The Thyroid and Parathyroid


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The Thyroid and Parathyroid

  2. 2. <ul><ul><ul><ul><li>Introduction/General Information </li></ul></ul></ul></ul><ul><li>A. Thyroid </li></ul><ul><li>1. Endocrine gland </li></ul><ul><li>a. Lobes are cone shaped </li></ul><ul><li>b. Apex extends to oblique line of thyroid cartilage </li></ul><ul><li>2. Highly vascular </li></ul>
  3. 3. 3. Anterior & lateral to larynx, trachea 4. Lobes connected by an isthmus 5. Pyramidal lobe may be present 6. Normally not palpable Thyroid, General Information, continued …
  4. 4. The Thyroid Gland <ul><li>Located in the anterior region of the neck </li></ul><ul><li>This gland has an accessory (pyramidal) lobe </li></ul>
  5. 5. Thyroid Gland, Anterior and Posterior Views <ul><li>Thyroid Gland: anterior view (left); and posterior view (right) </li></ul>
  6. 6. Thyroid, General Information, continued … 8. Isthmus crosses tracheal cartilages 2-4 9. Base located ~4-5 th tracheal cartilage 10. Thyroxin function: regulates basic metabolism in all cells
  7. 7. <ul><li>Thyroid, General Information, continued </li></ul><ul><ul><li>B. Parathyroid glands </li></ul></ul><ul><li>1. Usually four – two on each side (2-8 is normal) </li></ul><ul><li>2. Lie on the posterior surface of thyroid </li></ul><ul><li>3. May be embedded within thyroid gland </li></ul><ul><li>4. Regulate calcium/phosphate levels </li></ul><ul><li>5. Required for life </li></ul>
  8. 8. Parathyroid Glands (Post. view of thyroid) <ul><li>Parathyroid Glands are located on the posterior aspect of the thyroid; sometimes the tissue is embedded within thyroid tissue. </li></ul>
  9. 9. <ul><ul><ul><li>II. Detailed Anatomy </li></ul></ul></ul><ul><li>A. Thyroid </li></ul><ul><li>1. Largest endocrine gland in adult </li></ul><ul><li>2. Normally extends from ~ C-5 through ~ T-1 </li></ul><ul><li>3. Highly vascular </li></ul><ul><li>4. Weights ~20 - 30 grams </li></ul>
  10. 10. Thyroid, Detailed Anatomy, continued … 5. Pyramidal lobe a. present in ~ 33% of population. b. Extends upward from isthmus c. anterior to thyroid cartilage
  11. 11. 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. 12. Pyramidal Lobe of the Thyroid Gland Pyramidal Lobe Thyroid Gland, Anterior View
  13. 13. Thyroid, Detailed Anatomy, continued … c. Lobes: 1. Attached to cricoid cartilage by ligaments 2. Medial surface adapted to larynx and trachea
  14. 14. Thyroid, Detailed Anatomy, cont … 3. Lobes related posteriorly to the esophagus 4. Posterolateral surface a. related to carotid sheath b. overlaps carotid artery
  15. 15. Thyroid, Detailed Anatomy, con’t… d. Isthmus 1. 1.25 cm x 1.25 cm 2. Crosses @ tracheal rings ~2-4 3. Occasionally absent
  16. 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. 17. 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. 18. 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. 19. 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. 20. Thyroid gland, continued … 9. Autonomic innervation via a. Cervical portion of sympathetic trunk b. Parasympathetic fibers arise from Vagus X
  21. 21. 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. 22. Detailed Anatomy, continued … c. Damaging nerves results in partial or total paralysis of larynx d. Bordered by neurovascular structures contained in carotid sheath
  23. 23. 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. 24. Pretracheal fascia, continued … d. Fascia more dense anteriorly 1. Thyroid enlargement often occurs posteriorly 2. May compress trachea, esophagus 3. 1 st symptom may be hoarseness, difficulty swallowing
  25. 25. <ul><li>Parathyroid Gland, Detailed Anatomy </li></ul><ul><ul><li>B. Parathyroid glands </li></ul></ul><ul><ul><li>1. Yellow-brown </li></ul></ul><ul><ul><li>2. ovoid or lentiform structures </li></ul></ul><ul><ul><li>3. weigh ~ 50 mg each </li></ul></ul><ul><ul><li>4. Measure 3-10 mm x 2-6 mm x 1-4 mm </li></ul></ul>
  26. 26. <ul><li>Parathyroid Glands, con’t…. </li></ul><ul><li>5. Lie between posteromedial thyroid lobes and carotid sheath </li></ul><ul><ul><li>6. Close proximity to: </li></ul></ul><ul><ul><li>a. Tracheoesophageal groove </li></ul></ul><ul><ul><li>b. longus colli muscles </li></ul></ul>
  27. 27. 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. 28. <ul><ul><li>III. Thyroid/Parathyroid Diseases </li></ul></ul><ul><ul><li>A. Ultrasound useful in differentiating cystic from complex or solid masses </li></ul></ul><ul><ul><li>B. Thyroid Cysts </li></ul></ul><ul><ul><li>1. Typical cystic appearance </li></ul></ul><ul><ul><li>2. Colloid cysts </li></ul></ul><ul><ul><li>3. Thyroglossal duct cysts </li></ul></ul>
  29. 29. <ul><li>Pathology, cont… </li></ul><ul><ul><li>3. Branchial cleft cysts </li></ul></ul><ul><ul><li>a. More specific than pattern for other neoplasms </li></ul></ul><ul><ul><li>b. Are usually more cephalic </li></ul></ul><ul><ul><li>4. Only 20% of thyroid masses are simple cysts </li></ul></ul>
  30. 30. 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. 31. Transverse Section of Thyroid Gland Internal Jugular Vein Thyroid Gland, Left Lobe Trachea Esophagus Common Carotid Artery Sternocleidomastoid Muscle Brachial Plexus
  32. 32. 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. 33. 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. 34. 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. 35. <ul><ul><ul><li>IV. Thyroid Diseases </li></ul></ul></ul><ul><li>A. Metastasis from thyroid cancer </li></ul><ul><li>1. May invade local structures </li></ul><ul><li>a. trachea </li></ul><ul><li>b. esophagus </li></ul><ul><li>c. carotid artery </li></ul><ul><li>d. jugular vein </li></ul>
  36. 36. 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. 37. <ul><li>Thyroid Diseases, continued … </li></ul><ul><ul><li>B. Cystic Masses </li></ul></ul><ul><li>1. Colloid cyst: </li></ul><ul><li>a. Contains thyroglobulin </li></ul><ul><li>b. May have hemorrhagic center </li></ul><ul><li>c. May be aspirated </li></ul>
  38. 38. Thyroid Follicles showing Colloid Thyroid Follicles with colloid containing Thyroid hormones
  39. 39. Thyroid Diseases, continued … 2. Branchial cleft cyst a. Usually more cephalic b. Non-closure of a branchial cleft c. lie laterally
  40. 40. 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
  41. 41. 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. 42. 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. 43. 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. 44. <ul><li>Thyroid Diseases, continued … </li></ul><ul><ul><li>C. Complex/Solid Masses (Neoplasm) </li></ul></ul><ul><ul><li>1. Adenoma </li></ul></ul><ul><ul><li>a. Well-encapsulated </li></ul></ul><ul><ul><li>b. Usually solitary </li></ul></ul><ul><ul><li>c. Homogeneous </li></ul></ul>
  45. 45. <ul><li>Thyroid Diseases, Adenomas, continued … </li></ul><ul><ul><li>c. May be complex, with </li></ul></ul><ul><ul><li>1. sonolucent halo 2. echogenic center </li></ul></ul><ul><ul><li>d. 50% of thyroid cancers are papillary adenocarcinomas </li></ul></ul><ul><ul><li>2. Complex  solid masses show increased malignancy </li></ul></ul>
  46. 46. Adenoma of the Thyroid Gland <ul><li>Note atrophy of the left lobe with the tumor protruding from it </li></ul><ul><li>Right lobe may hypertrohy to compensate for loss of function in L. lobe </li></ul>
  47. 47. 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. 48. Goiter, continued … e. Nodules have variable echogenicity f. Treatable with iodine in diet g. More common inland, and before iodized salt
  49. 49. Types of Goiters <ul><li>Simple Goiter (L) and Nodular (Toxic) Goiter (R) </li></ul>
  50. 50. <ul><ul><li>D. Parathyroid Diseases </li></ul></ul><ul><li>1. Benign adenoma </li></ul><ul><li>a. Relatively common </li></ul><ul><li>b. usually results in hyperparathyroidism </li></ul><ul><li>2. Cancers are rare </li></ul><ul><li>3. Surgical excision gives > 90% cure rate </li></ul>
  51. 51. Parathyroid Diseases <ul><li>Pathogenesis of Hyperparathyroidism </li></ul><ul><ul><li>PTH increases blood calcium levels </li></ul></ul><ul><ul><li>Acts on bone, kidneys, small intestines </li></ul></ul>
  52. 52. Long-term Effects on the Skeletal System Hyperparathyroidism