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Thyroid

Anatomy

Strap muscles are anterior to thyroid (Sternohyoid, Sternothyroid, Omohyoid). Carotid arteries are lateral to each thyroid lobe and Jugular veins are lateral to the carotids, longus coli muscle posteriorly. Normal thyroid is homogeneous, hyperechoic.


Lingual thyroid

Ectopic thyroid tissue between foramen cecum of tongue and the epiglottis.


Thyroglossal duct cyst

Most common congenital cyst in the neck. Cystic lesion w/ low level echoes. Midline, between thyroid and hyoid bone. More caudad, more likely to be lateral to the midline.


Thyroid Nodules

Extremely common and are most common indication for thyroid US. 50% of population, prevalence increases w/ age: % = age - 10; Malignant tumors are very low incidence, only 2%.

Nodular Hyperplasia

The most common cause for thyroid nodules.

  1. Hyperplastic nodules
  2. Adenomas
  3. Colloid nodule

Radiologic description: always describe as nodule, not as lesion or mass.
Examples:

  • Hypoechoic nodule, predominantly solid w/ multiple small cystic spaces (+/-) w/ inspisated colloid (comet-tail artifacts will distinguish it from calcs).
  • Large isoechoic nodule w/ honeycomb pattern
  • Complex nodule w/ cysts and solid components
  • Predominantly cystic nodule w/ thick septations and low level internal echoes
  • Predominantly cystic nodule w/ thick wall and prominent solid mural nodule

Follicular adenomas

5-10% of nodules, solid, range from hypo to hyperechoic, hypoechoic halo, cannot be distinguished from follicular cancer by FNA, need surgical resection


Thyroid Cancer

Papillary 75%, Follicular 10%, Medullary 5%, Anaplastic 5%, Hurthle cell ca


Papillary thyroid cancer

75%. More common in < 40 yo and women, cervical nodal mets (does not affect prognosis), excellent prognosis at 95% survival at 20 years. Hypoechoic and entirely solid, microcalcifications in psammoma bodies (in thyroid nodule and lymph nodes), mixed papillary/follicular variant behaves as papillary ca.


Follicular thyroid cancer

10%, women in 6th decade, minimally and widely invasive forms, spreads hematogenously into the bone, brain, lung and liver, rarely into neck nodes (distinguishing sign from papillary ca), 20 y mortality is 25%. Frequently coexist w/ multinodular goiters. Solid, heterogeneous, hypoechoic, no microcalcs. Cannot be distinguished from follicular adenoma or w/ FNA


Medullary thyroid cancer

5%, form C cell secreting calcitonin (tu marker), MEN II, more aggressive, does not respond to chemo or radiation th. Hypoechoic solid mass, microcalcs in nodules and lymph nodes.


Anaplastic thyroid cancer

5%, > 60, dismal prognosis, 5y mortality > 95%. Large solid hypoechoic mass, local invasion at the time of presentation.


Thyroid lymphoma

5%, non-Hodgkin, elderly W, rapidly growing large, solid, hypoechoic


Metastases

Lung, breast, RCC. Solid nodule.


Benign features

Cystic elements, Hyper or isoechoic, Peripheral thin and regular hypoechoic halo, Eggshell calcs, Inspissated colloid, Multiplicity


Malignant features

Entirely Solid, Hypoechoic, Microcalcifications, Cervical LA, Thick peripheral hypoechoic halo, LN w/ microcalcs


Hashimoto thyroiditis

Ab against thyroglobulin - serologic dx, most common cause of hypothyroidism, 40-60yo, W>>>M, slight increased risk for Lymphoma. Enlarged, hypoechoic, heterogeneous gland, thin echogenic fibrous strands may cause a multilobulated or micronodular appearance, hypervascular, nodules and mlg nodules can coexist


Graves disease

Most common cause of hyperthyroidism, TSH Ig, serologic dx Enlarged gland, diffuse hypoechogenicity, heterogeneity, hypervascularity (thyroid inferno)


Subacute thyroiditis, De Quervain’s thyroiditis

Viral, enlarged, painful thyroid, fever poorly marginated area of hypoechogenicity in the involved region of thyroid