Thyroid Gland Anatomy, Physiology, and Pathology

Flashcards of key vocabulary and concepts from a lecture on the anatomy, physiology, and pathology of the thyroid gland.

Thyroid Anatomy

Composed of two lobes connected by an isthmus; Weighs 15-25 grams; Lobe dimensions approx. 40/20/20-40 mm; Isthmus thickness approx. 2-6 mm.

Thyroid Lobe Ratios

Medial: larynx, trachea, pharynx, esophagus. Lateral: anterior cervical musculature. Posterior: cervical neurovascular package, recurrent nerve, parathyroid glands.

Thyroid Location

Attached to trachea and larynx with ligaments and fascia; situated between sheets of anterior and posterior cervical deep aponeurosis in the thyroidian lodge.

Thyroid Isthmus

Located on tracheal rings 2-3.

Pyramidal Lobe

Extends cranially from isthmus, remnant of thyroglossal duct, present in 80% on left paramedian.

Superior Thyroid Artery

Arises from the external carotid artery.

Inferior Thyroid Artery

Arises from the thyreo-bicervico-scapular trunk.

Middle Thyroid Artery

Inconstant; arises from the common carotid artery.

lymphatic drainage of thyroid

Superficial cervical lymph nodes, deep cervical lymph nodes, and mediastinal lymph nodes.

Thyroid Innervation

Superior and middle cervical sympathetic chain; parasympathetic fibers of the vagus nerve via laryngeal nerve.

Thyroid Lobules

Contain many follicles (20-40); connective tissue rich in vessels and nerves. Follicles are spherical with cuboid epithelium, containing colloid.

Cell C (Parafollicular)

Produces calcitonin.

Thyroid Hormones

Thyroxine (T4) and triiodothyronine (T3).

Thyroid Hormone Actions

Increases metabolic rate, O2 consumption, carbohydrate metabolism, lipid metabolism, and protein catabolism.

Iodine Need

0.1 mg in food.

Iodine-Rich Foods

Fish, milk, eggs.

Thyroid Hormone Production

Iodine combines with tyrosine to form MIT (monoiodotyrosine) and DIT (diiodotyrosine); T3 is formed from MIT + DIT, and T4 from DIT + DIT.

T3

triiodothyronine (MITH + DITH)

T4

tetraiodtyroxine (DITH + DITH)

Acute Thyroiditis

Rare; often associated with respiratory inflammation or systemic infections. Etiologic agents: streptococcus, staphylococcus, pneumococcus, E. coli, Coccidioides immitis.

Lymphomatous Thyroiditis (Hashimoto)

Most common chronic thyroiditis; autoimmune; associated with SLE, RPA, myasthenia gravis, hemolytic anemia, papillary carcinoma.

Hashimoto clinical picture

Insidious increasing volume , neck pain, dyspnea, dysphagia, asthenia , hypothyroidism

Woody Chronic Thyroiditis (Riedel)

Rarest of chronic thyroiditis; associated with mediastinal or retroperitoneal fibrosis; characterized by lobar or diffuse fibrosis.

Goiter

Hypertrophy of dystrophic nature affecting parenchyma and/or glandular stroma in the absence of neoplastic, inflammatory, or parasitic processes

goiter definition

hypertrophy of dystrophic nature that interested parenchyma and / or glandular stroma in the absence of any neoplastic process, inflammatory or parasitic

Congenital Goiter

Familial enzyme defects.

Acquired Goiter - Endemic

Iodized water deficiency areas.

Acquired Goiter - Sporadic

Less than 10% of population; causes include goitrogenic foods and drugs.

Goiterogenesis

Decreased T3, T4 leads to increased TSH, which increases thyroid volume.

Topographic Forms of Goiter

Normotopical, ectopic (lingual, medial submandibular, laterocervical), aberrant congenital (mediastinal endothoracic, ovarian), endothoracic plunging goiter.

Clinical Picture of Giter

Asymptomatic or feeling of pressure + cervical tumor increasing in size. May cause dysphagia, dyspnea, facial erythema, dysphonia.

WHO Classification of Goiter

Grade I (small), Grade II (middle), Grade III (large), Grade IV (voluminous).

Morphological Examinations for Goiter

Cervical Rx (calcifications, tracheal deviation), Chest Rx (mediastinal widening), Esophageal barium Rx (esophageal compression), Thyroid scintigraphy (functional activity).

Imaging Exams for Goiter

Cervical ultrasound (confirms goiter, characterizes nodules), CT Scan, MRI, Fine needle aspiration cytology (FNAC).

Functional Exploration

Radioactive iodine uptake (RIC): v.n. = 20% at 2 h, 30-40% at 24 h; iodine dosage of protein, T3, T4.

Positive Diagnosis of Goiter

Morphological (parenchymal or nodular), Functional (normo, hypo, or hyperthyroidism), Stage (oligosymptomathic, endocrinopathic, visceropathic, neuropathic).

Solitary Thyroid Nodule

Benign lesions 90-95% (adenoma, colloidal node). Malignant lesions 5-10% (primitive thyroid cancer, metastases).

Risk Factors for Thyroid Cancer

Previous irradiation, male, family history, age

Hyperthyroidism

Increasing free thyroid hormones, resulting in thyrotoxicosis.

Clinical Forms of Hyperthyroidism

Basedow-Graves disease, multinodular toxic goiter, toxic thyroid nodule, others (thyroid hormone ingestion, struma ovarii).

Basedow-Graves Disease

Autoimmune disease; antithyroid antibodies (Ig) against TSH receptor; causes  thyroid hormons.

Clinical Treatment for Hyperthyroidism

The methods are medical antithyroidian drugs, thyroid ablation with radioactive I131 and surgey.

Medical Treatment of Hyperthyroidism

beta blockers - propranolol (reduce heart rate, tremor controls, relieves nervous irritation); antithyroid drugs – propylthiouracil, methimazole, carbimazole(blocks thyroid hormone synthesis at different levels).

Thyroidian Cancer

Most frequent localisation of malignant tumors of the endocrine system (1% of all cancers). Types: differentiated carcinoma (papillary, follicular, medulary) and Undifferentiated carcinoma.

ages scale:

age, tumoral grading, disease extension, tumor size

Papillary Thyroid Carcinoma Treatment

Thyroidian lobectomy with isthmectomy or Total thyroidectomy with cervical lymphadenectomy .

Follicular Carcinoma (vesicular)

2nd most frequent among thyroid cancers ; More frequent in female sex (3:1); Adult age 50-60 years. There are two main types - Encapsulated and frankly invasive .

Surgical treatment Follicular Carcinoma

Thyroid lobectomy including isthmus and pyramidal lobe ; Total thyroidectomy– Surgery of choice in follicular thyroidian cancerexcepting minimal forms