Thyroid Encyclopedia: Encyclopedia of Thyroid Disease, Thyroid Conditions and Thyroid Cancer

By Alexander Shifrin and Svetlana Krasnova

The Thyroid Encyclopedia is intended to help all patients, and their family members, to better understand thyroid diseases, thyroid cancer, and thyroid problems. The goal of this book is to educate the patient, as well as help them understand all aspects of their disease and treatment process.
Most of the time patients have questions related to the interpretation of their specific test results, the meaning of specific medical terms of their diagnosis, and their treatment plan. A majority of patients, who are reading their own laboratory, radiology, or pathology reports, are not familiar with specific medical terminology related to the thyroid gland and thyroid disease. Sometimes, physicians and health care providers are not available to discuss, or do not have enough time to explain to the patient and interpret all nuances of their diagnosis, test results, or treatment plan. Throughout my 15 years practicing thyroidology (treating patients with thyroid diseases), I have realized that there is not enough information presented to patients during their visits and that patients still have multiple questions leaving their appointments. There is no specific designated practice provider who can explain and interpret to the patient all specific terminology related to her/his disease. The idea to educate and to help the patient along throughout their journey and through their cure is the main reason that the Thyroid Encyclopedia came alive.

• Language: English
• Publisher: Balboa Press
• Release date: Apr 4, 2022
• ISBN: 9798765225387

Alexander Shifrin

Alexander Shifrin, MD, FACS, FACE, ECNU, FEBS (Endocrine), FISS Clinical Associate Professor of Surgery, Rutgers RWJ Medical School; Associate Professor of Surgery, Hackensack Meridian School of Medicine; Director of Endocrine Oncology at Hackensack Meridian Health of Monmouth and Ocean Counties; Surgical Director, Center for Thyroid, Parathyroid and Adrenal Diseases; Jersey Shore University Medical Center After completing General Surgery Residency Program from superb academic universities, University of Pennsylvania and Penn State Milton S Hershey Medical Center, and two fellowships, Surgical Critical Care at Penn State and then Endocrine Surgery Fellowship at Columbia New York Presbyterian Hospital, in 2006 he established the first Endocrine Surgery Program in New Jersey at Jersey Shore University Medical Center. With more than 15 years’ experience as an Endocrine Surgeon and the leader of the busiest and the most successful Endocrine Surgery Program in New Jersey, he was elected as a Vice President of the New Jersey Chapter of the American Association of Clinical Endocrinologists and become one of the first surgeons granted the status of the Fellow of the International Society of Surgery (FISS). He has attained three Board Certifications: • by the American Board of Surgery (ABS), • by the American College of Endocrinology in Endocrine Neck Ultrasound and Ultrasound Guided Thyroid Biopsy (ECNU), • by the European Board of Endocrine Surgery (FEBS). One of the most successful parts of his academic career was his publishing experience. Beside multiple medical articles in peer-reviewed medical journals, he has published several medical books and atlases. Completing an extensive list of publication including seven endocrine surgery books within the past three years as the editor: • “Atlas of Adrenal Surgery" by Springer • “Advances in Treatment and Management in Surgical Endocrinology” by Elsevier • “Avances en endocrinología quirúrgica” Spanish Edition by Elsevier • “Atlas of Parathyroid Surgery" by Springer • “Atlas of Parathyroid Imaging and Pathology” by Springer • “Endocrine Emergencies” by Elsevier • “Endocrine Surgery Comprehensive Board Exam Guide” by Springer • “Atlas of Thyroid Surgery” by Springer. Collaboratively publishing the first Endocrine Surgery Board Exam preparation manuscript, “Endocrine Surgery Comprehensive Board Exam Guide” was a detailed and complicated process involving managing collaborative efforts of world leaders in Endocrine Surgery, and the international community through Springer publisher. Svetlana Krasnova, RN, MSN, FNP-C, RNFA, CNOR. Family Nurse Practitioner who has been working at the Department Otolaryngology- Head and Neck Surgery at Rutgers University School of Medicine. She graduated at the top of her class with Honors in Master’s Degree in Nursing from Georgian Court University, and then received Advance Nurse Practitioner Degree as Family Nurse Practitioner (Adult and Pediatric) from Monmouth University. She published several book chapters on thyroid diseases.

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Copyright © 2022 Alexander Shifrin; Svetlana Krasnova.

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ISBN: 979-8-7652-2537-0 (sc)

ISBN: 979-8-7652-2539-4 (hc)

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Balboa Press rev. date: 03/30/2022

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CONTENTS

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Z

About the authors

About the Book

A

AACE

The American Association of Clinical Endocrinologists (AACE) is a professional organization of physicians specializing in endocrinology, diabetes, and metabolism committed to enhancing the ability of its members to provide the highest quality of patient care.

AAES

The American Association of Endocrine Surgeons (AAES) is a professional organization of physicians and allied health professionals dedicated to the advancement of the science and art of endocrine surgery. Active members are board-certified surgeons and allied health professionals who have clinical expertise and research interests related to the thyroid, parathyroid, adrenals, and neuroendocrine tumors of the pancreas and gastrointestinal tract. The organization partakes in patient care, education, and scientific investigations in the field of endocrine surgery, including training endocrine surgeons and developing practice guidelines.

Ablation

(see Ethanol ablation)

Ablation means removal or destruction (destroying completely) of a tumor by using energy (radiation), different chemicals, or other techniques.

Active surveillance (Fig. 1)

Active surveillance means close monitoring without surgical intervention. It involves close monitoring of the patient with thyroid cancer over time instead of treating the cancer with immediate surgery. A treatment plan is developed with a multidisciplinary group of practitioners involved in the care of the particular patient with thyroid cancer. It includes conscious consent of the patient and patient’s understanding of the plan. Active surveillance involves closely watching the condition of a patient known for or suspected of having a thyroid cancer, cancer metastases (spread), or cancer recurrence, but not giving any treatment such as surgery or radioactive iodine. If during the course of surveillance there is a change in the size of the tumor, test results, or other results that show that the cancer is progressing or getting worse, then the surveillance is replaced with a more active treatment plan and specific therapy is implemented (surgical removal, radioactive iodine therapy, or other chemical or drug therapy). For example, if there’s an increase in the size of the tumor seen on ultrasound, or any other radiological studies, or tests showing an elevation of tumor markers (thyroglobulin or calcitonin), then surveillance is replaced with a more active treatment plan.

Active surveillance has recently been implemented as an option due to findings that thyroid cancer incidences are increasing, with the majority presenting in patients as small, clinically not significant papillary thyroid cancers. Patients have been shown to have a low risk of cancer progression if found very small and incidental. In addition, the rate of recurrence of this small, incidental thyroid cancer after the initial surgery is low. Studies have shown that if patients are followed with regular ultrasound exams, there is no difference in long-term outcomes (such as morbidity or mortality) compared to similar patients who have surgery. With the literature in mind, the recent guidelines by the American Thyroid Association have suggested that active surveillance could be considered as an alternative to surgery in patients with low risk micro papillary thyroid cancer (less than 1 cm).

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Figure 1. Active surveillance. Positive by biopsy, metastatic neck lymph node from the papillary thyroid carcinoma (PTC). Lymph node was followed for 8 months with the thyroid ultrasound and showed no changes in size and appearance. A, B – ultrasound images showing the first observation (A – longitudinal view; B - transverse view); C, D - ultrasound of the same lymph nodes on 8 months follow up showing no changes in size and appearance (C – longitudinal view; D - transverse view).

Acoustic shadow (on thyroid ultrasound) (Fig. 2)

An acoustic shadow or enhancement is an ultrasound characteristic on thyroid ultrasound imaging. An acoustic shadow is a dark or black (anechoic) area behind bony structures or calcifications on ultrasound views of the neck. This is related to the inability of ultrasound waves to penetrate bony structures (or calcified areas), creating an area invisible by ultrasound behind the structure, appearing as a dark area behind the more light rim of hyperacustic areas.

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Figure 2. Artifacts on ultrasound. A, B - Thyroid nodules with eggshell type of calcifications around the nodule (arrow a). Artifacts on thyroid ultrasound: arrow "b" – comet tail; arrow "c" - acoustic shadow. A – thyroid ultrasound transverse view; B, C – thyroid ultrasound, longitudinal view.

Acute infectious thyroiditis

See Acute thyroiditis

Acute suppurative thyroiditis

See Acute thyroiditis

Acute thyroiditis

(see Acute infectious thyroiditis, Microbial inflammatory thyroiditis, Acute suppurative thyroiditis)

Acute thyroiditis or acute infectious thyroiditis is a rare bacterial or fungal infection of the thyroid gland that develops rapidly with acute symptoms. Those symptoms include painful thyroid glands and a fever, and they progress (get worse) rapidly. Acute infectious thyroiditis is more common among children but can affect adults as well. Staphylococcus aureus is the most common infectious agent. Acute thyroiditis may also develop into suppurative thyroiditis—a relatively rare condition caused by an infectious organism or bacterium that results in the progression of inflammation (acute thyroiditis) with the development of a pus.

Adequate fine needle aspiration (FNA) thyroid biopsy

Thyroid fine needle aspiration (FNA) biopsy is a gold standard of care tests to diagnose thyroid cancer in the thyroid nodule. In order to perform the evaluation of a biopsy sample, guidelines have been developed to help pathologists (cytopathologists) make informal decisions on the correct diagnosis of the sample, regardless of different practices across the world. This informal consensus was presented to pathologists as adequacy.

An adequate FNA thyroid biopsy specimen is a specimen that contains at least six groups of follicular cells (main group of thyroid cells) with ten to twenty cells in each group on two different slides. That means that even if the biopsy is performed in different hospitals across the country (or any part of the world), the description of the biopsy should always be based on adequacy. Sometimes the biopsy result will be reported as benign, but the sample adequacy will be reported as inadequate; that makes the benign diagnosis less reliable as compared to an adequate biopsy. In order for the FNA biopsy diagnosis to be reliable and accurate, at least one of several biopsy samples should be reported as adequate (it is not necessary that all samples would be called adequate).

Advanced disease

Advanced disease is defined by the progression (worsening) of the cancer to the point where the goal of treatment and care may not be cured, or where cure is not an option. Advanced disease can be managed (since there is no treatment possible in this case) by palliation or supportive therapy.

Agenesis, thyroid

Agenesis or athyreosis is the failure of the thyroid gland to develop due to a defect in survival of the thyroid follicular cell precursors. Thyroid aplasia is the total absence of thyroid gland in orthotopic (normal) locations and ectopic (outside of the normal) locations.

AGES thyroid cancer staging

AGES is the thyroid cancer staging system developed at the Mayo Clinic. It is based on (and stands for) age, grade, extent, and size (AGES): ≤4 low risk; >4 high risk.

Agranulocytosis

Agranulocytosis is a markedly decreased number of the white blood cells in the body. White blood cells are responsible for the immune response to infection. Decreasing the number of white blood cells that are responsible for the immune response may predispose the patient to the development of an infection. Symptoms of agranulocytosis are commonly associated with fever and/or sore throat.

Alcohol ablation therapy

(see Ethanol ablation or Percutaneous ethanol injection)

Alcohol ablation therapy is also called percutaneous ethanol injection (PEI). It is a treatment that uses ethanol injected locally within the thyroid nodule, cyst, or thyroid tumor. In the treatment of a thyroid cyst, injection of ethanol can be used to shrink large thyroid cysts (fluid-filled nodules). Ethanol ablation can be used to destroy recurrent thyroid cancer or metastatic thyroid cancer in lymph nodes without surgery. The latter is done in patients who are not good candidates for surgical therapy due to severe comorbidities.

Alimentary thyrotoxicosis

See Iatrogenic thyrotoxicosis or Thyrotoxicosis factitia

American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer (2015)

American Thyroid Association’s management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer (2015) was developed by the American Thyroid Association (ATA). The guidelines are evidence-based recommendations to inform clinicians, patients, researchers, and health policy makers on published evidence related to the diagnosis and management of thyroid nodules and differentiated thyroid cancer. Guidelines represent contemporary, optimal care for patients with thyroid cancer.

AMES

The AMES is a thyroid cancer staging system that was developed at the Lahey Clinic in the 1980s. It is based on prognostic factors including age, distant metastases, extrathyroidal invasion, and size. AMES stands for age, metastases, extent, and size.

Amiodarone

Amiodarone is a potent antiarrhythmic drug that is commonly used for the treatment of atrial fibrillation (irregular heart rhythms). Amiodarone is an iodine-based drug, with a pharmacological structure resembling the thyroid hormone thyroxine (T4). Since amiodarone contains iodine, it can cause thyroid problems, including both hypothyroidism and hyperthyroidism. This is due to amiodarone’s high iodine content and its direct toxic effect on the thyroid gland. Although amiodarone-associated thyroid dysfunction is usually mild and reversible by discontinuing the use of the drug (which is not always possible), it can be severe and life threatening. Amiodarone-induced thyrotoxicosis can be lethal (see Amiodarone-induced thyrotoxicosis (AIT)).

Amiodarone-induced thyroiditis

(see Amiodarone-induced thyrotoxicosis (AIT))

Amiodarone can produce thyroid abnormalities ranging from abnormal thyroid function testing (asymptomatic—without symptoms) to severe symptomatic hypothyroidism or hyperthyroidism. Amiodarone-induced thyrotoxicosis can be lethal.

Amiodarone-induced thyrotoxicosis (AIT)

Amiodarone-induced thyrotoxicosis (AIT) is an elevation of thyroid hormone levels that can occur as a result of excessive iodine from amiodarone, resulting in increased thyroid hormone production and secretion or destruction of the thyroid cells. Amiodarone can produce thyroid abnormalities ranging from abnormal thyroid function testing to overt hypothyroidism or hyperthyroidism.

These adverse effects may occur in patients with an underlying thyroid disease (AIT type 1) or without preexisting thyroid disease and an apparently normal thyroid gland (AIT type 2). AIT 1 is a true iodine-induced hyperthyroidism occurring in patients with an underlying thyroid autonomy while AIT 2 is a drug-induced destructive thyroiditis. In type 1, amiodarone-induced thyrotoxicosis (AIT 1) is an excessive synthesis of thyroid hormone that develops due to amiodarone-stimulated, iodine-induced production of thyroid hormone. In rare instances, AIT 2 is caused by amiodarone-induced inflammation of thyroid tissue, resulting in release of preformed thyroid hormones and a hyperthyroid state. Amiodarone-induced thyrotoxicosis (AIT) occurs in up to 6 percent of patients taking this medication in iodine-sufficient areas of the world and in up to 10 percent in iodine-deficient areas, such as parts of Europe.

Anaplastic thyroid carcinoma (ATC) (Fig. 3)

Anaplastic thyroid carcinoma (ATC), also known as undifferentiated thyroid carcinoma, is a rare, aggressive and most lethal type of cancer. It is one of the deadliest diseases worldwide and carries a very poor prognosis. It comprises less than 1% of all thyroid cancers and accounts for the majority of deaths from thyroid carcinoma. While the other 99% of thyroid cancer types have a better or excellent prognosis, anaplastic thyroid cancer is extremely aggressive. most often presented in people over the age of 60, with an average overall survival of less than six months. In up to half of cases, anaplastic thyroid cancer may arise from preexisting differentiated thyroid carcinomas. In contrast to all other types of thyroid cancer, most patients with anaplastic thyroid cancer die. It is composed of undifferentiated thyroid follicular cells and characterized by a rapid course of cancer growth with local invasion into surrounding vital neck structures, rapid metastatic spread to lymph nodes and distant organs. Diagnosis is usually made at a very late stage and more than half of the patients have distant metastasis at initial presentation. Treatment includes surgery, which is not effective in the vast majority of patients since at the time of the diagnosis the cancer has already spread, radiotherapy, and/or chemotherapy. Neither one of them have any significant impact on a cure either. The rarity and the rapid progression of ATC is a major barrier in finding effective therapies. Thus, the treatment that is the current standard of care for these patients is largely palliative, unless diagnosis is made in an earlier stage (as an incidental finding of a small thyroid tumor).

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Figure 3. Anaplastic thyroid carcinoma. Pathology slide, H&E staining, low power view, showing a group of undifferentiated cells with sarcomatoid (look like the cells of a sarcoma tumor) appearance that are characterized by spindle cells and giant cells.

Anaplastic thyroid carcinoma treatment

Anaplastic thyroid carcinoma has a very poor prognosis. All anaplastic thyroid cancers are considered to be stage IV. Surgical treatment is performed, when possible, in patients with cancer confined to the thyroid, which is almost never the case, due to rapid progression and the late diagnosis in the majority of the cases. The other treatment option includes external-beam radiation with or without chemotherapy. Patients with cancer that cannot be surgically removed and those with distant metastasis (spread) are usually treated non-surgically with palliative radiation and chemotherapy. Despite treatment, life expectancy is still very poor and the overall survival is less than six months, even with implementation of therapy.

Anemia

Anemia is a low blood cell count, specifically red blood cells which carry oxygen throughout the body to all cells. The most common symptom of anemia is fatigue.

Antibodies

Antibodies are proteins produced by the immune system (immune cells) that help defend the body against foreign invasion, hey attack and destroy bacteria, fungi, and viruses that cause infections. Occasionally the antibodies get confused and attack the body’s own tissues, causing autoimmune disease.

Antioxidants

Antioxidants are substances, or compounds, produced in the body or different types of foods. They prevent cell damage caused by oxidation in the body which has been linked to cancer and aging. Antioxidants help to defend cells from damage caused by potentially harmful molecules known as free radicals.

Antithyroglobulin antibodies (anti-TG antibodies)

Antithyroglobulin antibodies are antibodies directed against a protein called thyroglobulin. This protein is produced by the thyroid gland. Antithyroglobulin antibodies attack the body’s own thyroid gland instead of attacking bacteria and viruses. Antithyroglobulin antibody is a protein that is found in blood and produced by the body’s immune cells. They are signs of thyroid gland damage caused by the immune system and are markers for autoimmune thyroid disease. They are also found during Thyroiditis. Blood tests for anti-TG antibodies measure serum levels of antibodies. A positive test, showing the presence of antithyroglobulin antibodies, may be found in patients with Graves’ disease (overactive thyroid), autoimmune hypothyroidism such as Hashimoto thyroiditis (underactive thyroid), subacute thyroiditis, systemic lupus erythematosus, and Type 1 diabetes. This test may be positive in pregnant women, it has a strong familial presence, meaning it is not only found in the patient but their family members with autoimmune Thyroiditis.

Thyroglobulin is the major protein produced by functioning thyroid cells, both normal and cancerous. In patients with thyroid cancer, Thyroglobulin can be used as a cancer marker after all of the normal thyroid tissue is removed by a procedure called thyroidectomy and radioactive iodine therapy. Patients who are treated by a thyroidectomy for thyroid cancer should have undetectable or very low thyroglobulin levels. Therefore, anti-TG antibody level should be undetectable or should be going down after the surgery, if it was elevated prior to surgery. Blood thyroglobulin level is the major tool used to track the treatment and recurrence of thyroid cancer as well. The thyroglobulin level is generally directly related to the amount of cancer cells present in the body. A major limitation to this is the presence of anti-thyroglobulin antibodies which occur in ~25% of thyroid cancer patients. This often makes the thyroglobulin measurement inaccurate. Measuring thyroglobulin antibody levels after treatment for thyroid cancer can help detect thyroid cancer recurrence and to decide what is the best monitoring test to use and what treatment to implement. The presence or elevation of thyroglobulin level indicates persistent or recurrent disease. Anti-TG antibody can be used as a surrogate marker for the recurrent or persistent disease (cancer) as well. A negative test result means that there are no antibodies present in the blood, it is a normal result. Reappearance of antibodies after an initial undetectable level, or elevation of the antibody levels after they were found to be lowered, indicates that thyroid tissue or thyroid cancer recurred, or become bigger, and now is detectable by body’s immune system. This can be served as an additional marker for the recurrence of thyroid cancer.

These antibodies are easily detected in routine testing of patients, and when positive may indicate the presence of an autoimmune thyroid disease in patients with subclinical hypothyroidism, women with recurrent miscarriages, and patients with diagnosis of Graves’ disease. Detection of anti-TG antibodies help to predict which Graves’ patients can be weaned off antithyroid medications.

Antithyroid drugs

See Antithyroid medications

Antithyroid medications

Antithyroid medications block the thyroid from producing thyroid hormones (T3 and T4). Antithyroid agents prevent or suppress the biosynthesis of thyroid hormones. Antithyroid medications are used to treat Hyperthyroidism by inhibiting (preventing) the excessive production of thyroid hormones or by decreasing thyroid hormone activity. They decrease the peripheral (in the blood) conversion to a more active form of a thyroid hormone. Antithyroid medications are the initial most common treatment option for patients with hyperthyroidism, caused by Graves’ disease or toxic multinodular goiter. The goal of antithyroid therapy is to prevent the thyroid from producing excess amounts of thyroid hormone and cure symptoms of Hyperthyroidism. In the US, there are two antithyroid medications available: propylthiouracil (PTU) and methimazole (also known as Tapazole). The major difference between two is that PTU blocks the synthesis of thyroxine (T4) and triiodothyronine (T3) by thyroid follicular cells and also blocks peripheral (in blood) conversion of less active form of thyroid hormone, T4, into more active form of thyroid hormone, T3. Methimazole only blocks the synthesis of thyroxine (T4) and triiodothyronine (T3) by the thyroid gland. Methimazole is a newer medication, but it may cause severe birth defects if it is administered during the first trimester of the pregnancy. Therefore, it is recommended to stop Methimazole in the first trimester of pregnancy and replace it with PTU. There following options that are currently used to treat hyperthyroidism:

Methimazole (Northyx, Tapazole)

Propylthiouracil (PropylThiouracil, PTU)

Potassium iodide (SSKI, ThyroSafe, ThyroShield, iOSAT) (see Potassium iodine or SSKI)

Sodium iodide 131I (Iodotope, Hicon)

Antithyroid peroxidase antibodies

(the same as TPO antibodies, or Thyroid peroxidase antibodies)

TPO antibodies are produced by the immune system and attack the thyroid cells, instead of attacking bacteria and viruses. TPO antibodies are a marker for autoimmune thyroid disease, which is the main underlying cause for hypothyroidism (Hashimoto disease, also known as Hashimoto thyroiditis) and hyperthyroidism (Graves’ disease, hyperthyroidism).

Anti-TSH receptor antibodies (the same as TSH antibodies, TSR receptor antibodies)

Autoantibodies fight against the thyroid-stimulating hormone (TSH) receptor. Anti-thyroid stimulating hormone receptor antibodies are pathophysiologic and clinical indicators of autoimmune thyroid diseases, such Graves’ disease. They are capable of activating or blocking TSH receptor functions, to the TSH receptor found on the thyroid follicular cells. They mimic a normal TSH molecule and stimulate this receptor that results in thyroid follicular cells to produce a high amount of thyroid hormones resulting in hyperthyroidism.

Aplasia

See Thyroid aplasia

Armour Thyroid

Armour Thyroid is a desiccated (dried up) thyroid extract of thyroid hormone from animal thyroid glands. Currently, desiccated thyroid extract is made from pig thyroids and is available as Armour Thyroid™ and Nature-Thyroid™.

Artery (thyroid artery, inferior thyroid artery)

The arteries are blood vessels that deliver oxygen-rich blood from the heart to the tissues of the body, in this case the thyroid gland. This is how the thyroid gland, just like any other gland in the body, remains functional.

Artifacts on ultrasound (see Fig. 2)

An Artifact is a finding that does not correspond to a real structure but is related to the views that are created by reflection of the ultrasound waves. One example is comet-tail artifacts, a hyperechoic line often seen in colloidal cysts. This appears as a calcification, but it is not a real structure, and not a calcification (made from calcium). Comet-tail is considered a marker for benign finding that is different from a calcification. The following are ultrasound artifacts: tangential artifact, echo-free zone, acoustic enhancement (enhancement artifact), reverberation artifact (repetitive cycle losing energy each time). Acoustic enhancement (enhancement artifact) is the area behind the cyst that is brighter (almost white) than the dark-colored cyst because ultrasound waves pass through the cyst readily (see acoustic shadow). Trachea can cause artifacts as mirror artifacts with internal reflection.

ATA (American Thyroid Association)

The American Thyroid Association (ATA) is the leading worldwide organization dedicated to the advancement, understanding, prevention, diagnosis, and treatment of thyroid disorders and thyroid cancer. Founded in 1923, ATA is an international membership medical society with over 1,700 members from 43 countries around the world.

Ataxia-telangiectasia syndrome

Ataxia-telangiectasia is a rare autosomal-recessive disorder (see autosomal-recessive disorder) caused by mutations in the ataxia-telangiectasia mutated (ATM) gene. Ataxia-telangiectasia is characterized by early-onset progressive cerebellar ataxia, apraxia of eye movements, oculo-cutaneous telangiectasia, the absence or rudimentary appearance of a thymus, immunodeficiency, lymphoid tumors, insulin-resistant diabetes, and radiosensitivity. Very rarely is it associated with development of papillary and follicular thyroid cancers.

Athyreosis

Athyreosis, or agenesis, is the failure of the thyroid gland to develop due to a defect in survival of the thyroid follicular cell precursors.

Atrophic thyroiditis

Atrophic thyroiditis is an autoimmune disease of the thyroid gland characterized by the presence of thyroid autoantibodies that attack