biol226lec08 thyroid parathyroid glands

7/31/2019 BIOL226Lec08 Thyroid Parathyroid Glands

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I. Introduction/General InformationA. Thyroid

1. Endocrine glanda. Lobes are cone shaped

b. Apex extends to oblique line

of thyroid cartilage

2. Highly vascular


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3. Anterior & lateral tolarynx, trachea

4. Lobes connected byan isthmus

5. Pyramidal lobe maybe present

6. Normally notpalpable

Thyroid, General Information, continued


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The Thyroid Gland

Located in theanterior region of

the neck This gland has an

accessory(pyramidal) lobe


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Thyroid Gland, Anterior and Posterior Views

Thyroid Gland: anterior view (left); and posterior view (right)


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8. Isthmus crosses trachealcartilages 2-4

9. Base located ~4-5th tracheal cartilage

10. Thyroxin function: regulates basicmetabolism in all cells


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B. Parathyroid glands

1. Usually four two on each side(2-8 is normal)

2. Lie on the posterior surface of thyroid

3. May be embedded within thyroid gland4. Regulate calcium/phosphate levels5. Required for life


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Parathyroid Glands (Post. view of thyroid)

Parathyroid Glands are located on the posterior aspectof the thyroid; sometimes the tissue is embeddedwithin thyroid tissue.


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II. Detailed Anatomy

A. Thyroid

1. Largest endocrine gland in adult2. Normally extends from ~ C-5

through ~ T-1

3. Highly vascular

4. Weights ~20 - 30 grams


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Thyroid, Detailed Anatomy, continued

5. Pyramidal lobe

a. present in ~ 33% of population.

b. Extends upward from isthmus

c. anterior to thyroid cartilage


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d. Embryologic remnant ofthyroglossal duct

e. formerly connected cecum of

tongue to thyroid diverticulumf. Site of developing gland


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Pyramidal Lobe of the Thyroid Gland

Pyramidal Lobe

Thyroid Gland, Anterior View


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c. Lobes:

1. Attached to cricoid cartilageby ligaments

2. Medial surface adapted tolarynx and trachea


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Thyroid, Detailed Anatomy, cont

3. Lobes related posteriorly to the

esophagus4. Posterolateral surface

a. related to carotid sheath

b. overlaps carotid artery


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Thyroid gland vascular, continued

6. Highly vascular gland supplied by four large arteriesa. R & L inferior thyroid artery

b. R & L superior thyroid artery


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Thyroid gland vascular, continued

7. Drained by R & L superior,

middle and inferior thyroid veinsa. Veins arise from plexus

b. on anterior surface of glandc. Extend over anterior surface

of trachea

InferiorThyroidVein


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Thyroid gland, continued

d. Lymph vessels

1. In interlobular connectivetissue between lobes

2. Connect with network in wall ofgland

3. terminate in thoracic andright lymphatic ducts


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8. Muscular landmarks

a. Sternocleidomastoidmuscles lie laterally

b. Longus colli (prevertebral)muscles lie posteriorly

c. Strap muscles lie

anteriorly

Strap Muscles


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Detailed Anatomy, continued

9. Treatment considerations

a. Superior thyroid artery is

accompanied by superiorlaryngeal nerve

b. Inferior thyroid artery is

accompanied by recurrentlaryngeal nerve


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Detailed Anatomy, continued

c. Damaging nerves

results in partial or totalparalysis of larynx

d. Bordered byneurovascular

structures contained incarotid sheath


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11. Pretracheal fascia:a. surrounds thyroid

b. Extends from hyoid bone tofibrous pericardium

c. Encloses trachea, larynx,pharynx, thyroid

d. Parathyroids and venousplexus lie between layers


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Pretracheal fascia, continued

d. Fascia more dense anteriorly1. Thyroid enlargement often

occurs posteriorly2. May compress trachea,

esophagus3. 1st symptom may be

hoarseness, difficultyswallowing


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Parathyroid Gland, Detailed Anatomy

B. Parathyroid glands

1. Yellow-brown2. ovoid or lentiform structures

3. weigh ~ 50 mg each

4. Measure 3-10 mm x 2-6 mm x 1-4 mm


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Parathyroid Glands, cont.

5. Lie between posteromedialthyroid lobes and carotid sheath

6. Close proximity to:

a. Tracheoesophageal groove

b. longus colli muscles


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Parathyroid Glands, continued

7. Position of superior glands is more

predictable

8. Aberrant glands may lie betweentrachea and thyroid

9. Blood, lymphatic and nerve supply:same as for thyroid


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Pathology, cont

3. Branchial cleft cysts

a. More specific than patternfor other neoplasms

b. Are usually more cephalic

4. Only 20% of thyroid masses aresimple cysts


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Pathology, cont

C. Structures of Carotid Sheath

1. Jugular vein, carotid artery2. Delineate lateral aspect of thyroid3. Jugular vein lateral to carotid artery

a. vein has greater diameterb. Is distensible on valsalva

maneuver


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Transverse Section of Thyroid Gland

Internal Jugular Vein

Thyroid Gland, Left Lobe

Trachea

Esophagus

Common Carotid Artery

Sternocleidomastoid Muscle

Brachial Plexus


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Gray-Scale anatomy, continued

D. Thyroid is more homogeneous and

echogenic than surrounding muscle1. Sternocleidomastoid (lateral)2. Longus colli (posterior)

E. US is less helpful w/ complex massesor diffuse parenchymal disorders


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Gray-Scale Anatomy, continued

F. Parathyroids are difficult to see

1. Size and location are variable

2. Usually:

a. moderately echogenic

b. well-circumscribedc. capsule aroundd. anterior to longus collie. medial to common carotid a.


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Parathyroids, continued

3. Longus Colli (prevertebral) Muscles

a. Attachments:

1. O = cervical vertebrae

2. I = cervical vertebrae

b. Action: twists, bends neck

c. Lie posterior


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IV. Thyroid Diseases

A. Metastasis from thyroid cancer

1. May invade local structuresa. tracheab. esophagusc. carotid arteryd. jugular vein


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Thyroid Diseases, cont

2. Innervation may be involved

a. Voice, speech changes

b. Horners Syndrome of eye

1. droopy eye

2. dryness3. small pupil


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Thyroid Diseases, continued

B. Cystic Masses

1. Colloid cyst:

a. Contains thyroglobulin

b. May have hemorrhagic center

c. May be aspirated


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Thyroid Follicles showing Colloid

Thyroid Follicleswith colloidcontaining Thyroidhormones


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2. Branchial cleft cyst

a. Usually more cephalic

b. Non-closure of a branchial

cleft

c. lie laterally


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3. Thyroglossal Duct Cyst

a. Lies @ midline

b. Represents non-closure ofthryoglossal duct

c. Congenital anomaly:

1. retention of tract

2. between thyroid and

foramen cecum


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Thyroglossal Duct Cyst, Thyroid Disease, continued

d. Usually surrounded by hyoidbone

e. More frequently diagnosed in

pediatric age groupsf. may be asymptomatic


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Thyroid, continued

g. Incidence in patients undergoingthyroid surgery:

1. 4% have this cyst

2. 28% of those with the cystare > 50 years old

h. Symptoms: painless swelling atmidline of neck


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Thyroid, continued

i. Treatment:

1. excision of cyst & central

hyoid bone

2. < 1% accompanied bycancer

j. Account for ~ 70% ofcongenital cysts of neck

k. may appear at any location

along duct


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C. Complex/Solid Masses (Neoplasm)

1. Adenoma

a. Well-encapsulated

b. Usually solitary

c. Homogeneous


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Thyroid Diseases, Adenomas, continued

c. May be complex, with

1. sonolucent halo

2. echogenic center

d. 50% of thyroid cancers are

papillary adenocarcinomas2. Complex solid masses show

increased malignancy


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Adenoma of the Thyroid Gland

Note atrophy of the leftlobe with the tumor

protruding from it Right lobe may

hypertrohy tocompensate for loss of

function in L. lobe


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Thyroid, continued

3. Goiter

a. Enlargement of thyroid gland

b. due to insufficient iodine

c. Gland appears nodular with

irregular outline

d. Grossly enlarged


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Goiter, continued

e. Nodules have variableechogenicity

f. Treatable with iodine in diet

g. More common inland, andbefore iodized salt


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Types of Goiters

Simple Goiter (L) and Nodular (Toxic) Goiter (R)


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D. Parathyroid Diseases1. Benign adenoma

a. Relatively common

b. usually results inhyperparathyroidism

2. Cancers are rare

3. Surgical excision gives > 90%cure rate


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Parathyroid Diseases

Pathogenesis ofHyperparathyroidism

PTH increases bloodcalcium levels

Acts on bone,kidneys, smallintestines


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Long-term Effects on the Skeletal System

Hyperparathyroidism

biol226lec08 thyroid parathyroid glands

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