When is a neck ultrasound recommended for a patient with symptoms suggestive of thyroid or lymph node abnormalities?

Neck Ultrasound for Thyroid and Lymph Node Abnormalities

When to Order Neck Ultrasound

Neck ultrasound is the first-line imaging study for any patient with a palpable thyroid nodule, suspected goiter, thyrotoxicosis, or concern for cervical lymphadenopathy, and should be performed before any other imaging modality. 1

Primary Indications for Neck Ultrasound

Thyroid Nodule Evaluation

• Any palpable thyroid nodule in a euthyroid patient requires neck ultrasound as the initial imaging study to confirm the abnormality is within the thyroid and characterize malignancy risk 1
• Ultrasound provides high-resolution imaging superior to CT or MRI for detecting and characterizing thyroid nodules, including those as small as 5mm 1, 2
• The National Comprehensive Cancer Network recommends ultrasound of the thyroid and central neck as part of initial workup for thyroid disorders, even without palpable abnormalities, since approximately 50% of malignant thyroid nodules are asymptomatic 3

Suspected Goiter

• Ultrasound confirms the diagnosis when patients present with diffuse palpable neck abnormality or obstructive symptoms (dyspnea, orthopnea, dysphagia, dysphonia) 1
• It documents size, extent, and morphology of the goiter, and evaluates for suspicious nodules within the goiter 1

Thyrotoxicosis Workup

• After confirming suppressed TSH with laboratory testing, ultrasound evaluates thyroid morphology and identifies potential nodules to help determine the etiology of hyperthyroidism 3
• Ultrasound findings guide decisions for fine-needle aspiration based on nodule characteristics 3

Surveillance for Thyroid Cancer Recurrence

• Ultrasound of the neck is the first imaging investigation for suspected differentiated thyroid cancer (DTC) or medullary thyroid cancer (MTC) recurrence, including evaluation of the thyroid bed and cervical nodes 1
• It can characterize palpable abnormalities and detect deeper neck masses that are not palpable 1
• For MTC with calcitonin levels <150 pg/mL, ultrasound alone is generally adequate as disease is usually limited to the neck 1

Critical Ultrasound Features That Trigger Further Action

Suspicious Sonographic Features for Malignancy

• Microcalcifications (highly specific for papillary thyroid carcinoma) 3, 4
• Marked hypoechogenicity (solid nodules darker than surrounding thyroid parenchyma) 3, 4
• Irregular or microlobulated margins (infiltrative borders rather than smooth contours) 3, 4
• Absence of peripheral halo (loss of thin hypoechoic rim) 3, 4
• Central hypervascularity (chaotic internal vascular pattern) 3, 4
• Solid composition (versus cystic) 3, 4

When Ultrasound Findings Mandate FNA

• Any nodule >1 cm with ≥2 suspicious ultrasound features 4
• Any nodule <1 cm with suspicious features PLUS high-risk clinical factors (history of head/neck irradiation, family history of thyroid cancer, age <15 years, male gender) 3, 4
• Any nodule >4 cm regardless of ultrasound appearance (due to increased false-negative rate) 4
• Suspicious cervical lymphadenopathy detected on ultrasound 3, 4

Lymph Node Assessment

Comprehensive neck ultrasound must include evaluation of central and lateral cervical lymph node compartments, not just the thyroid gland 3, 5

• Ultrasound has superior specificity (92%) compared to CT (25%) for evaluating cervical lymph nodes in thyroid cancer patients 1
• Detection of suspicious lymph nodes may alter surgical management, particularly in patients with thyroid nodule microcalcifications or higher Bethesda category on FNA 5
• Preoperative lymph node assessment is essential for surgical planning in confirmed or suspected thyroid malignancy 4

Common Pitfalls to Avoid

Do not skip ultrasound evaluation in patients without palpable abnormalities, as this may lead to delayed diagnosis of thyroid malignancies that are not clinically apparent 3

Do not proceed directly to radionuclide scanning without first performing ultrasound, as this may miss important structural abnormalities 3

Do not perform only thyroid-focused ultrasound without evaluating surrounding lymph nodes, as incomplete assessment can miss metastatic disease 3, 5

Do not use CT or MRI as initial imaging for thyroid nodule characterization, as ultrasound is superior for this purpose and neither CT nor MRI can reliably differentiate benign from malignant nodules unless there is gross invasion 1

When Cross-Sectional Imaging Supplements Ultrasound

CT or MRI of the neck has a role after ultrasound in specific circumstances 1:

• Suspected substernal goiter extension 1
• Concern for invasive thyroid cancer into surrounding structures 1
• Detection of additional metastases in the central compartment, mediastinum, or behind the trachea 1
• Assessment for tumor vascular encasement 1

Algorithm for Clinical Decision-Making

1. Obtain thyroid function tests (TSH, free T4/T3) 3
2. Perform high-resolution neck ultrasound evaluating:
   • Thyroid gland morphology 3
   • Presence and characteristics of nodules 3
   • Central and lateral cervical lymph nodes 3
3. If nodules detected, assess for suspicious features (microcalcifications, hypoechogenicity, irregular margins, solid composition, central hypervascularity) 3, 4
4. Proceed to ultrasound-guided FNA if criteria met based on size and suspicious features 3, 4
5. Consider cross-sectional imaging only for specific indications (substernal extension, suspected invasion, high-risk recurrence surveillance) 1