Thyroid chapter 21

Cysts

10-15 % of solitary nodules are cyst. Almost uniformly benign when < 4mm

Solitary lesion is malignant in __________ cases

10-20% of cases

Vascular supply

4 arteries blood supply: 2 branches of ECA & 2 branches of subclavian arteries. Veins drain into the IJV.

Size of thyroid

4-6 cm long and 2cm in height and width. Larger in women than men. Right lobe is larger than left.

Size of parathyroid gland

5 mm in length , very tiny , flat or disk shaped.

Adenoma

A benign thyroid neoplasm characterized by complete fibrous encapsulation.

Adenoma

A benign thyroid neoplasm characterized by complete fibrous encapsulation. Represents only 5-10% of all nodular disease. Seven times more common in females than in males. May have a halo sign of hypoechoic tissue in the periphery.

Hypervascularity

A cardinal feature of grave's disease

Normal thyroid gland

A fine homogenous echo texture that is slightly more echogenic than surrounding muscle structures.

Thyroid gland Sonographic appearance

A fine homogenous texture that is more echogenic than surrounding muscle structures.

Pyramidal lobe

A small projection extending up from isthmus. About 15 % of whole population has pyramidal lobe.

Secondary hyperparathyroidism

Enlargement of parathyroid glands in patients with renal failure or vitamin D deficiency.

Parathyroid hyperplasia

Enlargement of the multiple parathyroid glands.

Goiter

Enlargement of the thyroid gland can be focal or diffuse.

Ectopic thyroid

Failure of complete migration of thyroid cells during development.

Reasons for ultrasound exam of thyroid

For patients with history of therapeutic radiation to they head or neck. Serial exam to follow up on size of nodules Distinguish between cystic and solid masses Fine-needle aspiration with ultrasound guidance.

Esophagus

Found to the left of trachea. Seen while scanning left lobe of thyroid. Target appearance in transverse plane and by its peristaltic movements when the patients swallow.

Other causes of goiter

Graves' disease Thyroiditis Neoplasm Cyst

Strap muscles

Group of three muscles (sternothyroid, sternothyroid, and omohyoid)

Thyroid anatomy

H-shaped Located in anteroinferior neck at the level of thyroid cartilage. Consist of a right and a left lobe located either side of the trachea. Both lobes connected across midline by the thin bridge called the Ishthmus.

Other causes of hypothyroidism

Hashimoto's thyroiditis ( have increased risk of malignancy) Common enlargement in children.

Parathyroid hormone

Hormone secreted by parathyroid glands that regulates serum calcium levels.

Thyroid stimulating hormone

Hormone secreted by the pituitary gland that stimulates the thyroid gland to secrete thyroxine and triiodothyronine.

Primary hyperparathyroidism is characterized by___________.

Hyper calcemia Hyper calciuria Hypophosphatasia

Signs of malignancy for papillary carcinoma

Hyper vascularity Calcs Taller than its wide

Graves' disease characteristics

Hypermetabolism. Diffuse toxic goiter Exophthalmos Cutaneous manifestations

Hyperthyroidism

Increase in the metabolic rate dramatically

Primary hyperparathyroidism

Increased function of parathyroid glands. Women are 2 to 3 times are more likely to have that. Common after menopause.

Thyroiditis

Inflammation of the thyroid.

Most common cause of hypothyroidism

Iodine deficiency

The mechanism of producing thyroid hormone

Iodine metabolism

Thyroid carcinomas most commonly metastases in ________.

Lungs Bone Regional lymph nodes

Multinodular goiter

Most common cause of thyroid enlargement Most frequent cause is iodine deficiency world wide. Makes glands enlarged

Papillary carcinoma

Most common form of thyroid malignancy.

Hashimoto's thyroiditis

Most common from of thyroiditis Characterized by a destructive autoimmune disorder which leads to chronic inflammation of thyroid. Thyroid appear hypoechoic and coarse , fibrotic overtime

Papillary cancer

Most common of the thyroid malignancies. The preponderant cause of thyroid cancer in children.

Papillary carcinoma

Most common of thyroid malignancies Females are more affected than males Metastases to lymph node in neck (cervical lymphadenopathy).

Medullary carcinoma

Neoplastic growth that account for 10 % of thyroid malignancies.

Multinodular goiter

Nodular enlargement of the thyroid associated with hyperthyroidism

Lymphoma

Non-Hodgkin type. Affects older females Patient has a pre existing Hashimoto's disease. Non-vascular, hypoechoic, lobulated mass.

Sonographic appearance of parathyroid gland

Not readily visualized, unless enlarged , isoechoic to thyroid tissue.

Thyroid function is evaluated by ____________.

Nuclear medicine Cold nodule: one that does not absorb radio pharmaceutics used , appears as absent activity on the nuclear image Cold nodules have 5-15 % chance of being malignant & need to be observed by ultrasound.

Follicular carcinoma

Occurs as a solitary malignant mass within the thyroid gland.

Mutilnodular goiter

One of the most common form of thyroid disease.

Normal lymph node appearance

Oval in shape with a homogenous texture with a central core echo complex.

Primary hyperparathyroidism

Over secretion of parathyroid hormone, usually from a parathyroid Adenoma.

Hyperthyroidism

Oversecretion of thyroid hormones.

When serum calcium level decreases , the parathyroid glands are stimulated to release_____________.

PTH

Hypothyroidism

Under secretion of thyroid hormones.

Medullary carcinoma

Accounts for 5% of thyroid cancers Considered more lethal A high incidence of metastatic involvement of lymph nodes.

Goiter

Also known as nodular hyperplasia and multinodular goiter. Women are more likely to have that men. Modularity may be the end stage of diffuse goiter Hemorrhagic necrosis may occur which gives the thyroid complex look.

Goiter

An enlargement of thyroid gland. Often visible on the anterior neck

Relational anatomy of thyroid

Anterior: Strap muscles Posterior: the carotid sheath with the common carotid artery, internal jugular vein and vagus nerve, longus colli muscle is Medial : larynx, trachea, inferior constrictor of the pharynx, and esophagus.

Lymphadenopathy

Any disorder characterized by localized or generalized enlargement of the lymph nodes or lymph vessels Caused by TB, syphillis, mononucleosis and bacterial infections.

Abscess

Can arise in any location of the neck Ranges from primarily fluid-filled to completely echogenic. Commonly appear as a mass of low-level echogenicity.

Graves' disease

Autoimmune disorder characterized by a diffuse toxic goiter, bulging eyes, and cutaneous manifestation.

Adenoma

Benign thyroid neoplasm characterized by complete fibrous encapsulation.

PTH acts on ____________ and intestine to enhance calcium absorption

Bone and kidney

Exophthalmus

Bulging eyes and retraction of eyelids Presence may be a sign of Graves' disease Women>30 years old Ratio of females to males is 8:1 Presence of exophtalmus differentiate toxic adenomas form Graves' disease.

Function of parathyroid gland

Calcium monitors of the body Produce parathyroid hormone (PTH) which keep the serum calcium level stable. Prevent hyper or hypo calcemia.

The parathyroid gland are ___________organs in the body

Calcium-sensing

Swallowing make the thyroid tissue go in __________ direction

Cephalad.

Hashimoto's thyroiditis

Chronic inflammation of the thyroid gland caused by the formation of antibodies against normal thyroid tissue.

Thyroid hormones are stored in __________.

Colloid of the gland.

Thyroglossal duct cyst

Congenital anomalies that appear in the midline of neck anterior to the trachea. Oval or spherical masses rarely larger than 2 or 3 cm

Thyroglossal duct cysts

Congenital anomalies that present in the midline of the neck anterior to the trachea.

Cleft cyst

Cyst and fistulas may form when the thyroglossal duct fails to atrophy after embryological migration of the thyroid gland

Ultrasound is most useful in differentiating _________ from _________.

Cystic ; solid lesions.

Cysts in the thyroid me be formed from __________.

Cystic degeneration of follicular adenomas.

Nodular hyperplasia

Degenerative nodules within the thyroid.

Hypoparathyroidism

Disorder associated with elevated serum calcium level, usually caused by a benign parathyroid Adenoma.

Lymphadenopathy

Disorder characterized by a localized or generalized enlargement of the lymph nodes or lymph vessels.

Thyroid development

Earliest endocrine structure in human embryo. Distinguished at 16-17 days gestation Cells migrate downward and divide into 2 lobes with an isthmus at 7 wks.

Serum calcium

Laboratory value that is elevated with hyperparthyroidism.

Sternocleidomastoid muscles

Large muscles anterolateral to the thyroid

The muscle posterior to the thyroid is ____________.

Longus colli muscle

Other structures mistaken for parathyroid gland

Longus colli muscle, esophagus, and the neuromuscular bundles.

Hypophosphatasia

Low phosphate level associated with hyperparthyroidism.

Function of thyroid gland

Maintain body metabolism , growth and development through synthesis , storage and secretion of thyroid hormone.

Lab tests

Measure the free fraction of the hormone directly in the blood.

Anaplastic (undifferentiated) carcinoma

Most aggressive Occurs most commonly in elderly population. Hard , fixed mass with rapid growth. Cause death by compression and asphyxiation due to invasion of the trachea.

Adenoma

Most common cause of primary hyperparathyroidism. Tumor associated with a history of exposure to ionizing radiation. Sonographically well circumscribed nodules at posteromedial border of thyroid.

The parathyroid glands are normally located on the ____________ surface of the thyroid gland.

Posterior medial

Pyramidal lobe

Present in small percentage of patients Extends superiorly from the Isthmus.

Function of parathyroid gland

Produce parathyroid hormone and monitor serum calcium feedback mechanism.

RIA

Radio immunoassay Nuclear medicine study to accurately measure levels.

Possible signs of malignancy with goiter

Rapid growth of the gland and ensuing hoarseness.

Thyroid carcinomas

Rare, solitary , solid lesion more than multiple Female to male ration 2:1 Calcifications are present in 50-80 % of patients

Anaplastic carcinoma

Rare, undifferentiated carcinoma occurring in middle age.

Euthyroid

Refers to a normal functioning thyroid gland.

Brachial cleft cyst

Remnant of embryonic development that appears as a cyst in the neck .

Sonographic evaluation of thyroid

Review patient history Ask if nuclear medicine test was done Supine, pillow under both shoulders to provide moderate hyper extension of the neck. High frequency linear transducer (10-12 MHz) Use color Doppler.

Cystic hygroma

Secondary to reabsorbed prenatal cystic hygroma . Conjunction with turner's syndrome.

Types of thyroid hormones

T3: triiodothyronine T4: thyroxine Calcitionin.

Isthmus

Small piece of thyroid tissue that connects the right and left lobes of the gland

Three parts of strap muscles

Sternohyoid muscle Sternothyroid muscle Omohyoid muscle

Along the anterior surface of thyroid gland lie the ___________muscles.

Strap muscles

Hypothyroidism

The inability of the thyroid to produce the proper amount of thyroid hormone or a problem in the pituitary gland that does not control the thyroid production.

Follicular carcinoma

The second subtype of well-differentiated thyroid cancer Two types : minimally invasive & widely invasive . Solitary mass and more aggressive than papillary cancer. Occurs in people over 50 yrs.

Calcitonin

Thyroid hormone important for maintaining a dense, strong bone matrix and regulating the blood calcium level. Helps to maintain homeostasis of blood calcium and help prevent an excess of calcium in the blood.

Diagnosis of Graves' disease

Thyroid may or may not be enlarged Usually inhomogenous and hypoechoic without nodules. Hypervasculariy A thrill or bruit can be heard over the gland called thyroid inferno.

TSH

Thyroid-stimulating hormone Produced by pituitary gland.

Microcalcification

Tiny echogenic foci within a nodules that may or may not shadow

Most common cause of hyperthyroidism

Toxic adenomas Graves' disease

Fine-needle aspiration

Use of a fine-gauge needle to obtain cells from a mass.

Parathyroid gland anatomy

Usually 4, tiny endocrine gland embedded in posterior/medial thyroid gland Commonly 2 pairs which lie behind the middle and lower third of the thyroid.

Subacute (DeQuervain's) thyroiditis

Viral infection of the thyroid that causes inflammation.

Signs and symptoms of hypothyroidism

Weakness, fatigue, dry skin, cold intolerance , hoarseness, weight gain , menstrual irregularities , constipation and decreased sweating.

Longus colli muscles

Wedge-shaped muscle posterior to the thyroid lobes. Appears as hypoechoic triangular structure adjacent to cervical vertebrae.

Clinical signs of Hyperthyroidism

Weight loss, Increased appetite High degree of nervous energy , Tremor Excessive sweating , Heat intolerance Palpitations Exophathalmos (protrusion of eyes)