Thyroid and Parathyroid

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cxuofa
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64551
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Thyroid and Parathyroid
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2011-02-08 21:02:33
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thyroid parathyroid cancer
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thyroid, parathyroid, cancer
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  1. Embryology of the Thyroid gland
    • Originate from the primitive pharynx and neural cres
    • Forms from endodermal diverticulum of the floor of the primitive pharynx
    • Follicular elements of thyroid tissue develop during 2nd to 3rd week of fetal life
    • Proximal portion forms the foramen caecum
    • Distal/caudal segment descents into the neck
    • Thyroglossal duct tract is formed during this descent
  2. The ultimobranchial bodies are formed from
    • tissue from the neural crest and fused fourth and fifth branchial pouches
    • gives rise to parafollicular cells (c cells)
    • ultimobranchial body fuses with the thyroid gland
    • results in parafollicular cells being restricted to a zone within the middle to upper thirds of the thyroid gland
    • MTCs commonly arise from this region
  3. Inferior parathyroid glands arise from
    4th branchial pounches
  4. Pyramidal lobe of the thyroid gland arises from
    Caudal tract remnant of the thyroglossal duct
  5. Ectopic Thyroid tissue arises from
    Failure of migration or excessive descent
  6. Lingual thyroid arises from
    Complete arrest of the descent of the developing thyroid with resulting presence of thyroid tissue at the tongue base
  7. Lateral thyroid tissue arises from
    • Debate whether lateral neck thyroid tissue represents normal thyroid tissue versus metastatic thyroid carcinoma
    • treated as thyroid cancer with resection
  8. Features of Thyroglossal duct cyst
    • Most common congenital cervical anomaly
    • Cyst can be lined by stratified squamous or columnar epithelium
    • Can occur anywhere from the base of the tongue to the upper mediastinum
  9. Benign Thyroid Lesions
    • Thyroiditis
    • e.g. Hashimoto Thyroiditis and Riedel Thyroiditis
    • Adenomas
    • Goiters
  10. Types of Thyroiditis
    • Chronic lymphocytic Thyroiditis (Hashimoto Thyroiditis)
    • - antibodies to thyroid peroxidase and thyroglobulin
  11. Riedel Thyroiditis
    - rare disorder characterized by fibrosis of the thyroid gland
  12. Clinical Features of Hashimoto Thyroiditis
    immunologically mediated thyroid cell dmamage by autoantibodies against thyroid peroxidase and thyroglobulin and TSH receptor
  13. presents as an incidental asymptomatic goiter in middle-aged women
    • can occur at any age
    • most common cause of hypothyroidism
  14. Types of Thyroid adenomas
    • Follicular adenoma
    • Hurthle Cell adenoma
    • Hyalinizing trabecular adenoma
    • Nodular (adenomatous) goiter
  15. Malignant Lesions of the Thyroid include
    • Papillary carcinoma
    • Follicular carcinoma
    • Hurthle-cell Variant
    • Medullary thyroid carcinoma
    • Anaplastic thyroid carcinoma
  16. Gross Features of PTC
    • Ill-defined margins
    • Firm consistency
    • Whitish colour
    • Granular cut surface
  17. Histologic features of PTC
    • Papillae
    • Subtle irregularities in the nuclear contours
    • Pseudoinclusions with cytoplasmic invaginations
    • Psammoma bodies
  18. Histologic variants of PTC
    • Papillary thyroid microcarcinoma
    • Follicular variant
    • Encapsulated variant
    • Diffuse sclerosing variant
    • Oxyphilic cell variant
    • Tall-cell variant
    • Columnar cell variant
  19. Pathologic features of PTC
    • Multicentric involvement
    • Extrathyroidal extension is common
    • (muscle, RLN, and trachea)
    • Lymph node involvement in 30%
    • <5% have distant metastasis at time of diagnosis
  20. Risk factors of PTC
    • Previous ionizing radiation (e.g. head and neck irradiation for childhood lymphoma)
    • Syndromes involving familial PTC: Cowden syndrome
    • Family history
  21. What is Cowden syndrome
    Multiple hamartomas, breast tumours, and follicular/papillary thyroid tumours
  22. Clinical Features of Follicular thyroid carcinoma
    • 13% of all thryoid carcinomas
    • 10-year survival is 60%
    • 10 to 15% present with distant metastasis
    • Less nodal metastasis
  23. What is the 10-year survival of PTC
    96%
  24. Gross features of FTC
    • solitary tumours
    • thick fibrous capsule
    • hypercellualr
    • Frozen section is often not sufficient for diagnosis
    • FNA not helpful
  25. Variants of FTC
    • Minimally invasive
    • Widely invasive
  26. Risk factors for FTC
    • Radiation exposure
    • Chronic goiter secondary to hypothyroidism
  27. Hurthle Cell Carcinoma
    • Traditionally considered a subtype of FTC
    • 15% of FTCs
    • Histologically, oncocytes rich in mitochondria or Hurthle cells (large, polygonal, follicular cells containing dense eosinophilic cytoplasm, marked nuclear pleomorphism)
    • 2% of thyroid carcinomas
  28. Clinical Presentation of FTC
    • Presents with thyroid mass or nodule
    • 35% of patients develop distance metastasis at some point
  29. Features of Anaplastic Carcinoma
    • <5% of all thryoid malignancies
    • highly agressive
    • Invariably fatal
    • Mean survival from time of diagnosis is 3to 6 months
    • Predominantly occurs in older individuals (peak in 7th decade)
    • Sites of metastasis: lung, bone, brain, and intestine
  30. Clinical Presentation of Anaplastic Thyroid Carcinoma
    • Rapidly expanding neck mass or sudden changein size of preexisting goiter
    • May have associated symptoms of dysphagia, hoarseness, dyspnea, cough, pain
    • Horner's syndrome
  31. Gross and Histologic features of Anaplastic thyroid carcinoma
    • large, bulky infiltrative masses
    • gray-white
    • fibrous with areas of focal necrosis and hemorrage
  32. Histologic variants of ATC
    • Spindle cell
    • Giant cell
    • pleomorphic
    • Malignant fibrous
    • Histiocytic
    • Squamoid cell
  33. Lymphoma of the Thyroid
    • <5% of thyroid malignancies
    • Mean age of diagnosis of 60 - 65 yrs
    • Most common type: low to intermediate grade NHL from B-cells
    • Increased risk with Hashimoto thyroiditis
  34. Pitfalls of FNA
    • Cannot distinguish between benign microfollicular adenomas and differentiated FTCs
    • Cannot differentiate Hurthle cell lesion from Hashimoto thyroiditis
  35. Patterns of histologic appearance of follicular adenomas
    • trabecular
    • follicular
    • microfollicular
    • solid
  36. Thyroid FNA categories (Bethesda)
    • Risk of Malignancy
    • Benign <1%
    • Atypia of US 5 - 10%
    • Neoplasm 20 - 30%
    • Suspicious for Malignancy 50 - 75%
    • Malignant 100%
    • Non-diagnostic
  37. Epidemiology of Thyroid nodules
    • Palpable in 4 - 7% of adults (1% in males, 5% in females, increased with age)
    • Increases with age (esp. > 50)
    • Found incidentally in 10 - 31% of thyroid ultrasound (5% of these are malignant; upto 15% with high risk factors)
  38. Benefits of Thyroid FNA
    • High accuracy (90 - 100%)
    • False positive of <1%
    • False negative rates of 1 - 11%
    • Safe, inexpensive, easily performed, minimal patient discomfort
  39. Recommended follow-up depending on pathologic FNA findings:
    • Benign - periodic U/S
    • Atypia of unknown significance - Repeat FNA
    • Neoplasm - lobectomy/hemithyroidectomy
    • Suspicious for malignancy -
    • Malignant - proper staging, definitive surgery +/- RT
    • Non-diagnostic - repeat FNA
  40. Cystic Thyroid lesions
    • Low risk of malignancy if simple cysts (1 - 4%)
    • Higher risk if:
    • mixed cystic and solid nodules
    • cysts > 3 cm
    • recurring cysts
  41. Extent of Thyroid Surgery Definitions
    • Partial = removal of a nodule with a larger margin of normal thyroid tissue
    • Subtotal = bilateral removal of >50% of each love
    • Lobectomy/hemithyroidectomy = complete removal of one lobe + isthmus
    • Near total = total extracapsular removal of one lobe including isthmus with less than 10% of contralateral lobe left behind
  42. Skin incision for thyroidectomy
    • Standard Kocher's incision
    • (Curvilinear incision along natural Langerhan's line, crease)
    • 4 - 5 cm incision adequate for most cases
    • Carry incision through the the skin and subcutaneous layer through the platysma msucle to the lateral extent of the skin
    • Dissect subplatysmal skin flaps away from the strap muscle
  43. Identification of the RLN
    • identify the inferior thyroid artery
    • Zuckerkandle tuberculum
    • Laterodorsal to Berry's ligament
    • Left RLN runs closer to the tracheoesophageal groov
    • RLN may pass posteriorly or sperficially to the inferior thyroid artery
  44. What is a non-recurrent laryngeal nerve?
    Right side - anomalous right subclavian results in absence of nerve curving back up
  45. Indications for FNA based on ultrasound features
    • High risk history (history of cancer in first degree relative, XRT, prior hemi with +malignancy, MEN2,_ and nodule > 5mm
    • >1 cm solid nodule and hypoechoic
    • > 1 cm and hyperechoic
    • >1.5 cm mixed cystic-solid without suspicious US features
    • >2 cm spongiform nodule
  46. High risk US findings of thyroid nodules:
    • microcalcifications
    • hypoechoic
    • increased nodular vascularity
    • infiltrative margins
    • taller than wide
  47. US guidance for FNA is recommended for nodules that are:
    • Nonpalpable
    • Predominantly cystic
    • Located posteriorly in the thyroid lobe
    • Repeating a nondiagnostic cytology result
  48. Follow-up of nodules that are benign on cytology
    • 5% false negative rate (increased with size >4 cm)
    • serial US q 6 - 18 months after initial FNA
    • If stable (no more than a 50% hange in volume or < 20% increase in at least two nodule dimensions in solid nodules), q3 - 5 years
    • Repeat FNA if significant change
  49. differentiated thyroid cancer includes
    • Papillary
    • Follicular + 3% that are Hurthle cell/oxyphil tumours
  50. Indications for RAI ablation post thyroidectomy
    • T3
    • T4
    • M1
    • RAI in N1 disease is questionable
  51. Primary tumour (T) staging in Thyroid cancer:
    • T1 = <1 cm intrathyroidal or microscopic multifocal
    • OR 1 - 2 cm intrathyroidal
    • T2 = >2 to 4 cm, intrathyroidal
    • T3 = >4 cm in any dimension limited to the thyroid; minimal extrathyroid extension
    • T4a = extending beyond the thyroid capsule to invate subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve
    • T4b = tumour invates prevertebral fascia or encases carotid artery or mediastinal vessels
  52. Regional lymph node staging in Thyroid cancer
    • Nx = cannot be assessed
    • N0 = no regional lymph node metastasis
    • N1 = regional lymph node metastasis
    • a) Metastasis to level VI
    • b) Unilateral or bilateral cervical or mediastinal lymph nodes
  53. Complications of RAI ablation
    • xerostomia
    • sialoadenitis

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