Thyroid Flashcards
What is the anterior triangle?
The anterior triangle is an inverted triangle with its base above and the apex pointing downwards at the manubrium of the sternum. It can be further subdivided into smaller triangles by the crossing of digastric and omohyoid muscles.
What are the boundaries of the anterior triangle?
anterior: median line of the neck
posterior: anterior margin of sternocleidomastoid
base: inferior border of the mandible , which is a line from the inferior border of the mandible to the mastoid process.
the roof of platysma muscle and subcutaneous tissues;
the floor, formed by the pharynx, larynx and thyroid gland;
the apex which is the jugular notch; and
What is contained in the anterior triangle?
The anterior triangle contains glandular structures (such as the thyroid and parathyroid glands) and lymphatics. The carotid triangle in particular contains the carotid vessels and associated veins and nerves.
What are the subdivisions of the anterior triangle?
digastric (submandibular) triangle
muscular triangle
carotid triangle
submental triangle (half, only because there is only one submental triangle)
What is the posterior triangle?
The posterior triangle of the neck forms the posterior compartment of the neck and is separated from the anterior triangle by the sternocleidomastoid muscle
What are the boundaries of the posterior triangle?
anterior: posterior border of sternocleidomastoid
posterior: anterior border of trapezius
inferior: middle third of the clavicle
roof: skin, superficial fascia and the investing layer of deep cervical fascia
floor: prevertebral fascia overlying splenius capitis, semispinalis capitis, levator scapulae, scalenus medius and scalenus anterior
What are the contents of the posterior triangle?
The posterior triangle contains mostly vessels and nerves that connect the neck and the upper limb. It also contains superficial and deep lymph nodes.
Describe a pyramidal lobe
A pyramidal lobe (Lalouette’s pyramid) may be seen in 10-40 percent of cases, extending upward from the isthmus or the left lobe to the suprahyoid region.
Describe the posterior thyroid
The posterior part of the gland is attached to the cricoid cartilage by a ligamentous band (ligament of berry).
What is the normal size of an adult thyroid?
Normally L5.0cm, W3cm, D2cm, isthmus 2-3mm thick; thyroid gland weighs about 20-30g in the adult. It can fluctuate with age and pregnancy
Describe the vascularity of the thyroid?
Each lobe generally has two arteries (superior and inferior thyroid arteries) and three veins (superior, inferior and medial) that originate from a peri-thyroid plexus
Where do thyroid nerves derve from?
Superior, middle and inferior cervical ganglia
What are the parathyroid glands?
Parathyroid glands, usually two pairs of each superior and inferior, lie close to the posterior surface of the thyroid gland with many variations in number and position
Describe the embryological development of the neck.
The thyroid is the first endocrine gland to form in the embryo and appears in the 4th embryonic week as median endodermal thickening in the primitive pharynx which forms the thyroid diverticulum. The thyroid is derived from the thyroid diverticulum in the floor of the primitive pharynx. It descends from the base of the tongue to the base of the neck along the thyroglossal duct. The thyroid continues to descend until it reaches just inferior to the cricoid cartilage by the 7th week. Three pairs of salivary glands arise from the pharyngeal region.
What is the normal final remnant of the thyroglossal duct?
foramen caecum of the tongue
What are thyroid follicular cells made up of?
Follicles are largely made up of simple cuboidal epithelial cells that are referred to as follicular cells and produce the glycoprotein, thyroglobulin.
The role of thyroid follicular epithelial cells is to convert thyroglobulin into T4 and T3.
What is the role of parafollicular cells?
Parafollicular cells, or C cells, can also be found in the follicular epithelium as seen in They secrete the hormone calcitonin which controls calcium metabolism.
Describe the fibrous capsule of the thyroid
A thin fibrous capsule surrounds the thyroid and sends septa into the gland dividing it into lobules made up of 20-40 evenly dispersed follicles.
Surrounding the fibrous capsule is a loose sheath formed by the visceral part of the pretracheal deep cervical fascia.
What are the symptoms of thyroid gland enlargement?
Obstruction, difficulty swallowing (dysphagia), compression of large blood vessels, lymphatics and nerves in the neck and upper thorax, sensation of tightness or pain in the anterior neck, discomfort when swallowing, compression of blood vessels may inhibit the return of blood from the neck and head and may even result in superior vena cava syndrome.
What are symptoms of malignant enlargement?
Pain, hoarseness of the voice if laryngeal nerves are affected, coughing up of blood if the trachea is invaded
Describe the superior parathyroid glands.
arise from the paired fourth branchial pouches (clefts), along with the lateral lobes of the thyroid gland
Minimal migration occurs during fetal development
remain associated with the posterior aspect of the middle to upper portion of the thyroid gland.
Describe the inferior parathyroid glands
arise from the paired third branchial pouches, along with the thymus
Both migrate caudally along with the thymus.
Making them more variable in location than the superior glands
Located anywhere from the angle of the mandible to the pericardium.
majority (>60%) come to rest at or just inferior to the posterior aspect of the lower pole of the thyroid.
What is the role of the thyroid gland?
The thyroid is an endocrine gland that maintains body metabolism and growth development by synthesising, storing and secreting thyroid hormones. Parafollicular cells (C-cells) make up a small amount of the thyroid gland composition, occurring mainly in small clusters between follicles. Parafollicular cells produce the hormone calcitonin which is involved in calcium homeostasis, decreasing the release of calcium from the bone to lower blood calcium levels.
What is the role of the parathyroids?
The parathyroids synthesise the hormone parathormone (PTH)
who’s role (along with vitamin D and calcitonin) is to maintain blood calcium levels.
In bone- increased reabsorption to mobilise calcium and phosphate (increases levels of P and Ca in the blood).
In the kidneys, increased tubular reabsorption of calcium and tubular secretion of phosphate (increases Ca in the blood and P in the urine).
In the gut, increased absorption of dietary calcium, magnesium and phosphate and reduced loss of calcium in faeces. (increases Ca and P in blood)
What does a rise in blood calcium do to parathyroid secretion?
A rise in blood calcium depressed parathyroid secretion while a fall increases it.
What are advantages of an FNA of the thyroid?
minimal materials (usually a very simply procedure) inexpensive quickly performed local anaesthetic often not used minimal discomfort (usually) small bruise only (usually)
What are disadvantages of an FNA of the thyroid?
sample may be inadequate ( reduced if pathologist is present to check sample )
false positive/false negative/equivocal aspirates
dependence of cytopathology expertise
specific tissue-related potential pitfalls.
What are advantages of a thyroid core biopsy?
inexpensive
relatively atraumatic
may obviate the need for open biopsy
higher diagnostic yield (though there is some varying opinion about this)
What are disadvantages of a thyroid core biopsy?
greater chance of local haemorrhage due to larger bore needle used
tracheal perforation and other complications as there is probably reduced control of the needle depth with this procedure compared to FNA.
potential for facial nerve damage
possibility of tumour seeding, but very little evidence.
What is hyperthyroidism?
Hyperthyroidism is due to excessive secretion of thyroid hormones T3 and T4, often termed thyrotoxicosis.
What are causes of hyperthyroidism?
Graves’ disease
idiopathic nodular hyperplasia of the thyroid (toxic goitre)
tumours, such as hyperfunctioning thyroid adenoma and metastatic thyroid carcinoma
subacute or acute thyroiditis
choriocarcinoma or hydatidiform mole
overdose of thyroid hormone
What are symptoms are hyperthyroidism?
mostly related to the abnormally high metabolic rate warm and sweaty increased pulse rate and blood pressure Tachycardia Tremor muscle weakness weight loss Restlessness Anxiety Amenorrheoa and exophthalmos may also occur, especially in Graves' disease.
What is treatment for hyperthyroidism?
Treatment is often with anti-thyroid drugs for Graves’ disease. If this is not effective or the cause is due to tumour or nodular hyperplasia, then a subtotal thyroidectomy is usually performed.
What is hypothyroidism?
Hypothyroidism occurs due to reduced circulating thyroid hormones. This usually results from a functional failure of the thyroid gland.
What are causes mof hypothyroidism?
developmental defects, such as congenital thyroid aplasia
postoperative thyroidectomy, for example, after removal of tumour
thyroiditis, often autoimmune such as Hashimoto’s thyroiditis
iodine deficiency where dietary iodine is low
deficiency of TRH from the hypothalamus
What are symptoms of hypothyroidism?
Usually related to a low metabolic rate Low BMR Bradycardia Shortness of breath Lethargy Mental sluggishness Weight gain Constipation Cold sensitivity Cretinism occurs in utero or infancy usually due to congenital aplasia. It will result in mental and physical retardation unless detected and treated with thyroid hormones. This is usually a routine test for all newborns
What is treatment of hypothyroidism?
Standard treatment for hypothyroidism involves daily use of the synthetic thyroid hormone
What is hyperparathyroidism?
Excessive secretion of parathormone is termed hyperparathyroidism. This causes hypercalcemia.
How does hyperparathyroidism cause hypercalcemia?
bone reabsorption and calcium mobilisation from the skeleton, which can cause the bone to be very susceptible to fracture
increased renal tubular reabsorption and retention of calcium
enhanced gastrointestinal calcium absorption
What are causes of hyperparathyroidism?
Primary - parathyroid adenoma (80-90%) - hyperplasia (10-20%) - carcinoma (less than 1%) Secondary - associated with renal failure and vitamin D deficiency
What are the causes of multigland enlargement?
Multigland enlargement most often results from primary parathyroid hyperplasia and less often from multiple adenomas.
What are symptoms of multigland enlargement?
- elevated serum calcium
- Hypophosphatasia
- hypercalciuria
- possible nephrocalcinonsis or renal calculi
- possible bone deformities in severe cases
What is the treatment for multigland enlargement?
Remove one or more of the glands.
What are risk factors for multigland enlargement?
- Most cases are sporadic
- Prior external neck radiation (small amount of cases)
- Long term lithium therapy
- Hereditary (multiple endocrine neoplasia syndrome (MEN I))
- Familial syndromes such as familial hypocalciuric hypercalcemia
What is the prevalence of primary hyperparathyroidism?
- common endocrine disease 1 to 2 per 1000 population.
- Women are affected 2-3:1 particularly after menopause.
- Most >50 years
- rare <20 years
What kind of laboratory results would you expect to see in primary hyperparathyroidism?
- elevated serum calcium
- Hypophosphatasia
- Hypercalciuria
- PTH level that is “inappropriately high” for the corresponding serum calcium level confirms the diagnosis
