Thyroid anatomy and pathology

thyroid

1. THYROID ANATOMY AND PATHOLOGY Muni Venkatesh.P Group 2

2. ANATOMY It is an endocrine gland. Located in the anterior region of the neck at C5-T1, overlays 2 nd – 4 th tracheal rings . Anterior & lateral to larynx and trachea . Average width: 12-15 mm (each lobe) Average height: 50-60 mm long Average weight: 25-30 g in adults.

3. It has two lobes, which are connected by isthumus . 1.25 cm x 1.25 cm Crosses tracheal rings between 2 and 4 Occasionally absent Pyramidal lobe may be present

4. Pyramidal lobe Often ascends from the isthmus or the adjacent part of either lobe up to the hyoid bone May be attached by a fibrous/ fibromuscular band “ l evator ” of the thyroid gland.

5. structure Gland is covered by capsule. Capsule extensions within the gland form septae , dividing it into lobes and lobules. Lobules contains follicles(structural units of the gland). Follicles are surrounded by dense plexuses of fenestrated capillaries, lymphatic vessels, and sympathetic nerves .

6. Lobules are attached to cricoid cartilage by ligaments Medial surface adapted to larynx and trachea Lobes related posteriorly to the esophagus Posterolateral surface a. related to carotid sheath b. overlaps carotid artery .

7. Epithelial cells = 2 types: principal ( ie : follicular) – formation of colloid ( iodothyroglobulin ) parafollicular ( ie : C cells -clear, light), lie adjacent to follicles w/in basal lamina  produce calcitonin

8. Muscular landmarks a . Sternocleidomast - oid muscles lie laterall y b . Longus colli muscles lie posteriorly c.Strap muscle, omohyoid muscle and sternohyoid muscles lie anteriorly

9. Blood supply Highly vascular gland supplied by four large arteries a . Right & Left inferior thyroid artery b . Right & Left superior thyroid artery Drained by Right & Left superior, middle and inferior thyroid veins a . Veins arise from plexus b. on anterior surface of gland c. Extend over anterior surface of trachea

10. Lymph vessels 1 . In interlobular connective tissue between lobes. 2 . Connect with network in wall of gland 3.Terminate in thoracic and right lymphatic ducts.

11. Autonomic innervation a.Cervical portion of sympathetic trunk b.Parasympathetic fibers arise from Vagus X

12. Diseases of the Thyroid Gland Congenital diseases Inflammation Functional abnormality Diffuse and Multinodular goiters Neoplasia

13. Inflammation Thyroiditis Acute illness with pain Infectious Acute Chronic Subacute or granulomatous (De Quervain’s ) Little inflammation with dysfunction Subacute lymphocytic thyroiditis Fibrous (Riedel) thyroiditis Autoimmune Hashimoto thyroiditis

14. HASHIMOTO THYROIDITIS Most common cause of hypothyroidism Autoimmune, non- Mendelian inheritance 45-65 years, F:M = 10-20:1 Painless symmetrical enlargement Risk of developing B-cell non-Hodgkin’s lymphoma Other concomitant autoimmune diseases Endocrine and non-endocrine

15. Hashimoto Thyroiditis Pathogenesis Immune systems reacts against a variety of thyroid antigens Progressive depletion of thyroid epithelial cells which are gradually replaced by mononuclear cells → fibrosis Immune mechanisms may includes: CD8+ cytotoxic T cell-mediated cell death Cytokine-mediated cell death Binding of antithyroid antibodies → antibody dependent cell-mediated cytotoxicity

16. Outcome: progressive depletion follicular cells with replacement by mononuclear inflammation and fibrosis

17. Hashimoto Thyroiditis Diffuse enlargement Firm or rubbery Pale, yellow-tan, firm & somewhat nodular cut surface

18. Hashimoto Thyroiditis Massive lymphoplasmcytic infiltration with lymphoid follicles formation Destruction of thyroid follicles Remaining follicles are small and many are lined by Hurthle cells Increased interstitial connective tissue

19. Functional Abnormality Hyperfunction  in level of hormone → toxic effects Due to: Diffuse hyperplasia Hyperfunctioning multinodular goiter Hyperfunctioning adenoma Subacute lymphocytic (painless) thyroiditis

20. Functional Abnormality Hypofunction  in level of hormone → impair development in infants and slowing of physical and mental ability in adults Due to: Postablation Surgery Radiation Autoimmune thyroiditis Drugs Dyshormonogenetic

21. Symptoms   Myxedematous psychosis , weight gain,  depression ,  mania , sensitivity to heat and cold,  paresthesia , chronic fatigue, panic attacks,  bradycardia ,  tachycardia , high cholesterol, reactive hypoglycemia , constipation, migraines, muscle weakness, joint stiffness,  menorrhagia , cramps, memory loss, vision problems, infertility and hair loss.

22. Laboratory Serum TSH level. Free serum T3 and T4. Detection of anti-thyroid peroxidase autoantibody. Detection of TSH receptor-blocking antibody . By ultrasound.

23. Treatment The normal thyroid hormone level is maintained by giving thyroxine therapy which will also help to reduce side of thyroid gland. Complications of Hashimoto’s thyroiditis are changes in menstrual cycle, increse risk of abortions etc.