedly hypoechoic masses (concerning for lymphoma in Hashimoto thyroiditis) 5
- Microcalcifications within nodules or heterogeneous parenchyma 3
- Cervical lymphadenopathy 3
Note that hyperechoic nodules are usually benign, and isoechoic nodules have only 13% malignancy frequency 5.
Role of Other Imaging Modalities
Radionuclide scanning has no role in the routine evaluation of thyroiditis unless TSH is suppressed and differentiation between causes of thyrotoxicosis (Graves disease, toxic adenoma, toxic multinodular goiter versus thyroiditis) is needed 2, 1. It cannot determine malignancy risk and should not be used for this purpose in euthyroid patients 1.
CT or MRI are not indicated for initial thyroiditis evaluation unless there is suspected substernal extension with respiratory compromise 2, 6.