Parathyroid

Question 1

Parathyroid Hormone

Answer 1

• A peptide hormone that increases plasma calcium
• Causes increase in plasma calcium by:

1. Mobilization of calcium from bone
2. Enhancing renal reabsorption 3.Increasing intestinal absorption (indirect)

Question 2

Hyperparathyroidism

Answer 2

Primary
Primary hyperparathyroidism results from a hyperfunction of the parathyroid glands themselves. There is over secretion of PTH due to adenoma, hyperplasia or, rarely, carcinoma of the parathyroid glands.

Secondary
Secondary hyperparathyroidism is the reaction of the parathyroid glands to a hypocalcemia caused by something other than a parathyroid pathology, e.g. chronic renal failure.

Tertiary
Tertiary hyperparathyroidism result from hyperplasia of the parathyroid glands and a loss of response to serum calcium levels. This disorder is most often seen in patients with chronic renal failure and is an autonomous activity.

Question 3

Signs and symptoms

Answer 3

Weakness and fatigue Depression
Bone pain
Muscle soreness (myalgias) Decreased appetite
Nausea and vomiting, constipation Polyuria, polydipsia
Cognitive impairment
Kidney stones
Osteoporosis

Question 4

Embryology

Answer 4

• The upper 2 parathyroids come from the fourth branchial pouch which also produces the thyroid gland.
• The lower 2 parathyroids come from the third brachial pouch which is also responsible for producing the thymus gland The thymus eventually sits behind the breast bone (sternum).

Question 5

Parathyroid glands and adenomas

Answer 5

Parathyroid adenomas are usually found in the inferior parathyroid gland; however, in 6%-10% of patients, they may be located in
• the thyroid,
• thymus,
• the pericardium,
• or behind the oesophagus

Question 6

Why image parathyroid glands?

Answer 6

To detect and localise hyper-functioning parathyroid tissue (parathyroid adenomas and parathyroid hyperplasia) in primary parathyroidism

Also used to localise hyper-functioning parathyroid tissue in patients with recurrent or persistent disease.

It is crucial that parathyroid glands are accurately localised prior to surgery – the success rate of this type of surgery is quite ‘liquid’.

Question 7

Treatment

Answer 7

Surgery

Location and exact number of glands is extremely variable.

Normal and diseased glands are often very small.

Parathyroid surgery is time consuming, technically difficult and requires considerable experience. Requires thorough bilateral neck dissection to locate all 4 glands. If no tumour or hyperplasia is found, a search for ectopic glands is undertaken (could involve sternotomy).

There is still a 5% surgical failure rate (recurrence rate) for experienced surgeons. The main reason for this in experienced surgeons, is the failure to locate multiple ectopic or supernumerary abnormal glands.

Question 8

Primary hyperparathyroidism Pathology of lesions

Answer 8

SINGLE ADENOMAS 95% 300-5000 mg

Adenomas Multiple 1.5%

Multi gland hyperplasia 3.5%

Carcinoma <1%

Question 9

Bilateral neck exploration was the standard surgical approach

Answer 9

Cure in 80-90% of patients

Surgical failure in 10-20% of patients

Question 10

Minimally invasive surgery

Answer 10

Benefits:
Small incision 3 to 4cm
Reduced operative time – 15 minutes LA
Day patient
Reduced morbidity -- recurrent laryngeal nerve injury, hypocalcaemia

Question 11

Imaging modalities for the preoperative identification of the site of an adenoma

Answer 11

Ultrasound Sensitivity 70 %
CT Sensitivity 60 %
Parathyroid Study - Sensitivity 95 – 100 %

Question 12

Parathyroid imaging

Answer 12

• US
• NM scintigraphy
• CT• CT is commonly used in the setting of a failed parathyroidectomy for the detection of suspected ectopic glands.
• MRI
• MRI is infrequently utilized in initial work up because of lower spatial resolution and artifacts.

Question 13

Ultrasound for parathyroid

Answer 13

Ultrasound is one of most commonly used initial imaging modalities.
Nodules need to be > 1cm to be confidently seen on ultrasound
Parathyroid adenomas tend to be homogeneously hypoechoic to the overlying thyroid gland

Question 14

NM for parathyroid

Answer 14

Differential washout imaging
• Early and delayed (15 – 20 min and 2 hour post inj.) images are obtained after administration of 99mTc- MIBI.
• There is faster washout of MIBI from thyroid as compared to thyroid adenoma(s), as the adenomas are hyperactive and contain a greater number of mitochondria.

Subtraction imaging
• An image of the thyroid is obtained using low dose of 99mTcO4 or 123I.
• Followed by combined imaging of the thyroid and parathyroid glands using a high dose of 99mTc-MIBI
• The thyroid image is subtracted from the combined image.