Thyroid and Parathyroid 2

8/14/2019 Thyroid and Parathyroid 2

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THYROID/PARATHYROID


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Thyroid gland,

1. 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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Investing layer of DCF

Pretracheal fascia


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Investing layer of deep cervical fascia

Pretracheal layer

of dcf

Muscular portion of

pretracheal layer of DCF


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Thyroid gland

Surrounded by thin fibrous capsule of

connective tissue

External to this is pretracheal fascia

derived from deep cervical fascia

Attached to cricoid and thyroid cartilages

Thus, moves up and down with larynx

during swallowing


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Investinglayer

scm

sternothyroid

sternohyoid

omohyoid


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sternohyoid

sternothyroid

omohyoid


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I. Introduction/General Information

A. 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 to

larynx, trachea

4. Lobes connected byan isthmus

5. Pyramidal lobe may

be present

6. Normally notpalpable

Thyroid, General Information, continued


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The Thyroid Gland

Located in the

anterior region of the

neck


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Thyroid Gland, Anterior and Posterior Views

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


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Thyroid, General Information, continued

8. Isthmus crosses tracheal

cartilages 2-4

9. Base located ~4-6th tracheal cartilage

10. Thyroxin function: regulates basicmetabolism in all cells


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II. Detailed Anatomy

A. Thyroid

1. Largest endocrine gland

2. Extends fr C-5 to T-1

3. Highly vascular4. Weighs ~20 - 30 grams


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Thyroid gland

Clasps the pharynx,

larynx, esophagus andtrachea like a shield

Lies deep to

sternothyroid and

sternohyoid

Each lobe [5cm]

extends to level of 6th

tracheal cartilage


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Thyroid gland

Size varies greatly

Larger in women

Enlarges dur pregnancy May enlarge slightly dur menstruation


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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 of

thyroglossal 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 cartilage

by 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, Detailed Anatomy, cont

d. Isthmus

1. 1.25 cm x 1.25 cm

2. Crosses @

tracheal rings ~2-4

3. Rarely absent


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Thyroid gland vascular, continued

6. Highly vascular gland supplied by four large arteries

a. R & L inferior thyroid artery

b. R & L superior thyroid artery


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BLOOD SUPPLY (THYROID GLAND) Superior thyroid artery

1st anterior branch of

External Carotid Art Descends the lateral part of

the neck under the superiorbelly of omohyoid andsternothyroid muscles

Above the level of thesuperior pole, accompaniedby the external laryngealbranch of the superiorlaryngeal nerve


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BLOOD SUPPLY (THYROID GLAND) Nerve parallels artery until

it reaches the superior

lobe where it coursesunder the sternothyroid toinsert in the cricothyroidmuscle

High ligation of STA mayaffect nerve

Dysphonia, denervatesCT muscle (regulation of

pitch) No sensation to mucosa

of pyriform sinus andfalse vocal cords


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BLOOD SUPPLY (THYROID GLAND)

Inferior thyroid artery

Arises from the thyrocervicaltrunk

Branch of 1st part ofsubclavian artery level of the1st rib

Ascends vertically for a shortdistance before turningmedially, forming an archingloop and entering thetracheoesophageal groove


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Most of branches penetrate posterior

aspect of lateral lobe

Anastomoses with STA near the superior

pole

Small vessels intermingle with recurrent

laryngeal nerve


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Thyroid gland vascular, continued

Venous drainage

a. Superior thyroid vein int jugular vein [ IJV ]

b. Middle thyroid vein IJV

c. Inferior thyroid veinbrachiocephalic vein

InferiorThyroid

Vein


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2 pairs of arteries Superior thyroid a

Inferior thyroid a

3 pairs of veins Superior thyroid v

Middle thyroid v

Inferior thyroid v


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Sup thyroid art and vein

Middle thyroid

vein

Inf thyroid vein

Inf thyroid artery


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Thyroid gland, continued

Lymph vessels

1. In interlobular connectivetissue between lobes

2. Connect with network in wall of

gland

3. terminate in thoracic andright lymphatic ducts


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Surgical Anatomy:

Lymphatics


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Thyroid gland, continued

Muscular landmarks

a. Sternocleidomastoidmuscles lie laterally

b. Longus colli (prevertebral)

muscles lie posteriorly

c. Strap muscles lie

anteriorly

Strap Muscles


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INNERVATION (THYROID GLAND)

Autonomic nervous

system

Parasympathetic

fibers ~ vagus nerve Sympathetic fibers ~

superior, middle,

inferior sympathetic

ganglia of the

sympathetic trunk


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Sympathetic trunk

Recurrnt laryngealnerve [Vagus]


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Detailed Anatomy, continued

Treatment considerations

a. Superior thyroid artery is

accompanied by superior

laryngeal 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

SLN injury unable to

reach high pirch

RLN injury VC

paralysis, hoarse voice


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II. Parathyroid glands

1. Usually four two on each side

(2 to 8 is normal)2. Posterior surface of thyroid

3. Embedded w/in thyroid gland

4. 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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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 posteromedial

thyroid 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 between

trachea and thyroid

9. Blood, lymphatic and nerve supply:

same as for thyroid

P th id Gl d A t


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Parathyroid Gland Anatomy

Four Parathyroid

glands are usually

found posterior to

the thyroid gland

Weight =50mg each Parathyroid hormone

(PTH) is made by

these glands


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PARATHYROID GLAND

Superior pair ~ posterior aspect of the

superior pole of the lateral lobes of the

thyroid gland and close to the recurrent

laryngeal nerve (constant location)


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ANATOMY (PARATHYROID GLAND)

Inferior pair ~ posterior aspect of theinferior pole of the lateral lobes of thethyroid gland

Pathologic enlargements of the inferiorPTG may extend to the trachea andesophagus

Maintain serum calcium and phosphoruslevels


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Parathyroid g


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34F w/ anterior neck mass


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34F w/ anterior neck mass


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III. Thyroid/Parathyroid DiseasesA. Ultrasound useful in differentiating

cystic from complex or solid masses

B. Thyroid Cysts1. Typical cystic appearance

2. Colloid cysts

3. Thyroglossal duct cysts


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Pathology, cont

3. Thyroid scan

Warm, hot or cold nodule

4. Only 20% of thyroid masses are

simple cysts


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END

Lab on Monday

Radioanatomy lec on Tue/Thurs

Lab again on Friday

Exam on Jan 22


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Pathology, cont

C. Structures of Carotid Sheath

1. Jugular vein, carotid artery2. Delineate lateral aspect of thyroid

3. 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 around

d. anterior to longus colli

e. 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. trachea

b. esophagus

c. carotid artery

d. 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 colloid

containing Thyroid

hormones


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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 hyoid

bone

e. More frequently diagnosed in

pediatric age groups

f. may be asymptomatic


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Thyroid, continued

g. Incidence in patients undergoing

thyroid surgery:

1. 4% have this cyst

2. 28% of those with the cyst

are > 50 years old

h. Symptoms: painless swelling at

midline of neck


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Thyroid, continued

i. Treatment:

1. excision of cyst & central

hyoid bone2. < 1% accompanied by

cancer

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 adenocarcinomas

2. Complex solid masses show

increased malignancy

Ad f th Th id Gl d


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Adenoma of the Thyroid Gland

Note atrophy of the left

lobe with the tumor

protruding from it Right lobe may

hypertrohy to

compensate 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 variable

echogenicity

f. Treatable with iodine in diet

g. More common inland, andbefore iodized salt

T f G it


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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

P th id Di


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Parathyroid Diseases

Pathogenesis of

Hyperparathyroidism

PTH increases blood

calcium levels

Acts on bone,

kidneys, small

intestines


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Long-term Effects on the Skeletal System

Hyperparathyroidism

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Thyroid and Parathyroid 2