Thyroid and Parathyroid Glands Overview

Thyroid and Parathyroid Glands

• Goiter refers to any thyroid enlargement
• Colloid goiters are common in developed countries, caused by colloid distension
• Idiopathic diffuse or multinodular hyperplasia are other causes of goiter
• Endemic goiters are often linked to iodine deficiency, and are usually asymmetrical and soft
• Anaplastic carcinomas cause hard and firm thyroid swelling, often in the elderly, due to aggressive nature
• Lymphomas of the thyroid can also result in noticeable diffuse enlargement
• Graves' disease presents as a smooth thyroid enlargement
• Hashimoto's thyroiditis results in moderate, firm, and finely nodular enlargement

Solitary Thyroid Nodules

• These can be multinodular on imaging
• Small nodules may be incidental findings, observed during swallowing, as the thyroid moves up and down
• Idiopathic hyperplasia (thyroid adenoma) or thyroid cysts are possible explanations for solitary thyroid nodules
• Simple colloid goiters fall under the category of such nodules
• If a nodule appears during childhood, it most often indicates malignancy and requires exclusion via biopsy (FNA or needle core biopsy)

Hyperthyroidism

• A solitary adenomatous nodule sometimes produces excessive T4 independently of TSH levels
• This is known as a toxic/hot adenoma

Hypothyroidism

• Late result of primary thyroid atrophy (such as in Hashimoto's thyroiditis)
• Inflammation leading to fibrosis and atrophy
• Post-hyperthyroidism treatment with anti-thyroid drugs, radioiodine, or total thyroidectomy can also cause hypothyroidism

Investigating Thyroid Masses

• General thyroid status (euthyroid, hyperthyroid, or hypothyroid) is assessed initially
• Thyroid function tests and thyroid autoantibodies are measured
• Morphology of the gland is investigated (size, shape, consistency, effects on surrounding structures) using ultrasound, plain X-rays, CT scans
• Tissue diagnosis is obtained through FNAc or needle biopsy, incisional/excisional biopsy

Functional Activity of Glandular Tissue

• Radioiodine uptake assessment is used to evaluate thyroid function
• Four patterns can be observed: diffuse homogenous uptake (normal or hyperactive thyroid), generalized patchy uptake (multinodular goiters), cold nodules (likely tumors as they usually don't take up iodine), and hot nodules (toxic adenomas with excessive T4 secretion)
• Radioiodine scanning can help identify ectopic thyroid tissue (in the tongue or along the thyroglossal duct), retrosternal goiters, and metastatic thyroid carcinoma

Surgical Management

• Indicated when a quick and effective cure is needed (e.g., Graves' disease), patient is unresponsive to antithyroid drugs, or if a toxic multinodular goiter is present, preventing suppression of normal thyroid tissue
• Pre-operative assessment includes laryngoscopy to evaluate vocal cord function
• Thyroid function should be normalized before surgery; thyrotoxicosis can trigger cardiac arrhythmias
• Antithyroid medications and Lugol's iodine are given pre-surgery to reduce vascularity and ease excision.

Thyroid Malignancies

• Nearly all originate from follicular cells except for medullary carcinomas
• Papillary and follicular carcinoma are well differentiated, while anaplastic carcinomas are poorly differentiated and more aggressive
• Medullary carcinomas come from parafollicular cells secreting calcitonin
• Lymphomas typically arise from preexisting Hashimoto's thyroiditis

Papillary Carcinoma

• Most common thyroid cancer, affecting women more
• Develops between ages 30-45
• Fibrovascular stroma and psammoma bodies are often present
• Slow-growing and often multicentric

Follicular Carcinoma

• Similar presentation to benign adenomas, so distinction needs histology to confirm capsular or vascular invasion
• More common in women
• Prognosis depends on local invasion extent

Anaplastic Carcinoma

• Extremely aggressive and poor prognosis
• Often found in elderly patients
• Rapidly forms a hard and firm thyroid
• Spreads to trachea, esophagus, regions lymph nodes, and distant sites

Medullary Carcinoma

• Originates from parafollicular C cells, secreting calcitonin
• Presents with hypocalcemia and hypophosphoatamia and potentially other hormones like serotonin and ACTH-like peptides, and can be part of MENII
• Commonly spreads to lymph tissues and organs like lungs, bones, livers
• Resistant to radioiodine therapy and radiotherapy
• Surgically treated with total thyroidectomy and regional lymph nodes removed

Thyroid Lymphomas

• Develops in pre-existing Hashimoto's thyroiditis.
• Diagnosed via needle core biopsy
• Treated with radiotherapy

Goiters (Idiopathic, Non-toxic Hyperplasia)

• Begin as diffuse, micronodular enlargement, later becoming multinodular colloid goiters
• Thyroid cysts and solitary hyperplastic nodules are included in this category
• Usually euthyroid, but can become hyperthyroid if nodules become autonomously active
• Radioiodine scan shows heterogeneous, patchy uptake, due to varying activity of the enlarged nodules
• Surgery may be needed for cosmetic reasons, hyperthyroidism, sudden asymmetric change, compressive symptoms (like stridor or dyspnea), or possible malignancy suspected

Congenital Thyroid Disorders

• Thyroid originates from a midline diverticulum between the first two branchial pouches
• Forms the thyroglossal duct which eventually disappears
• Thyroglossal cysts are midline neck masses, often inferior to hyoid but sometimes submental, that can be diagnosed by asking patient to protrude tongue (cyst moves)
• Ectopic thyroid tissue may be rare, but can be the only thyroid tissue present in a patient, detected by radioiodine scans

Parathyroid

• Lumps from parathyroid glands usually due to hyperparathyroidism
• Common cause is single parathyroid adenoma (benign tumor)
• Diffuse parathyroid hyperplasia involves more than one gland, causing excessive PTH
• Parathyroid carcinoma is rare, leading to hypercalcemia and hypophosphatemia
• Diffuse hyperplasia is a secondary condition, linked to renal failure or vitamin D deficiency
• Surgical management (e.g., removal of affected gland) is the primary treatment for most cases

This quiz covers the essential aspects of the thyroid and parathyroid glands, including conditions such as goiter and hormonal disorders. It examines various types of thyroid enlargement and nodules, their causes, and related diseases like Graves' and Hashimoto's. Test your knowledge on these critical components of the endocrine system.