The Thyroid and Parathyroid Glands

Vocabulary-style flashcards covering the anatomy, physiology, and pathology of the thyroid and parathyroid glands based on the lecture notes.

Anatomy of the Thyroid Gland location

Located in the anteroinferior neck at the level of the thyroid cartilage.

Isthmus

The structure that connects the right and left lobes of the thyroid gland.

Pyramidal lobe

A lobe that arises from the isthmus of the thyroid gland.

Normal adult thyroid dimensions

$40-60 imes 20 imes 13-18\,mm$.

Ellipsoid formula

A method to calculate thyroid volume for each lobe using $ext{length} imes ext{width} imes ext{thickness} imes 0.52$.

Normal mean thyroid volume

$18.6 \pm 4.5\,ml$.

Strap muscles

Muscles located on the anterior surface of the thyroid, including the sternothyroid, omohyoid, and sternohyoid.

Sternocleidomastoid muscle

A larger oval band that lies anterior and lateral to the thyroid gland.

Longus colli muscle

A hypoechoic triangular structure posterior and lateral to the thyroid lobes, adjacent to cervical vertebrae.

Esophagus sonographic appearance

Identified by a target appearance in the transverse plane and by peristaltic movements when the patient swallows; primarily a midline structure that may be found to the left of the trachea.

Superior thyroid arteries

Two arteries that arise from the external carotids and descend to the upper poles of the thyroid.

Inferior thyroid arteries

Two arteries that arise from the thyrocervical trunk of the subclavian artery and ascend to the lower poles of the thyroid.

Major thyroid artery Doppler velocities

Peak systolic velocities reaching $20-40\,cm/sec$.

Thyroid hormone synthesis mechanism

The mechanism for producing thyroid hormones is iodine metabolism.

Triiodothyronine ($T_3$) and Thyroxine ($T_4$)

Hormones produced by the thyroid gland through iodine metabolism chemical reactions.

Thyrotropin (TSH)

Thyroid-stimulating hormone produced by the pituitary gland that triggers the release of thyroid hormones into the bloodstream.

Calcitonin

A hormone that helps maintain homeostasis of blood calcium by inhibiting bone breakdown to decrease calcium concentration in the blood.

Euthyroid

The condition of the thyroid when it is producing the correct amount of thyroid hormone.

Hypothyroidism

Undersecretion of thyroid hormones, which can cause clinical signs such as weight gain, hair loss, lethargy, and myxedema.

Hyperthyroidism

Oversecretion of thyroid hormones, which dramatically increases metabolic rate and can cause weight loss, tremors, palpitations, and exophthalmos.

Exophthalmos

Protruding eyes, often seen in patients with hyperthyroidism.

Preferred thyroid transducer

A high-frequency ($7.5-15\,MHz$) linear-array transducer.

Goiter

The most common thyroid abnormality; an enlargement of the gland caused by iodine deficiency or compensatory hypertrophy.

Toxic goiter

A hyperthyroid condition resulting from hyperactivity of the thyroid gland.

Nontoxic (simple) goiter

Diffuse thyroid enlargement not resulting from neoplasm or inflammation and not initially associated with hypo- or hyperthyroidism.

Thyroid Cyst

Cystic degeneration of a follicular adenoma; approximately $20\%$ of solitary nodules are cystic.

Adenoma (Thyroid)

A benign thyroid neoplasm characterized by complete fibrous encapsulation and compression of adjacent tissue.

Thyroid Adenoma Halo

A thin echolucent rim surrounding the lesion, representing edema of compressed normal tissue or the capsule.

Papillary Carcinoma

The most common thyroid malignancy; features include hypoechogenicity, microcalcifications (tiny, punctate hyperechoic foci), and hypervascularity.

Follicular Carcinoma

Malignancy that may be minimally invasive (encapsulated) or widely invasive; suspected when a thick irregular halo and tortuous internal blood vessels are present.

Medullary Carcinoma

Accounts for $5\%$ of thyroid cancers; often familial ($20\%$) and an essential component of multiple endocrine neoplasia (MEN) type II syndromes.

Anaplastic Carcinoma

A rare undifferentiated thyroid cancer (less than $2\%$) that usually occurs after age $50$ and presents as a hard, fixed, rapidly growing mass.

Thyroid Lymphoma

Primarily non-Hodgkin’s type; characterized by a large, nonvascular, hypoechoic, and lobulated solid mass.

Subacute Thyroiditis (de Quervain's)

Caused by a viral infection; presents with pain and swelling, potentially causing transient hyperthyroidism before the gland returns to normal function.

Hashimoto’s Thyroiditis

The most common form of thyroiditis; a painless autoimmune disorder leading to chronic inflammation, symmetric or asymmetric enlargement, and a coarsely textured parenchyma.

Thyroid inferno

A sonographic pattern of increased vascularity on color Doppler imaging, seen in Graves’ disease and sometimes hypothyroidism in Hashimoto's.

Graves’ Disease

An autoimmune disorder characterized by hypermetabolism, diffuse toxic goiter, exophthalmos, and cutaneous manifestations.

Normal Parathyroid Gland size

Usually less than $4\,mm$ (not typically seen with sonography); abnormal glands are greater than $5\,mm$.

Parathyroid Hormone (PTH)

Hormone produced by parathyroid glands to monitor serum calcium; its secretion is stimulated by a decrease in blood calcium levels.

Primary Hyperparathyroidism

State of increased function of parathyroid glands characterized by hypercalcemia, hypercalciuria, and low serum phosphate.

Primary Hyperplasia

Hyperfunction of all parathyroid glands with no apparent cause; accounts for approximately $10\%$ of hyperparathyroidism cases.

Parathyroid Adenoma

The most common cause ($80\%$) of primary hyperparathyroidism; typically oval, hypoechoic, and solid.

Secondary Hyperparathyroidism

A compensatory hyperactivity of parathyroid glands caused by chronic hypocalcemia from renal failure, vitamin $D$ deficiency, or malabsorption.

Thyroglossal Duct Cysts

Congenital anomalies appearing in the midline of the neck anterior to the trachea, resulting from a failure of the tubular development remnant to atrophy.

Branchial Cleft Cysts

Cystic formations usually located lateral to the thyroid gland, formed during embryonic development.

Neck Abscess clinical appearance

Ranges from primarily fluid-filled to completely echogenic; most commonly a complex cystic mass with irregular walls and low-level echogenicity.

Neck Adenopathy

Enlarged lymph nodes; benign nodes are usually oval with a central core echo complex, while malignant nodes tend to be more rounded.