THYROID

Anatomy:

• Consists of a right and a left lobe that lie over the deep structures of the neck  (close proximity to the larynx, trachea, parathyroid glands, and esophagus)
• Wraps around the trachea and located near the thyroid cartilage
• Anterior and medial to the carotid artery, jugular vein and the vagus nerve
• Lateral lobes approximately 5 cm in length and extend to the level of the midthyroid cartilage superiorley and the 6th tracheal ring inferiorly.  Thes lobes are connected to the isthmus at the level of the 2nd to 4th tracheal rings

Physiology:

• Produces several hormones
• Thyroxin – controls metabolism (metabolism – the rate at which food is converted to energy)   hypothyroidism is cause by an underproduction of thyroxin and hyperthyroidism is cause by and overproduction of thyroxin
• Thyrocalcitin – regulates calcium in the blood
• Triiodothyronine
• The thyroid is regulated by the pituitary & hypothalamic hormones via negative feedback
• The production of these hormones relies on the thyroid glands ability to remove IODINE from the blood.
• IODINE IS ESSENTIAL to the production of thyroid hormones

Disorders of the Thyroid:

Hypothyroidism: a glandular disorder resulting from insufficient production of thyroid hormones

• Children :  with hypothyroidsim will develop with a short stature, scant hair, cannot tolerate cold, mental retardation (cretinism)
• They are given synthroid
• Adults : with hypothyroidism will have weight gain ,goiter, lack of energy (Hoshimoto’s Disease
• Goiter - A noncancerous enlargement of the thyroid gland, visible as a swelling at the front of the neck, that is often associated with iodine deficiency

 

Hyperthyroidism : pathologically excessive production of thyroid hormones or the condition resulting from excessive production of thyroid hormones

• Graves Disease
• Causes tachycardia – rapid heartbeat
• They remove the thyroid then put patient on hormone therapy

Risk Factors:

• Therapeutic radiation – especially during infancy (this was done in the 1940’s and 50’s to treat benign disease)  25 year latency period
• Higher risk for females
• Mantle field for Hodskins also associated with higher risk
• Genetics – most medullary types are sporadic but some are hereditary as autosomal dominat with variable expression

Signs and Symptoms:

• Most are asymptomatic thyroid nodules
• Can feel pressure in the neck area
• Change in voice can be cancer or a goiter

Workup:

• Most nodules are benign
• Only 10% of nodules found are malignant
• Family history and personal history are important
• Sudden growth would be very suspicious (if there was a history of Head and Neck cancer)
• FNA (fine needle aspiration) is done first
• Ultrasound
• radionuclide studies are done with radioactive Iodine  (if nodules show up cold / nonfunctioning on scan they are more suspicious)
• Blood work is done : calcitonin would be elevated in medullary types
• CEA (carcinoembryonic antigen) is often elevated in medullary types
• Genetic testing : all individuals who inherit a particular mutation (called RET) will get thyroid cancer (medullary type) so the gland is removed in childhood

Clinical Presentation :

• most patients have a palpable neck mass
• 25% of young people with differentiated thyroid carcinoma present because of palpable cervical lymph node metastisis As a result of occult primary thyroid cancer

• Take a biopsy on persistant enlarged lymph nodes
• Lesions should become suspicious if they are:
• Hard
• Fixed
• And patientr displays hoarsness

Lymphatic Drainage:

• internal jugular chain
• delphian node
• pretracheal node
• paratracheal node
• Superior Mediastinal lymphatics

Pathology:

4 Malignant Thyroid Neoplasms:

1. papillary and mixed papillary- follicular
2. follicular
3. medullary
4. anaplastic

Papillary and Mixed Papillary Cancers:

• most common > 33-73% of all malignant thyroid lesions
• arise from the follicles that are most unilateral
• slow growing
• non-aggressive
• excellent prognosis
• 2-4 times more common in women
• peak in 3rd – 5th decades of life (but can occur at any age)
• 15 yrs and younger papillary carcinoma accounts for 80%
• can invade lymphatics but organ mets are rare
• usually treated with surgery (lobectomy or thyroidectomy)

Lymph spread:

• mets to regional lymph nodes through lymphatic channels
• at time of operation 50-70% already have vervical lymph node mets
• Delphian Node is sometimes biopsied

Surgery:

• rarely invasive
• seldom require the resection of the muscles of the neck, interjugular vein, esophagus, or trachea.
• Radical neck dissections, only if nodes are grossly involved with metastisis
• Special care when resecting with recurrant laryngeal, vagus, spinal accessory, and phrenic nerves.
• Preserve parathyroid

Follicular Carcinoma

• 14-33% of all thyroid cancers (less common that papillary and mixed papillary)
• also has a slightly poorer prognosis
• Tumors have greatest propensity to concentrate I-131
• 2-3 times more common in women
• 50-59 yrs old
• rare in children
• can produce metastisis
• Hurthle Cell – is a variant of follicular and has a worse outcome

Lymph spread:

• invades vascular channels
• metastisis  Hematogenously to distant sites including: bone, lung, liver, brain
• lymph nodes metastisis is uncommon

Medullary Thyroid

• 5-10% of thyroid cancers
• originates from the parafollicular cells and secretes calcitonin
• 80% appear spontaneously
• 20% occurring as part of familial multiple endocrine neoplasia syndromes
• hereditary type (autosomal dominant)
• highly curable if caught early
• no gender differentiation
• 5th decade on in age
• WORSE PROGNOSIS THAN PAPILLAR, PAPILLARY-FOLLICULAR, and FOLLICULAR, but better prognosis than anaplastic
• Spreads to lymph and can produce distant metastisis to lungs, liver, bone and adreneal glands
• Can be treated with thyroidectomy

Lymph spread:

• can vary from indolent to rapidly fatal growth patterns
• spreads regionally before displaying metastisis
• 50% of patients have regional metastisis At time of diagnosis
• metastisis occur hematogenously and through lymphatic route involving cervical nodes, lung, liver, and bone

Anaplastic Carcinoma

• worst overall prognosis
• more aggressive both locally and to distant organs in the patient
• high grade with rapid proliferation and invasion of both lymph and blood vessels
• short life expectancy (patient usually dies from local spread)
• 10% of all malignant thyroid lesions
• 40-90 yrs of age
• 4-1 women to men

Lymph spread:

• local invasion of structures (such as trachea)
• skin invasion (dermal lymphatic metastisis on the chest and abdominal walls)
• regional neck nodes can have involvement, although often hard to asses.

Rare Types of Thyroid Cancer: lymphomas, teratomas, sarcomas, Squamous cell

Treatment Principles :

Important for the physician to differentiate between benign and malignant

Surgery is common for most malignant tumors (fine needle aspiration)

• Differentiated types is treated with total thyroidectomy or lobectomy
• Medullary are usually treated with thyroidectomy and node sampling (possible neck dissection)
• Anaplastic : trachestomy is usually required. Patient is put on radiation and chemotherapy
• Cannot be surgically removed because of seeding
• We usually treat to reduce obstruction of airway (palliative)
• 60 Gy to a mini mantle type field
• RAI – 131   - radioactive iodine is also used
• Post op ablation of normal residual thyroid tissue after surgery or residual disease

External Beam Radiation Therapy:

• Used for unresectable cancer (Dose is 60 – 65 Gy in 6 – 6.5 weeks)

• In undifferentiated types EBRT is used for residual or recurrent disease (50 – 60 GY)
• Bone Metatsisis are given I 131 plus EBRT of 40 – 50 GY
• Meduallry EBRT is used for residual disease or extensive lymph node metasitisis (50 Gy in 5 weeks)
• Anaplastic EBRT slows but does not cure (60 – 65 Gy)
• Chemotherapy is only effectrive in anaplastic

Field Arrangment:

• entire thyroid gland, neck and superior mediastenum
• AP/PA, Obliques, or oppsed oblique portals

Prognosis:

• age
• gender
• histologic subtype
• capsular invasion

• Lesions confined to the gland  have an overall better prognosis than those demonstrating capsular invasion

• Patients with well-differentiated thyroid carcinoma (papillary and follicular) have a better prognosis than thise with undifferentiated carcinoma (anaplastic)

RAI – radioactive iodine

• can be ingested to find out if patient has mets
• can be used to kill mets (abalate)
• also can be used to kill remaining thyroid tissue