Assessment of thyroid lesions (ultrasound)

Ultrasound along with nuclear medicine, is an important modality for assessment of thyroid lesions, and it is also frequently used to guide biopsy. Diagnostic criteria for thyroid nodules continue to evolve with improving ultrasound technology.

Radiographic features

Ultrasound
Calcification

Although calcification can be seen in both benign and malignant processes, it is the ultrasound feature most closely associated with malignancy 1.

Echogenicity
  • hypoechoic solid nodule
    • most papillary thyroid carcinomas
    • nearly all medullary thyroid carcinomas 3
    • benign nodules can be hypoechoic
    • if no other malignant features (e.g. calcifications) then hypoechoic nodules are typically biopsied after reaching size criteria
  • isoechoic solid nodule: 25% (follicular and medullary)
  • hyperechoic solid nodule: 5% chance of being malignant
  • large cystic component favours a benign entity although a significant proportion of papillary carcinomas will have a cystic component
  • while a halo around a well-marginated hypoechoic or isoechoic nodule is typical of a follicular adenoma 3, it is absent in >50% of benign nodules 2 ; what is more, up to 24% of papillary thyroid carcinomas may have a halo, be it complete or incomplete 2

Colour Doppler

  • intranodular flow usually malignant
  • lymph nodes with increased colour Doppler flow are suspicious

Other

  • invasion of local structures favors anaplastic thyroid carcinoma and thyroid lymphoma
  • shadowing around the edges of a nodule (edge refraction shadow) are associated with papillary thyroid carcinoma 3
  • a nodule taller than it is wide is suspicious for malignancy 4
  • irregular margins are suspicious for malignancy 4

Lymph nodes

  • enlarged regional lymph nodes are suspicious for thyroid malignancy, esp. papillary thyroid carcinoma
  • microcalcifications in regional lymph nodes are highly suspicious
  • lymph nodes with cystic change are highly suspicious
  • loss of normal fatty hilum, irregular node appearance
  • increased colour Doppler flow is suspicious
  • no threshold criteria for lymph node biopsy
    • biopsy if suspicious features
    • consider biopsy if >8 mm
Sonographic features favouring a benign nodule
  • large cystic component
  • hyperechoic solid
  • comet tail artefact
Sonographic features favouring a malignant nodule
  • hypoechoic solid
  • presence of microcalcifications: almost always warrants a FNA
  • local invasion of surrounding structures
  • taller than it is wide
  • large size: the cut off is often taken as 10 mm to warrant a FNA
  • suspicious neck lymph nodes suggesting metastatic disease
  • intranodular blood flow

Treatment and prognosis

No sonographic features are 100% sensitive or specific (although lymphadenopathy with microcalcifications is 100% specific). The differential for a suspicious nodule includes benign nodules such as adenomatoid nodules, follicular adenoma, and Hashimoto thyroiditis. Parathyroid adenomas are also a confounding nodule.

A suspicious nodule (and lymph node, if applicable) should undergo fine needle aspiration (FNA).

Size criteria for biopsy

Multiple criteria exist from societies in different subspecialties. The nodule's features are important in deciding for whether and when to biopsy. Biopsy thresholds vary among institutions. The ATA guidelines are often followed in clinical practice.

See: assessment of thyroid lesions (general) for more information

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Article Information

rID: 35024
System: Head & Neck
Section: Approach
Synonyms or Alternate Spellings:
  • Thyroid nodules on ultrasound
  • Thyroid nodules - ultrasound

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