THYROID/PARATHYROID

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 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)

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

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

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

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

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

Pyramidal Lobe of the Thyroid Gland Thyroid Gland, Anterior View

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

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

1. 1.25 cm x 1.25 cm d. Isthmus 2. Crosses @ tracheal rings ~2-4 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

Thyroid Follicles showing Colloid Thyroid Follicles with colloid containing Thyroid hormones

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

b. Represents non-closure of thryoglossal duct c. Congenital anomaly: 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

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

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

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

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

1. sonolucent halo 2. echogenic center 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 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

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

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

Simple Goiter (L) and Nodular (Toxic) Goiter (R) 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 Pathogenesis of Hyperparathyroidism PTH increases blood calcium levels Acts on bone, kidneys, small intestines

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