Superficial Structures- Thyroid

Thyroid gland is located in

the neck

isthmus

connects the 2 lateral lobes; narrow section

Pyramidal lobe

3rd love arising from the superior portion of the isthmus; ascends to the level of the hyoid bone

Thyroid epithelial cells

the cells responsible for synthesis of thyroid hormones

arranged in spheres called thyroid follicles

Colloid

follicles are filled with this

a proteinaceous depot of thyroid hormone precursor

Thyroid Hormones secreted

T4, T3, Calcitonin

More than _____ of the T3 and T4 circulating in blood is bound to carrier proteins

99%

calcitonin

hormone produced in the C cells of the thyroid gland which participates in calcium and phosphorus metabolism

Calcitonin reduced blood Ca++ by:

decreasing calcium absorption by intestines, increasing calcium storage in bones, increasing calcium excretion through kidneys

Control of thyroid hormone synthesis and secretion is stimulated by

TSH from anterior pituitary gland

Effects of thyroid hormone

development, growth, metabolism

Euthyroid

normal thyroid

Hypothyroidism

the under-secretion of thyroid hormones; decreased activity of thyroid gland

The most common thyroid function disorder is

hypothyroidism

Hypothyroidism can be caused by

low intake of iodine in the body

inability of the thyroid to produce enough

problem in the pituitary gland that doesn’t properly control thyroid production

Primary hypothyroidism

Most common

caused by defective hormone synthesis, endemic iodine deficiency, iodine excess, inflammatory conditions

secondary hypothyroidism

less common, caused by pituitary adenoma, tumors, irradiation, medication, congenital disorders

Signs and symptoms of hypothyroidism

weight gain, hair loss, lethargy, cold intolerance, muscle cramps, slow metabolic rate, decreased heart rate, increased subcutaneous tissue around eyes

Hyperthyroidism (thyrotoxicosis)

The over-secretion of thyroid hormones; hyperactivity of the thyroid gland

caused by elevated free T3 and T4

Underlying cause of hyperthyroidism in 50-80% of cases is

Graves Disease

Primary hyperthyroidism

form of thyrotoxicosis which excess thyroid hormone is synthesized and secreted by the thyroid itself

Secondary hyperthyroidism

rare, caused by TSH-secreting pituitary adenoma

Signs and symptoms of hyperthyroidism

nervousness, weight loss, tremors, excessive sweating, palpitations, increased heart rate, diarrhea, protruding eyes

T4 and T3 is high in

hyperthyroidism

t4 and t3 is low in

hypothyroidism

TSH is low in

hyperthyroidism

TSH is high in

hypothyroidism

We use ultrasound to

determine size of gland and mass location, differentiating between cystic and solid lesions, FNA

Sonography cant determine the difference of

benign and malignant masses

Normal size of 1 thyroid lobe length

4.0-6.0cm

Normal size of 1 thyroid lobe AP

1\.3-1.8cm

Normal size of 1 thyroid lobe width

1\.5-2cm

normal size of isthmus

4\.0-6.0mm

size of thyroid varies with

gender and body surface area

Normal ultrasound appearance of thyroid

homogenous, medium-level echo pattern

more echogenic than surrounding muscles

fibrous capsule is smooth-bordered

trachea

appears medially as a bright reflector with acoustic reverberation artifacts and shadowinge

esophagus

appears posterolateral and to the left of the trachea as a hypo echoic structure with a central echogenic center; elevates/moves with swallowing

Longus colli

located on the anterior surface of vertebral column

lies posterior to the thyroid lobe and CCA

Sternocleidomastoid muscles

lateral and superficial neck muscles

located anterior and lateral to the thyroid libes

strap muscles

group of long flat neck muscles

located anterior to the thyroid muscles

surrounding musculature appears

hypoechoic compared to normal thyroid tissue

CCA

appears anechoic

located medial to IJV, lateral to thyroid lobe

IJV

located lateral to CCA and thyroid lobe

will enlarge with valsalva maneuver

Superior thyroid artery arises from

external carotid artery

inferior thyroid artery arises from

thyrocerival artery

superior and middle thyroid veins drain into the

Internal jugular vein

inferior thyroid vein drain into the

innominate vein

Athyrosis

absence of the thyroid gland

rare

absent isthmus

complete absence of the isthmus

gland appears as 2 independent lobes

Ectopic thyroid tissue

gland development can occur ectopic anywhere along the pathway of descent

ectopic thyroid tissue is most common under

the tongue

Nodular thyroid disease (goiter)

most common thyroid abnormality

nontoxic goiter refers to

an enlargement involving the entire gland without producing nodularity and with out evidence of functional disturbance

Most common cause of nodular thyroid disease is

iodine deficiency

goiter is the term used for

enlargement of thyroid gland

a goiter may

compress the esophagus and interfere with swallowing or cause pressure on the trachea

nodular thyroid disease are

mostly isoechoic compared to normal thyroid, but as gland enlarges, becomes more hyperechoic

fibrosis or calcification may be present

True epithelium-lined cysts in the thyroid are

uncommon and are almost always benign

thyroid cysts are

cystic degeneration of a preexisting nodule, may become hemorrhagic spontaneously

clinical findings of a cysts are

palpable mass or neck swelling. accounts for the majority of “cold nodules” on nuc med scans

Thyroid adenoma

benign solid neoplastic growth

slow growing

complete fibrous encapsulation

thyroid adenoma appearance on ultrasound

may appear solid but also cystic due to degeneration

most are solitary but may develop as multinodular process

most are well circumscribed; circular or oval

thyroid adenoma commonly have

peripheral halos or calcification along the rim

thyroid carcinoma

rare, solitary nodule may be malignant in small percentages of cases, but risk of malignancy decrease with presence of multiple nodules

types of thyroid carcinoma

papillary, follicular, medullary, anaplastic

thyroid carcinoma signs and symptoms

lump in the neck which feels like hard mass on palpation, history of enlarging goiter, hoarseness, pressure symptoms

thyroid carcinoma has a

highly variable appearance, and depends on which type. calcifications are present in 50-80%. increased vascularity

Papillary carcinoma

most common type of thyroid carcinoma, least agrressive

major route of spread is through lymphatics to nearby cervical lymph nodes.

papillary carcinoma ultrasound appearance

usually hypoechoic and microcalcifications/hypervascularity are present.

follicular carcinoma

second most common type of carcinoma. spreads via the blood stream, usually solitary mass

2 types of follicular carcinoma

minimally invasive: well-encapsulated, focal invasion of capsular blood vessels of fibrous

widely invasive: not encapsulated, invasion of blood vessels and adjacent tissue occurs

follicular carcinoma appearance on ultrasound

irregular margins, thick irregular “halo”, nodular enlargement, tortuous internal blood vessels.

Follicular adenomas and follicular carcinoma’s cant be

distinguished on sonography of FNA. MUST USE HISTOLOGY

medullary carcinoma

rare, neuroendocrine neoplasm that secretes calcitonin.

aggressive

medullary carcinoma appearance

usually hypoechoic solid mass. calcium deposits and microcalcifications are noticed. coarse califications too.

anaplastic carcinoma

rare, highly aggressive, rapid growth. presents as a hard fixed mass. no effective therapy

anaplastic carcinoma ultrasound apperance

large, solid, hypoechoic mass, invasion of surrounding muscles and vessels of the neck

lymphoma

uncommon, primarily the non-hodgkin’s type

symptoms are airway obstruction

usually have hasimotos already

lymphoma ultrasound apperance

large, solid, hypoechoic, lobulated mass

color doppler typically hypovascular/nonvascular.

may compress or infiltrate adjacent thyroid parenchyma.

thyroiditis

swelling and tenderness of the thyroid gland.

caused by infection leading to massive infiltration of lymphocytes into the gland. also can be related to autoimmune disturbances

signs and symptoms of thyroiditis

diffusely enlarged, soft, palpable thyroid, hoarseness, neck swelling, decreased T3 and T4 in 50% cases

thyroiditis ultrasound appearance

diffusely enlarged gland, slightly irregular echo pattern, calcifications may occur after inflammation

subacute thyroiditis

granulomatous, diffuse inflammation following viral infection, benign, occurs transiently, gradual or fairly onset, may have severe pain

subacute thyroiditis signs and symptoms

enlarged, tender thyroid gland, painful swelling, fever, normal WBC count

subacute thyroiditis appearance on ultrasound

may be asymmetric, hypoechoic, discrete areas of increased and decreased echogenicity

Chronic (Reidel’s) thyroiditis

chronic, fibrotic inflammatory process

results in replacement of thyroid tissue with fibrotic tissue and scarring

rare; least common inflammatory process

signs and symptoms of chronic thyroiditis

insidious onset, patients present with pressure from adherence of the gland to the trachea and subcutaneous neck tissue

chronic thyroiditis ultrasound apperance

diffuse enlargement of both lobes and isthmus, heterogeneous echo pattern compared to that of normal gland due to fibrosis and scarring

hashimotos

chronic, progressive, destructive autoimmune disorder leading to chronic inflammation of thyroid

most common form of thyroiditis

signs and symptoms of hashimotos disease

painless, diffusely enlarged gland, mild to moderate tenderness, more common in young-middle aged females

ultrasound apperance of hashimotos

diffuse coarse parenchymal texture that is slightly more hypoechoic than normal thyroid.

ill-defined hypoechoic areas separated by thickened fibrous strands

eventually gland becomes severely damaged

homogenous enlargement initially, then heterogenous

graves disease

thyroid hyperfunction related to production of autoimmune antibodies directed against thyroid

characterized by thyrotoxicosis and is most common cause of hyperthyroidism

causes diffuse cellular hyperplasia

graves disease symptoms

hypermetabolism, increased t3 and t4, cutaneous manifestations, diffuse toxic goiter, protruding of the eyes

ultrasound of graves disease apperance

diffuse enlargement of gland with homogeneous texture, usually hypoechoic, low impedance vascularity

TI-RADS

Thyroid Imaging Reporting And Data System

helps avoid unnecessary cost and patient discomfort

fine needle aspiration (FNA)

ultrasound guided. fine needle attached to syringe

specimens obtained by the capillary action technique which is an up and down motion

core biopsy

ultrasound guided, preserves spatial arrangement of cells. tissue samples obtained using an automated hollow core needle. loud