Parathyroid Flashcards
How many parathyroid glands are there?
Usually 4
What percentage of patients have 5 parathyroid glands?
5%
What percentage of patients have 3 parathyroid glands?
10%
What is the usual position of the inferior parathyroid glands?
Posterior and lateral behind the thyroid and below the inferior thyroid artery
What is the most common site of an extra parathyroid gland?
Thymus gland
What percentage of patients have a parathyroid gland in the mediastinum?
1%
If only 3 parathyroid glands are found at surgery, where can the 4th one be hiding?
Thyroid gland, thymus, mediastinum, carotid sheath, tracheoesophageal groove, behind the esophagus
What is the embryologic origin of the superior parathyroid glands?
4th pharyngeal pouch
What is the embryologic origin of the inferior parathyroid glands?
3rd pharyngeal pouch
What supplies blood to the parathyroid glands?
Inferior thyroid artery
What percentage of patients have all 4 parathyroid glands supplied by the inferior thyroid arteries exclusively?
80%
What is DiGeorge’s syndrome?
Congenital absence of the parathyroid glands and the thymus
What is the most common cause of hypercalcemia in hospitalized patients?
Cancer
What is the most common cause of hypercalcemia in outpatients?
Hyperparathyroidism
What cell type produces PTH?
Chief cells
What are the major actions of PTH?
Increases blood calcium levels (takes from bone breakdown, GI absorption, increased resorption from kidney, excretion of phosphate by kidney)
Decreases serum phosphate
How does vitamin D work?
Increases intestinal absorption of calcium and phosphate
Where is calcium absorbed?
Duodenum and proximal jejunum
What is primary HPTH?
Increased secretion of PTH by parathyroid glands.
Marked by elevated calcium, low phosphate.
What is secondary HPTH?
Increased serum PTH resulting from calcium wasting cause by renal failure or decreased GI calcium absorption, rickets or osteomalacia.
Calcium levels are usually low.
What is tertiary HPTH?
Persistent HPTH after correction of secondary HPTH.
Results from autonomous PTH secretion not responsive to the normal negative feedback due to elevated Ca levels.
What are the methods of imaging the parathyroid glands?
Surgical operation, U/S, Sestamibi scan, TI-201 (technetium)-thallium subtraction scan, CT, MRI, A-gram, venous sampling for PTH
What are the indications for a localizing preoperative study of the parathyroid glands?
Reoperation for recurrent HPTH
What is the most common cause of primary HPTH?
Adenoma
What are the etiologies of primary HPTH and percentages?
Adenoma (85%), hyperplasia (10%), carcinoma (1%)
What is the incidence of primary HPTH in the US?
1-4/4000
What are the risk factors for primary HPTH?
Family history, MEN-I and MEN-IIa, irradiation
What are the signs and symptoms of primary HPTH hypercalcemia?
Stones (kidney stones);
Bones (bone pain, pathologic fractures, subperiosteal resorption);
Groans (muscle pain and weakness, pancreatitis, gout, constipation);
Psychiatric overtones (depression, anorexia, anxiety)
Also: polydipsia, weight loss, HTN, polyuria, lethargy
What is the “33 to 1” rule?
Most patients with primary HPTH have a ratio of serum chloride to phosphate > 33
What plain x-ray findings are classic for HPTH?
Subperiosteal bone resorption (usually in hand digits)
How is primary HPTH diagnosed?
Labs (elevated PTH, hypercalcemia, hypophosphatemia, hyperchloremia).
Urine calcium should be checked for familial hypocalciuric hypercalcemia.
What is familial hypocalciuric hypercalcemia?
AD inheritance of a condition of asymptomatic hypercalcemia and low urine calcium, with or without elevated PTH.
In contrast, hypercalcemia from HPTH results in high levels of urine calcium.
What percentage of parathyroid adenomas are not single but found in more than one gland?
5%
What is the initial medical treatment of primary HPTH hypercalcemia?
IV fluids, furosemide
What is the definitive treatment of primary HPTH resulting from hyperplasia?
Neck exploration removing all parathyroid glands and leaving at least 30 mg of parathyroid tissue placed in the forearm muscles
What is the definitive treatment of primary HPTH resulting from parathyroid adenoma?
Surgically remove adenoma (send for frozen section) and biopsy all abnormally enlarged parathyroid glands (some experts biopsy all glands)
What is the definitive treatment of primary HPTH resulting from parathyroid carcinoma?
Remove carcinoma, ipsilateral thyroid lobe, and all enlarged lymph nodes (modified radical neck dissection for LN metastases)
What is the definitive treatment of secondary HPTH?
Correct calcium and phosphate.
Perform renal transplantation (no role for parathyroid surgery)
What is the definitive treatment of tertiary HPTH?
Correct calcium and phosphate.
Perform surgical operation to remove all parathyroid glands and reimplant 30-40 mg in the forearm if refractory to medical treatment.
Why place 30-40 mg of sliced parathyroid gland in the forearm?
To retain parathyroid function.
If HPTH recurs, remove some of the parathyroid gland from the easily accessible forearm.
What must be ruled out in the patient with HPTH from hyperplasia?
MEN-I and MEN-IIa
What carcinomas are commonly associated with hypercalcemia?
Breast cancer metastases, prostate cancer, kidney cancer, liver cancer, pancreatic cancer, multiple myeloma
What is the most likely diagnosis if a patient has a palpable neck mass, hypercalcemia, and elevated PTH?
Parathyroid carcinoma (vast majority of other causes of primary HPTH have non-palpable parathyroids)
What is parathyroid carcinoma?
Primary carcinoma of the parathyroid gland
What is the usual number of glands affected in parathyroid carcinoma?
1
What are the signs and symptoms of parathyroid carcinoma?
Hypercalcemia, elevated PTH, palpable parathyroid gland, pain in neck, recurrent laryngeal nerve paralysis (change in voice), hypercalcemic crisis
What is the common tumor marker for parathyroid carcinoma?
HCG
What is the treatment for parathyroid carcinoma?
Surgical resection of parathyroid mass with ipsilateral thyroid lobectomy, ipsilateral lymph node resection
What percentage of primary HPTH are caused by parathyroid carcinoma?
1%
What are the possible postoperative complications after a parathyroidectomy?
Recurrent nerve injury (unilateral: voice change, bilateral: airway obstruction); neck hematoma (open at bedside if breathing is compromised); hypocalcemia; superior laryngeal nerve injury
What is hungry bone syndrome?
Severe hypocalcemia seen after surgical correction of HPTH as chronically calcium-deprived bone aggressively absorbs calcium
What is the treatment of hypoparathyroidism?
Acute: IV calcium
Chronic: PO calcium, vitamin D
What is parathyromatosis?
Multiple small hyperfunctioning parathyroid tissue masses found over the neck and mediastinum.
Thought to be from congenital rests or spillage during surgery.
