Assessment of thyroid lesions is commonly encountered in radiological practice.
- hyperplastic / colloid nodule / nodular hyperplasia: 85%
- follicular: 5%
- others: rare
Risk factors for malignancy
- cold on thyroid scan
- past history of radiotherapy
The first three risk factors are really a reflection that elderly women with multiple benign thyroid nodules are very common.
- taller-than-wide in axial/transverse dimension, microcalcifications, local invasiveness, microlobulated contour, and hypoechogenicity are suspicious features
- size criteria are controversial and continuously evolving
- cervical lymphadenopathy is a feature
- for detailed assessment, see: assessment of thyroid lesions (ultrasound)
A single 'cold' nodule has a 10% chance of being malignant. A single 'hot' nodule has <1% chance of being malignant.
Treatment and prognosis
Indications for FNA
Each grading system provides recommendations for when FNA is indicated (see snippet for individual systems).
Both appearance and size are factors to consider.
The criteria developed by the American Thyroid Association (2015) 6 are often used in clinical practice. See: ATA guidelines for assessment of thyroid nodules.
The ACR TI-RADS system recommends FNA for TR3 lesions >25 mm, TR4 lesions >15 mm and TR5 lesions >10 mm 11.
The BTA U classification recommends FSA for any non-benign lesion (i.e. U3, U4 or U5) 12.
Additional recommendations for FNA by the American Association of Clinical Endocrinologists 4:
- FNA recommended for nodules <10 mm whenever clinical information or ultrasound features raises suspicion about the presence of a malignancy
Management of FNA results
- benign: clinical and imaging follow-up
- follicular neoplasm
- atypia of uncertain significance / follicular lesion of uncertain significance (AUS/FLUS)
- repeat FNA
- two samples obtained at second biopsy
- if AUS/FLUS again (~20%) on the first sample, then the risk of malignancy is 5-15% 10
- the second sample may be sent for gene sequencing, if available (gene expression classifier)
- if benign, then normal clinical and imaging follow-up
- if suspicious, 50% risk of malignancy
- malignant: partial or total thyroidectomy with lymph node exploration
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