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THYROID/PARATHYROID
I. Introduction/General Information
A. Thyroid
1. Endocrine gland
a. Lobes are cone shaped
b. Apex extends to oblique line
of thyroid cartilage
2. Highly vascular
Thyroid, General Information, continued …
3. Anterior & lateral to
larynx, trachea
4. Lobes connected by
an isthmus
5. Pyramidal lobe may
be present
6. Normally not
palpable
The Thyroid Gland
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Located in the
anterior region of
the neck
This gland has an
accessory
(pyramidal) lobe
Thyroid Gland, Anterior and Posterior Views
Thyroid Gland: anterior view (left); and posterior view (right)
Thyroid, General Information, continued …
8. Isthmus crosses tracheal
cartilages 2-4
9. Base located ~4-5th tracheal cartilage
10. Thyroxin function: regulates basic
metabolism in all cells
Thyroid, General Information, continued
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 gland
4. Regulate calcium/phosphate levels
5. Required for life
Parathyroid Glands (Post. view of thyroid)
Parathyroid Glands are located on the posterior aspect
of the thyroid; sometimes the tissue is embedded
within thyroid tissue.
II. Detailed Anatomy
A. Thyroid
1. Largest endocrine gland in adult
2. Normally extends from ~ C-5
through ~ T-1
3. Highly vascular
4. Weights ~20 - 30 grams
Thyroid, Detailed Anatomy, continued …
5. Pyramidal lobe
a. present in ~ 33% of population.
b. Extends upward from isthmus
c. anterior to thyroid cartilage
Thyroid, Detailed Anatomy, continued …
d. Embryologic remnant of
thyroglossal duct
e. formerly connected cecum of
tongue to thyroid diverticulum
f. Site of developing gland
Pyramidal Lobe of the Thyroid Gland
Pyramidal Lobe
Thyroid Gland, Anterior View
Thyroid, Detailed Anatomy, continued …
c. Lobes:
1. Attached to cricoid cartilage
by ligaments
2. Medial surface adapted to
larynx and trachea
Thyroid, Detailed Anatomy, cont …
3. Lobes related posteriorly to the
esophagus
4. Posterolateral surface
a. related to carotid sheath
b. overlaps carotid artery
Thyroid, Detailed Anatomy, con’t…
d. Isthmus
1. 1.25 cm x 1.25 cm
2. Crosses @
tracheal rings ~2-4
3. Occasionally
absent
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
Thyroid gland vascular, continued …
7. Drained by R & L superior,
middle and inferior thyroid veins
a. Veins arise from plexus
b. on anterior surface of gland
c. Extend over anterior surface
of trachea
Inferior
Thyroid
Vein
Thyroid gland, continued …
d. Lymph vessels
1. In interlobular connective
tissue between lobes
2. Connect with network in wall of
gland
3. terminate in thoracic and
right lymphatic ducts
Thyroid gland, continued …
8. Muscular landmarks
a. Sternocleidomastoid
muscles lie laterally
b. Longus colli (prevertebral)
muscles lie posteriorly
c. “Strap” muscles lie
anteriorly
Strap Muscles
Thyroid gland, continued …
9. Autonomic innervation via
a. Cervical portion of sympathetic
trunk
b. Parasympathetic fibers arise from
Vagus X
Detailed Anatomy, continued …
9.
Treatment considerations
a. Superior thyroid artery is
accompanied by superior
laryngeal nerve
b. Inferior thyroid artery is
accompanied by recurrent
laryngeal nerve
Detailed Anatomy, continued …
c. Damaging nerves
results in partial or total
paralysis of larynx
d. Bordered by
neurovascular
structures contained in
carotid sheath
Thyroid gland, continued …
11. Pretracheal fascia:
a. surrounds thyroid
b. Extends from hyoid bone to
fibrous pericardium
c. Encloses trachea, larynx,
pharynx, thyroid
d. Parathyroids and venous
plexus lie between layers
Pretracheal fascia, continued …
d. Fascia more dense anteriorly
1. Thyroid enlargement often
occurs posteriorly
2. May compress trachea,
esophagus
3. 1st symptom may be
hoarseness, difficulty
swallowing
Parathyroid Gland, Detailed Anatomy
B. Parathyroid glands
1. Yellow-brown
2. ovoid or lentiform structures
3. weigh ~ 50 mg each
4. Measure 3-10 mm x 2-6 mm x 1-4 mm
Parathyroid Glands, con’t….
5. Lie between posteromedial
thyroid lobes and carotid sheath
6. Close proximity to:
a. Tracheoesophageal groove
b. longus colli muscles
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
III. Thyroid/Parathyroid Diseases
A.
B.
Ultrasound useful in differentiating
cystic from complex or solid masses
Thyroid Cysts
1. Typical cystic appearance
2. Colloid cysts
3. Thyroglossal duct cysts
Pathology, cont…
3. Branchial cleft cysts
a. More specific than pattern
for other neoplasms
b. Are usually more cephalic
4. Only 20% of thyroid masses are
simple cysts
Pathology, cont…
C. Structures of Carotid Sheath
1. Jugular vein, carotid artery
2. Delineate lateral aspect of thyroid
3. Jugular vein lateral to carotid artery
a. vein has greater diameter
b. Is distensible on valsalva
maneuver
Transverse Section of Thyroid Gland
Trachea
Sternocleidomastoid Muscle
Thyroid Gland, Left Lobe
Internal Jugular Vein
Common Carotid Artery
Brachial Plexus
Esophagus
Gray-Scale anatomy, continued
D. Thyroid is more homogeneous and
echogenic than surrounding muscle
1. Sternocleidomastoid (lateral)
2. Longus colli (posterior)
E. US is less helpful w/ complex masses
or diffuse parenchymal disorders
Gray-Scale Anatomy, continued …
F. Parathyroids are difficult to see
1. Size and location are variable
2. Usually:
a. moderately echogenic
b.
c.
d.
e.
well-circumscribed
capsule around
anterior to longus colli
medial to common carotid a.
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
IV. Thyroid Diseases
A. Metastasis from thyroid cancer
1. May invade local structures
a. trachea
b. esophagus
c. carotid artery
d. jugular vein
Thyroid Diseases, con’t…
2. Innervation may be involved
a. Voice, speech changes
b. Horner’s Syndrome of eye
1. droopy eye
2. dryness
3. small pupil
Thyroid Diseases, continued …
B. Cystic Masses
1. Colloid cyst:
a. Contains thyroglobulin
b. May have hemorrhagic center
c. May be aspirated
Thyroid Follicles showing Colloid
Thyroid Follicles
with colloid
containing Thyroid
hormones
Thyroid Diseases, continued …
2. Branchial cleft cyst
a. Usually more cephalic
b. Non-closure of a branchial
cleft
c. lie laterally
Thyroid Diseases, continued …
3. Thyroglossal Duct Cyst
a. Lies @ midline
b. Represents non-closure of
thryoglossal duct
c. Congenital anomaly:
1. retention of tract
2. between thyroid and
foramen cecum
Thyroglossal Duct Cyst, Thyroid Disease, continued …
d. Usually surrounded by hyoid
bone
e. More frequently diagnosed in
pediatric age groups
f. may be asymptomatic
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
Thyroid, continued …
i. Treatment:
1. excision of cyst & central
hyoid bone
2. < 1% accompanied by
cancer
j.
Account for ~ 70% of
congenital cysts of neck
k. may appear at any location
along duct
Thyroid Diseases, continued …
C. Complex/Solid Masses (Neoplasm)
1. Adenoma
a. Well-encapsulated
b. Usually solitary
c. Homogeneous
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
Adenoma of the Thyroid Gland
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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
Thyroid, continued …
3. Goiter
a. Enlargement of thyroid gland
b. due to insufficient iodine
c. Gland appears nodular with
irregular outline
d. Grossly enlarged
Goiter, continued …
e. Nodules have variable
echogenicity
f. Treatable with iodine in diet
g. More common inland, and
before iodized salt
Types of Goiters
Simple Goiter (L) and Nodular (Toxic) Goiter (R)
D. Parathyroid Diseases
1. Benign adenoma
a. Relatively common
b. usually results in
hyperparathyroidism
2. Cancers are rare
3. Surgical excision gives > 90%
cure rate
Parathyroid Diseases
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Pathogenesis of
Hyperparathyroidism
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PTH increases blood
calcium levels
Acts on bone,
kidneys, small
intestines
Hyperparathyroidism
Long-term Effects on the Skeletal System