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Assessment of thyroid lesions

Assessment of thyroid lesions is commonly encountered in radiological practice.

Thyroid mass breakdown
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

For an imaging pathway on how to work up a thyroid nodule: see reference 6

Ultrasound
  • hyperechoic solid nodule - 5% chance of being malignant
  • isoechoic solid nodule - 25% (follicular and medullary)
  • hypoechoic solid nodule - 65% (anaplastic and lymphoma) reference required
  • 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

Size criteria for indication for FNA according American thyroid association - 2009 10

  • high risk history 
    • with suspicious sonographic features: >5 mm
    • without suspicious sonographic features: >5 mm
    • with abnormal cervical lymph nodes: all; FNA may be obtained from the lymph node as well
    • with microcalcifications: ≥1 cm
  • solid nodule
    • hypoechoeic: >1 cm
    • solid nodule - iso or hyperechoeic: ≥1-1.5 cm
  • mixed cystic-solid nodule 
    • with suspicious sonographic features: ≥1.5-2 cm
    • without suspicious sonographic features: ≥2 cm
  • spongiform nodule: ≥2 cm
  • purely cystic - FNA not indicated

High risk factors

  • history of childhood head and neck irradiation
  • family history of thyroid cancer or a thyroid cancer syndrome
  • prior hemithyroidectomy with discovery of thyroid cancer
  • increased activity on PET scan
  • presence of MEN-2 associated oncogene

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

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