THYROID ANATOMY AND PATHOLOGY

Muni Venkatesh.PGroup 2

ANATOMY

It is an endocrine gland.

Located in the anterior region of the neck at C5-T1, overlays 2nd – 4th 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.

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

PYRAMIDAL LOBE

Often ascends from the isthmus or the adjacent part of either lobe up to the hyoid bone

May be attached by afibrous/fibromuscular

band “levator” of the thyroid gland.

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.

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.

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

MUSCULAR LANDMARKS

a. Sternocleidomast -oid muscles lie laterallyb. Longus collimuscles lie posteriorly c.Strap muscle, omohyoid muscle andsternohyoid muscles lie anteriorly

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

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.

AUTONOMIC INNERVATION

a.Cervical portion of sympathetic trunkb.Parasympatheticfibers arise from Vagus X

DISEASES OF THE THYROID GLAND

Congenital diseases

Inflammation

Functional abnormality

Diffuse and Multinodular goiters

Neoplasia

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

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

HASHIMOTO THYROIDITISPATHOGENESIS

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

Outcome: progressive depletion follicular cells with

replacement by mononuclear inflammation and

fibrosis

HASHIMOTO THYROIDITIS

Diffuse enlargement

Firm or rubbery

Pale, yellow-tan, firm & somewhat nodular cut surface

HASHIMOTO THYROIDITIS

Massive lymphoplasmcyticinfiltration with lymphoid follicles formation

Destruction of thyroid follicles

Remaining follicles are small and many are lined by Hurthle cells

Increased interstitial connective tissue

FUNCTIONAL ABNORMALITY

Hyperfunction

in level of hormone → toxic effects

Due to:

Diffuse hyperplasia

Hyperfunctioning multinodular goiter

Hyperfunctioning adenoma

Subacute lymphocytic (painless) thyroiditis

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

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.

LABORATORY

Serum TSH level.

Free serum T3 and T4.

Detection of anti-thyroid peroxidaseautoantibody.

Detection of TSH receptor-blocking antibody.

By ultrasound.

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 thyroiditisare changes in menstrual cycle, increse risk of abortions etc.