Thyroid and Parathyroid

• 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

• 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

4th branchial pounches

Caudal tract remnant of the thyroglossal duct

Failure of migration or excessive descent

Complete arrest of the descent of the developing thyroid with resulting presence of thyroid tissue at the tongue base

• Debate whether lateral neck thyroid tissue represents normal thyroid tissue versus metastatic thyroid carcinoma
• treated as thyroid cancer with resection

• 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

• Thyroiditis
• e.g. Hashimoto Thyroiditis and Riedel Thyroiditis
• Adenomas
• Goiters

• Chronic lymphocytic Thyroiditis (Hashimoto Thyroiditis)
• - antibodies to thyroid peroxidase and thyroglobulin

- rare disorder characterized by fibrosis of the thyroid gland

immunologically mediated thyroid cell dmamage by autoantibodies against thyroid peroxidase and thyroglobulin and TSH receptor

• can occur at any age
• most common cause of hypothyroidism

• Follicular adenoma
• Hurthle Cell adenoma
• Hyalinizing trabecular adenoma
• Nodular (adenomatous) goiter

• Papillary carcinoma
• Follicular carcinoma
• Hurthle-cell Variant
• Medullary thyroid carcinoma
• Anaplastic thyroid carcinoma

• Ill-defined margins
• Firm consistency
• Whitish colour
• Granular cut surface

• Papillae
• Subtle irregularities in the nuclear contours
• Pseudoinclusions with cytoplasmic invaginations
• Psammoma bodies

• Papillary thyroid microcarcinoma
• Follicular variant
• Encapsulated variant
• Diffuse sclerosing variant
• Oxyphilic cell variant
• Tall-cell variant
• Columnar cell variant

• Multicentric involvement
• Extrathyroidal extension is common
• (muscle, RLN, and trachea)
• Lymph node involvement in 30%
• <5% have distant metastasis at time of diagnosis

• Previous ionizing radiation (e.g. head and neck irradiation for childhood lymphoma)
• Syndromes involving familial PTC: Cowden syndrome
• Family history

Multiple hamartomas, breast tumours, and follicular/papillary thyroid tumours

• 13% of all thryoid carcinomas
• 10-year survival is 60%
• 10 to 15% present with distant metastasis
• Less nodal metastasis

96%

• solitary tumours
• thick fibrous capsule
• hypercellualr
• Frozen section is often not sufficient for diagnosis
• FNA not helpful

• Minimally invasive
• Widely invasive

• Radiation exposure
• Chronic goiter secondary to hypothyroidism

• 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

• Presents with thyroid mass or nodule
• 35% of patients develop distance metastasis at some point

• <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

• Rapidly expanding neck mass or sudden changein size of preexisting goiter
• May have associated symptoms of dysphagia, hoarseness, dyspnea, cough, pain
• Horner's syndrome

• large, bulky infiltrative masses
• gray-white
• fibrous with areas of focal necrosis and hemorrage

• Spindle cell
• Giant cell
• pleomorphic
• Malignant fibrous
• Histiocytic
• Squamoid cell

• <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

• Cannot distinguish between benign microfollicular adenomas and differentiated FTCs
• Cannot differentiate Hurthle cell lesion from Hashimoto thyroiditis

• trabecular
• follicular
• microfollicular
• solid

• Risk of Malignancy
• Benign <1%
• Atypia of US 5 - 10%
• Neoplasm 20 - 30%
• Suspicious for Malignancy 50 - 75%
• Malignant 100%
• Non-diagnostic

• 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)

• High accuracy (90 - 100%)
• False positive of <1%
• False negative rates of 1 - 11%
• Safe, inexpensive, easily performed, minimal patient discomfort

• 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

• Low risk of malignancy if simple cysts (1 - 4%)
• Higher risk if:
• mixed cystic and solid nodules
• cysts > 3 cm
• recurring cysts

• 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

• 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

• 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

Right side - anomalous right subclavian results in absence of nerve curving back up

• 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

• microcalcifications
• hypoechoic
• increased nodular vascularity
• infiltrative margins
• taller than wide

• Nonpalpable
• Predominantly cystic
• Located posteriorly in the thyroid lobe
• Repeating a nondiagnostic cytology result

• 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

• Papillary
• Follicular + 3% that are Hurthle cell/oxyphil tumours

• T3
• T4
• M1
• RAI in N1 disease is questionable

• 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

• 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

• xerostomia
• sialoadenitis