Ultrasound in the Management of Malignant Thyroid Cancer
Ultrasound is essential for the initial evaluation and long-term management of malignant thyroid cancer, serving as the first-line imaging modality for diagnosis, treatment planning, and surveillance. 1
Diagnostic Role of Ultrasound
Initial Assessment
- Thyroid and central neck ultrasound is mandatory for all patients with suspected thyroid cancer 1, 2
- Lateral neck ultrasound should also be performed to evaluate for lymph node metastases 1
- Ultrasound should be performed before any other imaging studies or interventions 1
Ultrasound Features Suggestive of Malignancy
- Hypoechogenicity (darker appearance compared to normal thyroid tissue)
- Microcalcifications (tiny bright echogenic foci)
- Absence of peripheral halo
- Irregular borders
- Solid composition
- Central hypervascularity
- Taller-than-wide shape 1, 2
Fine Needle Aspiration (FNA)
- FNA should be performed for any thyroid nodule >1 cm
- FNA is also indicated for nodules <1 cm if there are suspicious clinical features or ultrasound characteristics 1, 2
- Ultrasound-guided FNA significantly improves diagnostic accuracy compared to palpation-guided FNA 3, 4
Treatment Planning
Preoperative Assessment
- Ultrasound is crucial for accurate staging and surgical planning 1
- The extent of surgery depends on ultrasound findings:
- Total thyroidectomy is indicated for tumors >4 cm, extrathyroidal extension, cervical lymph node metastases, or distant metastases
- Lobectomy may be considered for tumors ≤4 cm without evidence of extrathyroidal extension or lymph node involvement 1
Lymph Node Mapping
- Ultrasound should map central and lateral neck compartments to identify suspicious lymph nodes 1, 4
- Suspicious lymph node features include:
- Round shape (loss of normal oval shape)
- Loss of fatty hilum
- Peripheral or disorganized vascularity
- Microcalcifications
- Cystic changes 5
- Suspicious lymph nodes should undergo ultrasound-guided FNA with thyroglobulin washout 1
Post-Treatment Surveillance
- Regular ultrasound surveillance is the cornerstone of follow-up after thyroid cancer treatment 2, 6
- Frequency of surveillance depends on risk stratification:
- Low-risk patients: Optional ultrasound after 3-5 years
- Intermediate-risk patients: Every 6-12 months
- High-risk patients: Every 3-6 months 2
- Ultrasound should be combined with serum thyroglobulin measurement for optimal surveillance 2
- Ultrasound can detect local recurrence and regional lymph node metastases, which are the most common sites of recurrence 7, 6
Limitations and Complementary Imaging
- Ultrasound has limited ability to evaluate:
- Retrosternal extension
- Invasion of deep structures (trachea, esophagus)
- Retropharyngeal, parapharyngeal, and retrotracheal lymph nodes 7
- CT or MRI should be considered for fixed, bulky, or substernal lesions 1
- For radioiodine-refractory differentiated thyroid cancer, additional imaging modalities may be needed for systemic staging 8
Pitfalls to Avoid
- Relying solely on a single ultrasound feature to determine malignancy risk (use constellation of features) 3, 5
- Failing to perform ultrasound-guided FNA on suspicious nodules
- Overlooking small but suspicious lymph nodes during surveillance
- Inadequate documentation of nodule characteristics for comparison during follow-up 5
- Not considering complementary imaging when ultrasound findings suggest extensive disease
By implementing comprehensive ultrasound evaluation in the management of thyroid cancer, clinicians can optimize diagnosis, treatment planning, and long-term surveillance to improve patient outcomes.