The parathyroid glands Ass prof dr Asaad Mohammed

The parathyroid glands Ass. prof dr. Asaad Mohammed kadhim Consultant General &laparoscopic Surgery

The parathyroid glands are beanshaped structures, about the size of a grain of rice, weighing around 30 -40 mg each. There are usually four in no. , with two on each side, and they lie on the posterior surface of the thyroid gland.

They are symmetrically arranged in 80% of cases, with the two superior (upper) parathyroids lying about 1 cm above the point where the inferior thyroid artery enters the thyroid. The two inferior (lower) parathyroids lie about 1 cm below this point, usually around the lower pole of the

Superior parathyroids are more rarely ectopic than inferior glands, having travelled a shorter distance during embryological life. However, superior parathyroids have been found as high as the level of the thyroid cartilage and even at the level of the hyoid bone, but usually if ectopic they are more likely to be retro-oesophageal or some other posterior location. Intrathyroidal parathyroids are more likely to be superior glands.

Inferior parathyroids are much more variable in position, although 60% will be around the lower pole of the thyroid. Ectopic locations can be anywhere from the angle of the mandible (jaw) all the way down into the chest as low as the pericardium (covering of the heart), including the carotid sheath. The most common ectopic location however, is in the thymus (or thyrothymic tract) in the upper chest, due to the

The sole purpose of the parathyroid glands is to control calcium within the blood in a very tight range between 8. 5 and 10. 5. In doing so, parathyroid glands also control how much calcium is in the bones, and therefore, how strong and dense the bones are. Although the parathyroid glands are intimately related to the thyroid gland anatomically, they have no related function.

Calcium is the primary element which causes muscles to contract. Calcium levels are also very important to the normal conduction of electrical currents along nerves. Knowing these two major functions of calcium helps explain why people can get a tingling sensation in their fingers or cramps in the muscles of their hands when calcium levels drop below 8. 5

Parathyroid hormone (PTH) has a very powerful influence on the cells of the bones which causes them to release their calcium into the bloodstream. Calcium is the main structural component of bones which give them their rigidity.

Under the presence of parathyroid hormone, bones will give up their calcium in an attempt to increase the blood level of calcium. Under normal conditions, this process is very highly tuned and the amount of calcium in our bones remains at a normal high level. Under the presence of too much parathyroid hormone, however, the bones will continue to release their calcium into the blood at a rate which is too high resulting in bones which have too little calcium. This condition is called osteopenia and osteoporosis

When bones are exposed to high levels of parathyroid hormone for several years they become brittle and much more prone to fractures. Another way in the parathyroid hormone acts to increase blood levels of calcium is through its influence on the intestines. Under the presence of parathyroid hormone the lining of the intestine becomes more efficient at absorbing calcium normally found in our diet

HYPERPARATHYROIDISM 1/PRIMARY 2/SECONDARY

Primary hyperparathyroidism (PHPT) is a common endocrine disease. Prevalence is highest among postmenopausal women, with 1: 500 possibly being affected. Most patients are identified by an incidental finding of raised serum calcium during investigations for another condition. .

Pathological features 1/ 85% have a single parathyroid adenoma. Most of these tumors are small, less than 1 g (normal glands are 30 -50 mg). 2/ 10 -15% have multigland hyperplasia either as a sporadic disease or in association with familial disease (e. g. MEN syndromes; 3/ Parathyroid cancer is rare, representing less than 1% of patients.

Classical symptoms are described as: 1/Moan psychological/psychiatric symptoms (lethargy, depressed mood); 2/groan” non-specific gastrointestinal symptoms (abdominal pain, constipation); 3/bones” aches/pains localized in large joints; 4/Stones calcium based renal stones. 5/Polyuria, polydipsia, and nocturia are also common features. More than half of patients report no specific symptoms and accept most of the symptoms as part of generally getting older

Hypercalcaemic crisis can occur in patients with PHPT exposed to severe dehydration (e. g. diarrhoea/vomiting). In severe cases patients can present in coma

Diagnosis and investigations serum calcium is highly suggestive if unexplained but not diagnostic. serum parathyroid hormone concentration (PTH) in the presence of hypercalcaemia confirms the diagnosis (e. g. bone metastases (breast, renal, thyroid carcinoma) have a low PTH concentration). High-resolution neck ultrasound may identify tumors. Sestamibi (radioisotope) scanning used to localize adenomas (accurate in 50%)

Treatment Surgical treatment Bilateral neck exploration, visualization of all four parathyroid glands with excision of the enlarged one (s), has for many years been the standard treatment. It remains the treatment for those with negative localization scans.

Medical treatment Hypercalcaemic crisis needs aggressive rehydration. Establish large calibre IV access. Give 1 L in first hour, further 4 -6 L in first 24 h. Monitor urine output and central venous pressure until normalized.

Frusemide can be added to increase urinary excretion of calcium once rehydration is adequate. Bisphonates (e. g. IV pamidronate) should be avoided in PHPT when parathyroidectomy is anticipated, since they impair the ability to maintain normocalcaemia after the excision of an overactive parathyroid adenoma.

Secondary hyperparathyroidism (SHPT) refers to the excessive secretion of parathyroid hormone (PTH) by the parathyroid glands in response to hypocalcemia and associated hyperplasia of the glands. This disorder is especially seen in patients with chronic kidney failure

Multiple endocrine neoplasia Familial endocrine diseases constitute a group of rare conditions. Familial syndromes are autosomal dominant diseases involving tumors of several endocrine glands in a synchronous or metachronous pattern. Clinico pathological features Multiple endocrine neoplasia type I (MEN-1).

1/Parathyroid gland tumors. By age 40, 95% of patients have hypercalcaemia which is the commonest manifestation.

2/Pancreatic islet cell tumours. Prevalence of 30 -75%. Usually multicentric, slow-growing. Secrete multiple polypeptides (insulin and gastrin commonest). Gastrinoma leads to Zollinger-Ellison syndrome (recurrent and multiple peptic ulcers, severe reflux oesophagitis, and diarrhoea). Rarer tumours are VIPoma, glucagonoma, somatostatinoma

3/Anterior pituitary tumors. Detected in 15 -40%. Commonest is prolactinoma. Rarer are GH- (causes acromegaly) or ACTH(causes Cushing's disease) secreting tumours. 4/Carcinoid tumours (thymus, lungs, foregut), adrenal tumours, lipomas, and pinealomas have also been reported to appear in MEN-1 patients. MEN-1 gene encodes a nuclear protein menin (role unclear).

Multiple endocrine neoplasia type II (MEN-2) has two forms. 1/MEN-2 A is a syndrome with the following features. A/Medullary thyroid carcinoma (MTC): originates in the calcitonin-secreting parafollicullar C-cells commonly multicentric and bilateral and appear on a background of C-cell hyperplasia; presents as unilateral or bilateral thyroid nodules without associated cervical lymphadenopathy; associated secretion of other peptides can lead to severe diarrhoea. B/Phaeochromocytoma (in 50% of pt). C/Primary hyperparathyroidism (15% of

MEN-2 B is a syndrome with the following features. A/Medullary thyroid carcinoma (MTC). B/Phaeochromocytoma. C/Marfanoid specific body habitus (tall, slender, high arched palate, and long extremities) MEN-2 B is associated with mucosal neuromas and intestinal ganglioneuromatosis and characteristic facial appearance.