Assessment of thyroid lesions

Assessment of thyroid lesions are commonly encountered in radiological practice.

Thyroid mass breakdown

• hyperplastic / colloid nodule / nodular hyperplasia: 85%
• adenoma
  • follicular: 5%
  • others: rare
• carcinoma
  • papillary: 60-80% of carcinomas
  • follicular: 10-20%
  • medullary: 5%
  • anaplastic: 5%
  • thyroid lymphoma: 1%
  • metastases to the thyroid: 1%

Risk factors of a nodule being malignant

• young
• male
• solitary
• 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.

Radiographic features

Ultrasound

• hyperechoic solid nodule - 5% chance of being malignant
• isoechoic solid nodule - 25% (follicular and medullary)
• hypoechoic solid nodule - 65% (anaplastic and lymphoma)
• large cystic component favours a benign entity although a significant proportion of papillary carcinomas will have a cystic component
• comet tail artefact is seen in colloid nodules
• intranodular flow usually malignant
• halo around isoechoic is typical of a follicular adenoma

Therefore:

Benign sonographic features

• large cystic component
• hyperechoic solid
• comet tail artefact
• halo

Malignant sonographic features

• hypoechoic solid
• intranodular blood flow
• large size: the cut off is often taken as 10mm to warrant a FNA
• presence of microcalcifications - almost always warrants a FNA

Nuclear medicine

A single 'cold' nodule has a 10% chance of being malignant A single 'hot' nodule has <1% chance of being malignant

Indications for FNA

Indications for FNA according to Society of Radiologists in Ultrasound - 2008 ⁴

• nodule 1.0 cm or more at the largest diameter if microcalcifications are present
• nodule 1.5 cm or larger if the nodule is solid or if there are coarse calcifications within the nodule

Additioanal recommendations for FNA by the American Association of Clinical Endocrinologists ⁴

• FNA recommended for nodules smaller than 10mm whenever clinical information or ultrasound features raises suspicion about the presence of a malignancy

Differential diagnosis for follicular cells on FNA

• hyperplastic nodule
• follicular adenoma
• follicular carcinoma
• follicular variant of papillary carcinoma

Therefore, follicular cells on FNA usually require excisional histology.

Staging

• see : thyroid cancer staging.