15b Disease of the Parathyroid Gland Flashcards
What is the embryology of the parathyroid glands?
What is the embryology of the parathyroid glands?
The superior parathyroid glands develop from the fourth branchial pouch and the inferior parathyroid gland develops from the third pharyngeal pouch along with the thymus. Although most people have four parathyroid glands, 3% to 7% have five to seven glands, and 3% to 5% have fewer than four glands.
What are the normal characteristics of parathyroid glands?
What are the normal characteristics of parathyroid glands?
The average parathyroid gland weighs 35 to 50 mgs and is 1 to 5 mm in diameter. Its primary blood supply is from the inferior thyroid artery, or more rarely from the posterior branch of the superior thyroid artery.
What is primary hyperparathyroidism?
What is primary hyperparathyroidism?
Primary hyperparathyroidism is caused by the overproduction of PTH. Etiology is usually due to:
- Solitary parathyroid adenoma (85%)
- Multiple hyperplastic glands (10% to 15%)
- Multiple adenomas (3% to 4%)
- Parathyroid carcinoma (<1%)
Primary hyperparathyroidism may be related to overexpression of PRAD1 oncogene or low-dose radiation exposure, but the true etiology is unknown.
What are secondary and tertiary hyperparathyroidism?
What are secondary and tertiary hyperparathyroidism?
Secondary hyperparathyroidism is seen in patients with chronic renal failure causing elevated phosphate and decreased 1-alpha-hydroxylase in the kidney resulting in low vitamin D. It is associated with mild hypercalcemia but high PTH. Surgery is recommended for osteopenia and is usually a sub-total (three and one half glands) parathyroidectomy. Tertiary hyperparathyroidism is the result of long-term secondary hyperparathyroidism that results in autonomous parathyroid function, even when the underlying causes are corrected. Cinacalcet (calcimimetic agent) can be effective in treating patients with secondary hyperparathyroidism.
What are the classic symptoms of hypercalcemia?
What are the classic symptoms of hypercalcemia?
“Moans, groans, stones, and psychic overtones”: the most common symptoms include GI disturbance (nausea, constipation, peptic ulcer, pancreatitis), muscle weakness, renal stones, hypertension, cardiac arrhythmia, polydipsia, and neuropsychiatric symptoms including depression, fatigue, and memory loss. Renal stones and bone disorders such as osteitis fibrosa cystica are rare since the advent of routine parathyroid hormone (PTH) testing.
What is the differential diagnosis for hypercalcemia?
see table
How is the diagnosis of primary hyperparathyroidism made?
How is the diagnosis of primary hyperparathyroidism made?
- Increased serum total calcium and increased or very high PTH.
- Serum phosphate is decreased or low-normal.
- If PTH is elevated but serum calcium is normal or low normal, rule out vitamin D insufficiency or malabsorption.
- If both calcium and phosphate levels are elevated, rule out hypervitaminosis D.
What are available localization imaging studies for primary hyperparathyroidism?
What are available localization imaging studies for primary hyperparathyroidism?
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Noninvasive Localization
- Technetium 99m sestamibi (Tc99m MIBI): Sestamibi localizes into the mitochondria of parathyroid cells. Late phase images at 2 hours allows for sestamibi to clear from the thyroid gland, but not the parathyroid. Single adenoma detection is high with sensitivity of 100% and specificity of 90%. Less useful for four-gland hyperplasia.
- Tc 99m MIBI plus single photon emission CT (SPECT): Addition of SPECT gives a higher resolution three-dimensional image and some report superior detection of adenomas within the carotid sheath or mediastinum.
- Tc 99m + thallium 201 subtraction: Thallium is taken up by the parathyroid and less by the thyroid gland. Subsequent subtraction image can detect enlarged parathyroid glands. Sensitivity rates are varied (30% to 90%), but more widely available than MIBI.
- Ultrasound: Superior than other techniques for identifying intrathyroid parathyroid adenomas, quicker, and involves no radiation. Ectopic adenomas of retroesophageal, trachea and mediastinum are more difficult to localize with US. False positive rate is 15% to 20%.
- MRI: Adenomas appear with high signal intensity on T-2 weighted images. May be useful in identifying ectopic adenomas and in patients requiring re-exploration after initial surgery.
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Invasive Localization
- Intraoperative gamma probe: Tc 99m MIBI is injected 2 hours prior to surgery and radioactive parathyroid glands are localized using handheld gamma probes.
- Parathyroid angiography/arteriography.
- Venous sampling of PTH: Angiographic sampling of selective veins preferred, but even large vein sampling (internal jugular vein) can help lateralize the gland and can be useful in re-exploration.
- US guided parathyroid fine needle aspiration (FNA).
What are the most common ectopic locations of parathyroid glands?
What are the most common ectopic locations of parathyroid glands?
Ectopic parathyroid glands can be found in the superior mediastinum, thymic capsule, retro-esophagus, within the carotid sheath, and medial to the superior thyroid pole. The inferior parathyroid gland has more variability in its final location because it descends with the thymus gland. The superior parathyroid gland tends to be more closely associated with the lateral lobe of the thyroid.
What is the most recent recommendation for surgery in the asymptomatic primary hyperparathyroid patient?
see table
How is intraoperative PTH monitoring used in parathyroid surgery?
How is intraoperative PTH monitoring used in parathyroid surgery?
PTH has a half-life of 3 to 5 minutes. In parathyroid surgery, the goal is to see a decrease in PTH level by more that 50% at 10 minutes after removal of a parathyroid adenoma or hyperplasia. Intraoperative PTH monitoring allows focused parathyroid surgery (i.e., one-gland surgery) and can prevent unnecessary bilateral four-gland exploration.
How is autotransplantation of parathyroid tissue performed?
How is autotransplantation of parathyroid tissue performed?
Parathyroid tissue can either be autotransplanted at the time of surgery or cryopreserved for up to 18 months and transplanted at a later date. Transplantation occurs most commonly into the sternocleidomastoid (SCM) of the neck or into the brachioradialis of the arm. Transplanted parathyroid tissue usually functions within 3 months and has a success rate of 50%. One advantage of transplanting into the arm is the ability to remove parathyroid tissue under local anesthetic if it becomes hyperplastic.
What are the surgical options for hyperparathyroidism?
What are the surgical options for hyperparathyroidism?
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Single gland disease plus positive MIBI scan
- directed unilateral exploration with intraoperative PTH monitoring to assess adequacy of resection
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MEN syndrome
- bilateral cervical exploration and four-gland identification
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Negative MIBI scan
- bilateral exploration with selective biopsy of suspicious glands and intraoperative PTH monitoring to assess adequacy of resection
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Secondary or tertiary hyperparathyroidism
- 3-1/2 gland resection or total parathyroidectomy with possible autotransplantation or cryopreservation of parathyroid tissue
What strategies are used for parathyroid re-exploration?
What strategies are used for parathyroid re-exploration?
In re-exploration, the strategy is to dissect lateral to medial, from the SCM to retroesophageal tissue overlying the cervical spine. Inferiorly, the thymus is resected. Medially, the prevertebral space (retroesophageal, retropharyngeal) is explored. The thyroid lobe is mobilized and palpated for an intrathyroid parathyroid. The carotid sheath is opened from hyoid to mediastinum. If unilateral exploration is negative, contralateral exploration is then performed. Mediastinal exploration should be performed only after imaging (i.e., MIBI and MRI) has been done.
