1. THYROID/PARATHYROID

2. 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

3. 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

4. The Thyroid Gland
Located in the anterior region of the neck
This gland has an accessory (pyramidal) lobe

5. Thyroid Gland, Anterior and Posterior Views
Thyroid Gland: anterior view (left); and posterior view (right)

6. 8. Isthmus crosses tracheal cartilages 2-4
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

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

8. 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.

9. II. Detailed Anatomy
A. Thyroid
1. Largest endocrine gland in adult
2. Normally extends from ~ C through ~ T-1
3. Highly vascular
4. Weights ~ grams

10. a. present in ~ 33% of population. b. Extends upward from isthmus
Thyroid, Detailed Anatomy, continued …
5. Pyramidal lobe
a. present in ~ 33% of population.
b. Extends upward from isthmus
c. anterior to thyroid cartilage

11. d. Embryologic remnant of thyroglossal duct
Thyroid, Detailed Anatomy, continued …
d. Embryologic remnant of thyroglossal duct
e. formerly connected cecum of tongue to thyroid diverticulum
f. Site of developing gland

12. Pyramidal Lobe of the Thyroid Gland
Thyroid Gland, Anterior View

13. 1. Attached to cricoid cartilage by ligaments
Thyroid, Detailed Anatomy, continued …
c. Lobes:
1. Attached to cricoid cartilage by ligaments
2. Medial surface adapted to larynx and trachea

14. 3. Lobes related posteriorly to the esophagus
Thyroid, Detailed Anatomy, cont …
3. Lobes related posteriorly to the esophagus
4. Posterolateral surface
a. related to carotid sheath
b. overlaps carotid artery

15. 1. 1.25 cm x 1.25 cm d. Isthmus 2. Crosses @ tracheal rings ~2-4
Thyroid, Detailed Anatomy, con’t…
d. Isthmus
cm x 1.25 cm
2. tracheal rings ~2-4
3. Occasionally absent

16. 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

17. 7. Drained by R & L superior, middle and inferior thyroid veins
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

18. 1. In interlobular connective tissue between lobes
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

19. a. Sternocleidomastoid muscles lie laterally
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

20. a. Cervical portion of sympathetic trunk
Thyroid gland, continued …
9. Autonomic innervation via
a. Cervical portion of sympathetic trunk
b. Parasympathetic fibers arise from Vagus X

21. 9. Treatment considerations
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

22. c. Damaging nerves results in partial or total paralysis of larynx
Detailed Anatomy, continued …
c. Damaging nerves results in partial or total paralysis of larynx
d. Bordered by neurovascular structures contained in carotid sheath

23. 11. Pretracheal fascia: a. surrounds thyroid
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

24. 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

25. 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

26. 5. Lie between posteromedial thyroid lobes and carotid sheath
Parathyroid Glands, con’t….
5. Lie between posteromedial thyroid lobes and carotid sheath
6. Close proximity to:
a. Tracheoesophageal groove
b. longus colli muscles

27. 7. Position of superior glands is more predictable
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

28. III. Thyroid/Parathyroid Diseases
A. Ultrasound useful in differentiating cystic from complex or solid masses
B. Thyroid Cysts
1. Typical cystic appearance
2. Colloid cysts
3. Thyroglossal duct cysts

29. a. More specific than pattern for other neoplasms
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

30. 1. Jugular vein, carotid artery 2. Delineate lateral aspect of thyroid
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

31. Transverse Section of Thyroid Gland
Trachea
Thyroid Gland, Left Lobe
Sternocleidomastoid Muscle
Internal Jugular Vein
Common Carotid Artery
Brachial Plexus
Esophagus

32. D. Thyroid is more homogeneous and echogenic than surrounding muscle
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

33. F. Parathyroids are difficult to see 1. Size and location are variable
Gray-Scale Anatomy, continued …
F. Parathyroids are difficult to see
1. Size and location are variable
2. Usually:
a. moderately echogenic b. well-circumscribed c. capsule around d. anterior to longus colli e. medial to common carotid a.

34. b. Action: twists, bends neck c. Lie posterior
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

35. IV. Thyroid Diseases
A. Metastasis from thyroid cancer
1. May invade local structures
a. trachea
b. esophagus
c. carotid artery
d. jugular vein

36. 2. Innervation may be involved a. Voice, speech changes
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

37. a. Contains thyroglobulin b. May have hemorrhagic center
Thyroid Diseases, continued …
B. Cystic Masses
1. Colloid cyst:
a. Contains thyroglobulin
b. May have hemorrhagic center
c. May be aspirated

38. Thyroid Follicles showing Colloid
Thyroid Follicles with colloid containing Thyroid hormones

39. a. Usually more cephalic b. Non-closure of a branchial cleft
Thyroid Diseases, continued …
2. Branchial cleft cyst
a. Usually more cephalic
b. Non-closure of a branchial cleft
c. lie laterally

40. b. Represents non-closure of thryoglossal duct c. Congenital anomaly:
Thyroid Diseases, continued …
3. Thyroglossal Duct Cyst
a. midline
b. Represents non-closure of thryoglossal duct
c. Congenital anomaly:
1. retention of tract
2. between thyroid and foramen cecum

41. d. Usually surrounded by hyoid bone
Thyroglossal Duct Cyst, Thyroid Disease, continued …
d. Usually surrounded by hyoid bone
e. More frequently diagnosed in pediatric age groups
f. may be asymptomatic

42. h. Symptoms: painless swelling at midline of neck
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

43. 1. excision of cyst & central hyoid bone
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

44. C. Complex/Solid Masses (Neoplasm) 1. Adenoma a. Well-encapsulated
Thyroid Diseases, continued …
C. Complex/Solid Masses (Neoplasm)
1. Adenoma
a. Well-encapsulated
b. Usually solitary
c. Homogeneous

45. 1. sonolucent halo 2. echogenic center
Thyroid Diseases, Adenomas, continued …
c. May be complex, with
1. sonolucent halo echogenic center
d. 50% of thyroid cancers are papillary adenocarcinomas
2. Complex  solid masses show increased malignancy

46. 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

47. a. Enlargement of thyroid gland b. due to insufficient iodine
Thyroid, continued …
3. Goiter
a. Enlargement of thyroid gland
b. due to insufficient iodine
c. Gland appears nodular with irregular outline
d. Grossly enlarged

48. e. Nodules have variable echogenicity
Goiter, continued …
e. Nodules have variable echogenicity
f. Treatable with iodine in diet
g. More common inland, and before iodized salt

49. Simple Goiter (L) and Nodular (Toxic) Goiter (R)
Types of Goiters
Simple Goiter (L) and Nodular (Toxic) Goiter (R)

50. 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

51. Parathyroid Diseases Pathogenesis of Hyperparathyroidism
PTH increases blood calcium levels
Acts on bone, kidneys, small intestines

52. Long-term Effects on the Skeletal System
Hyperparathyroidism
Long-term Effects on the Skeletal System