Assessment of thyroid lesions (general)

Assessment of thyroid lesions is commonly encountered in radiological practice.

Thyroid mass

• hyperplastic/colloid nodule/nodular hyperplasia: 85%

• adenoma

  • follicular: 5%

  • others: rare

• primary thyroid cancers (carcinoma)

  • papillary: 60-80% of carcinomas

  • follicular: 10-20%

  • medullary: 5%

  • anaplastic: 1-2%

• other malignancies

  • thyroid lymphoma: 1%

  • metastases to the thyroid: 1%

  • SCC: rare

• others

  • fat-containing thyroid lesions

    • adenolipoma of the thyroid gland

    • liposarcoma of the thyroid gland

Risk factors for malignancy

• 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.

Clinical featurespresentation

Thyroid enlargement: The patients complain of a visible swelling in the neck, a heavy feeling and discomfort when swallowing, or difficulty with respiration. They sometimes awake with a start for shortness of breath just after having fallen asleep. Occasionally they may complain about vague, irritating pain. 

The enlarged thyroid may present as a midline neck swelling that moves on swallowing. Asymmetry may suggest nodularity. Tracheal deviation may also be noted.

The mass may be diffusely enlarged with hyperthyroidism (Graves / Thyroiditis) or normal function (Colloid Goitre or iodine deficiency). The mass may show multinodularity with hyperfunction of secondary hyperthyroidism or mutinodularity with normal function of multinodular hyperplasia.

There maybe a single autonomically hyperfunctioning adenoma or a single nodule with 'relatively normal function' of an adenoma, cyst or carcinoma. 

A painful thyroid may represent thyroiditis, anaplastic carcinoma or colloidal haemorrhage.

Hypothyroidism: patients may have changes in weight and thinning of body hair.

Hyperthyroidism: patients may have bulging eyes and disturbances in vision, raised metabolic rate, tachycardia, or anxiety and tremor. 

Radiographic features

Ultrasound

• 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)

Nuclear medicine

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 FNA 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

  • require excisional biopsy because of overlap between

    • hyperplastic nodule

    • follicular adenoma

    • follicular carcinoma

    • follicular variant of papillary carcinoma

• atypia of uncertain significance / follicular lesion of uncertain significance (AUS/FLUS)

  • 3-6% of all FNA

  • 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

Staging

• see: thyroid cancer staging