Overview
This lecture covers the ultrasound appearances of the thyroid gland, distinguishing between normal anatomy and various thyroid pathologies, including nodular, malignant, and parenchymal diseases.
Thyroid Anatomy & Normal Ultrasound Appearance
- The thyroid gland comprises two lobes (right and left) connected by the isthmus, located in the neck.
- The thyroid appears hyperechoic (bright) on ultrasound.
- The trachea is posterior to the thyroid and casts acoustic shadows due to air.
- Strap muscles are anterior to the thyroid; common carotid arteries appear as anechoic (dark) circular structures.
Thyromegaly (Goiter)
- Thyromegaly is defined by an anterior-posterior (AP) diameter >2 cm and isthmus thickness >4 mm.
- The normal thyroid lobe length is about 4 cm; values above this suggest thyromegaly.
- Thyromegaly is also termed "goiter" and can result from hyperplasia, cancer, or thyroiditis.
Nodular Thyroid Disease
- Nodular hyperplasia may show cystic components, septations, thick walls, mural nodules, and may be hypervascular on color Doppler.
- Colloid nodules have cystic lesions with echogenic colloid crystals and may show comet tail artifacts; these are usually benign.
Thyroid Neoplasms
- Follicular adenoma appears as a hypoechoic (darker) mass with a hypoechoic halo and may be malignant.
- Follicular carcinoma shows a hypoechoic nodule, hypoechoic halo, cystic areas, and sometimes calcifications.
- Papillary carcinoma is the most common thyroid cancer, usually hypoechoic with possible calcifications, cystic, or solid components, and shows posterior acoustic shadowing.
- Anaplastic cancer presents as large hypoechoic masses that can displace nearby vessels.
- Lymphoma causes enlargement and heterogeneous echotexture in the thyroid.
- Thyroid metastases have variable solid, heterogeneous appearances depending on the primary cancer.
Parenchymal Thyroid Diseases
- Hashimoto’s thyroiditis causes hypothyroidism, thyroid enlargement, and scattered hypoechoic nodules; shows "thyroid inferno" (hypervascularity) on Doppler.
- Graves’ disease causes hyperthyroidism, an enlarged and more homogeneous thyroid with less heterogeneity than Hashimoto’s; may also show "thyroid inferno."
- Subacute (De Quervain’s) thyroiditis affects both lobes with hypoechoic areas bilaterally.
Key Terms & Definitions
- Hyperechoic — appearing brighter than surrounding tissue on ultrasound.
- Anechoic — appears black on ultrasound, indicating fluid or blood.
- Thyromegaly/Goiter — abnormal enlargement of the thyroid gland.
- Nodular hyperplasia — benign overgrowth of thyroid tissue causing nodules.
- Colloid nodule — benign cystic nodule containing colloid material.
- Follicular adenoma/carcinoma — benign/malignant follicular cell tumors of the thyroid.
- Papillary carcinoma — most common malignant thyroid tumor, often with calcifications.
- Hashimoto’s thyroiditis — autoimmune thyroid disease causing hypothyroidism.
- Graves’ disease — autoimmune disease causing hyperthyroidism.
- Thyroid inferno — markedly increased blood flow on Doppler imaging.
Action Items / Next Steps
- Review ultrasound images of thyroid pathologies for visual recognition.
- Prepare for further study on clinical and laboratory correlation with ultrasound findings.