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THYROID/PARATHYROID

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.

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THYROID/PARATHYROID

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  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. 3. Anterior & lateral to larynx, trachea4. Lobes connected by an isthmus5. Pyramidal lobe may be present6. Normally not palpable Thyroid, General Information, continued …

  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. 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. 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-5 through ~ T-1 • 3. Highly vascular • 4. Weights ~20 - 30 grams

  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. 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 Pyramidal Lobe Thyroid Gland, Anterior View

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

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

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

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

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

  45. 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

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

  49. 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

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