1. Neoplasms
1.1. Bengin
1.1.1. well-encapsulated
1.1.2. expansile growth pattern
1.1.3. Types
1.1.3.1. Follicular adenomas
1.1.3.1.1. discrete, solitary mass
1.2. Malignant
1.2.1. Uncommon but good prognosis
1.2.2. Types
1.2.2.1. Papillary (85%)
1.2.2.1.1. Rearrangements of the tyrosine kinase receptors RET or NTRK1 or activating point mutations in BRAF.
1.2.2.1.2. > Women (25-50)
1.2.2.1.3. un-encapsulated, infiltrative and may be multifocal
1.2.2.1.4. Risk factor: exposure to ionizing radiation
1.2.2.1.5. Features: 1. Papillary structures 2. Psammoma bodies 3. Grooved nuclei 4. Orphan Annie nuclei 5. Pseudoinclusions
1.2.2.2. Follicular (15%)
1.2.2.2.1. Mutations in RAS (oncogenes)
1.2.2.2.2. > Women (40-60)
1.2.2.2.3. More frequent in areas with dietary iodine deficiency
1.2.2.2.4. Metastasis: most commonly in the lung or bones.
1.2.2.2.5. Features: 1. Solitary encapsulated 2. closely packed small follicles 3. Degenerative changes (central fibrosis and foci of calcification) sometimes present.
1.2.2.3. Medullary (5%)
1.2.2.3.1. Familial medullary thyroid carcinomas occur in multiple endocrine neoplasia type 2 (MEN-2) RET (protooncogene mutation)
1.2.2.3.2. Derived from the C-cells, neuroendocrine tumor, secretes calcitonin
1.2.2.3.3. Features: 1. sporadic neoplasms originate in one lobe, bilaterality and multicentricity are common in familial cases. 2. necrosis and haemorrhage, firm, pale gray to tan, and infiltrative.
1.2.2.4. Anaplastic (<5%)
1.2.2.4.1. Inactivating point mutations in the p53 (tumor suppressor) gene
1.2.2.4.2. rapid growth rate, Lethal (100%)
1.2.2.4.3. older age group > 65 year
1.2.2.4.4. Undifferentiated tumors Can be arising from papillary carcinoma
1.2.2.4.5. Features: Highly anapaestic cells, Large, pleomorphicgiant cells, occasional osteoclast-like multinucleate giant cells, Spindle cells with a sarcomatous appearance, Mixed spindle and giant cells.