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i. Usually painless, solitary nodules ii. "Cold nodule" on thyroid scans iii. May be functional and cause hyperthyroidism (toxic adenoma)

2. Papillary carcinoma a. Epidemiology i. Account for 80% of malignant thyroid tumors ii. Females > males; age 20-50

iii. Risk factor: radiation exposure b. Micro i. The tumor typically exhibits & papillary pattern ii. Occasional psammoma bodies iii. Characteristic nuclear features

• Clear "Orphan Annie eye" nuclei

• Nuclear grooves

• Intranuclear cytoplasmic inclusions c. Lymphatic spread to cervical nodes is common d. Treatment i. Resection is curative in most cases ii. Radiotherapy with iodine 131 is effective for metastases e. Prognosis: excellent; 20-year survival = 90%

3. Follicular carcinoma a. Accounts for 15% of malignant thyroid tumors b. Females > males; age 40-60

c. Hematogenous metastasis to the bones or lungs is common

4. Medullary carcinoma a. Accounts for 5% of malignant thyroid tumors b. Arises from C cells (parafollicular cells) and secretes calcitonin c. Micro: nests of polygonal cells in an amyloid stroma d. Minority (25%) are associated with MEN II and MEN III syndromes (see Multiple Endocrine Neoplasia Syndromes)

5. Anaplastic carcinoma a. Presentation i. Females > males; age >60

ii. Firm, enlarging, bulky mass iii. Dyspnea and dysphagia iv. Tendency for early widespread metastasis and invasion of the trachea and esophagus b. Micro: undifferentiated, anaplastic, and pleomorphic cells c. Prognosis: very aggressive and rapidly fatal

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F. Parathyroid Glands

1. Primary hyperparathyroidism a. Etiology i. Parathyroid adenoma (80%); may be associated with MEN I and II

ii. Parathyroid hyperplasia (15%)

• Diffuse enlargement of four glands

* Usually composed of chief cells iii. Parathyroid carcinoma (very rare)

iv. Paraneoplastic syndrome: lung and renal cell carcinomas b. Pathogenesis: excess production of parathyroid hormone (PTH) leads to hypercalcemia c. Clinical features i. Lab: elevated serum calcium and PTH

ii. Often asymptomatic iii. Kidney stones iv. Osteoporosis and osteitis fibrosa cystica v. Metastatic calcifications vi. Neurologic changes

2. Secondary hyperparathyroidism a. Etiology i. Chronic renal failure ii. Vitamin D deficiency iii. Malabsorption b. Pathogenesis: caused by any disease that results in hypocalcemia, leading to increased secretion of PTH by the parathyroid glands

3. Hypoparathyroidism a. Etiology i. Surgical removal of glands during thyroidectomy ii. DiGeorge syndrome iii. Idiopathic b. Clinical features i. Lab: hypocalcemia ii. Neuromuscular excitability and tetany: Chvostek's and Trousseau's signs iii. Psychiatric disturbances iv. Cardiac conduction defects (ECG: prolonged QT interval)

c. Treatment: vitamin D and calcium

G. Pituitary Gland

1. Pituitary adenomas a. ProlactijQoma i. Most common type ii. Galactorrhea, amenorrhea, and infertility iii. Decreased libido and impotence

ClinicalCorrelate

Pituitary adenomas may be associated with MEN I.

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