Parathyroid adenoma overview

# Overview
A parathyroid adenoma is a benign tumor of the parathyroid gland. Parathyroid adenoma can be associated with overexpression of the cyclin D1 gene. An elevated concentration of
serum calcium and serum parathyroid hormone is diagnostic of parathyroid gland. A specific test for parathyroid adenoma is sestamibi parathyroid scintigraphy, the sestamibi scan. Surgery is the mainstay of treatment for parathyroid cancer.

# Pathophysiology
- A parathyroid adenoma is a benign tumor of the parathyroid gland. It generally causes hyperparathyroidism; there are very few reports of parathyroid adenomas that were not associated with hyperparathyroidism.
- A human being usually has four parathyroid glands located on the back surface of the thyroid in the neck. The parathyroids secrete parathyroid hormone (PTH), which increases the concentration of calcium in the blood by inducing the bones to release calcium into the blood and the kidneys to reabsorb it from the urine. When a parathyroid adenoma causes hyperparathyroidism, more parathyroid hormone is secreted, causing the calcium concentration of the blood to rise, resulting in hypercalcemia.

## Genetics
- Parathyroid adenoma can be associated with overexpression of the cyclin D1 gene.

## Gallery
- Adenoma 01.jpg
Intermediate/Low magnification micrograph of parathyroid adenoma. H&E stain. Features: Single cell population forming a single mass. Thin capsule. No adipose tissue. +/-Glandular architecture (which may lead to confusion with thyroid tissue). Normal parathyroid gland with prominent adipose tissue is seen on the right of the image.

# Risk Factors
- The following risk factors may increase a persons chance of developing a parathyroid adenoma:
- Multiple endocrine neoplasia type 1 (MEN 1)
- Familial isolated hyperparathyroidism(FIHP)
- Hyperparathyroidismjaw tumour (HPT-JT) syndrome
- Radiation therapy to the head or neck

# Diagnosis

## Diagnostic Criteria
Hyperparathyroidism is confirmed by blood tests such as calcium and parathormone levels.

## Symptoms
- Fatigue
- Confusion
- Nausea
- Constipation
- Kidney stones
- Muscle aches
- Bone fracture

## CT
- CT can be very useful for localising the lesion when the site is not known. Shows increased uptake with agents such as Technetium (Tc) 99m Sestamibi (MIBI) (commonly used agent) and Tc-99m tetrofosmin. The nuclear medicine scan can be fused with the CT scan as a SPECT scan increase diagnostic accuracy.
- In the past CT was more commonly used in the setting of a failed parathyroidectomy for the detection of suspected ectopic glands (often mediastinal).  However, in recent years, 4D-CT has emerged as valuable modality especially in the era of minimally invasive parathyroidectomy. This type of surgery requires precise localization with anatomical detail and a confident diagnosis of parathyroid adenoma. 4DCT has been shown to be more sensitive than sonography and scintigraphy for preoperative localisation of parathyroid adenomas.
- Enhancement on 4D-CT
- On 4D-CT parathyroid adenomas typically demonstrate intense enhancement on arterial phase, washout of contrast on delayed phase, and low attenuation on non-contrast imaging.
- Secondary signs include:
- The polar vessel which represents an enlarged feeding artery or draining vein to the hypervascular parathyroid adenoma
- A larger lesion size increases the confidence of diagnosis
- Parathyroid adenomas can also have cystic change

## MRI
- MRI is infrequently utilized in initial work up because of lower spatial resolution and artifacts. Adenomas can show variable signal intensity on MRI. Reported signal characteristics include:
- T1
- Typically intermediate to low signal
- Subacute haemorrhage can cause high signal intensiy
- Fibrosis or old haemorrhage can cause low signal intensity
- T2
- Typically hyperintense
- Subacute haemorrhage can cause high signal intensity
- Fibrosis or old haemorrhage can cause low signal intensity
- Since most lesions demonstrate high T2 signal intensity, the addition of contrast for MR scanning does not significantly increase detection.

## Ultrasound
- Ultrasound is one of most commonly used initial imaging modalities.
- Greyscale
- Most nodules need to be >1cm to be confidently seen on ultrasound
- Parathyroid adenomas tend to be homogeneously hypoechoic to the overlying thyroid gland
- An echogenic thyroid capsule separating the thyroid from the parathyroid may be seen
- Doppler ultrasound
- Can commonly show a characteristic extrathyroidal feeding vessel (typically a branch off the inferior thyroidal artery), which enters the parathyroid gland at one of the poles. Internal vascularity is also commonly seen in a peripheral distribution. This feeding artery tends to branch around the periphery of the gland before penetration. This feature can give a characteristic arc or rim of vascularity. The overlying thyroid gland may also show an area of asymmetric hypervascularity that may help to locate an underlying adenoma.

## Other Imaging Findings
- A specific test for parathyroid adenoma is sestamibi parathyroid scintigraphy, the sestamibi scan. This nuclear imaging technique reveals the presence and location of pathological parathyroid tissue.

## Gallery
- Sharply marginated, hypoechogenic lesion at the dorsal lower pole of the left thyroid lobe.
- High magnification micrograph of a parathyroid adenoma. H&E stain. Features: Single cell population forming a single mass. Thin capsule. No adipose tissue. +/-Glandular architecture (which may lead to confusion with thyroid tissue). Normal parathyroid gland with prominent adipose tissue is seen on the right of the image
- Parathyroid adenoma
- Parathyroid adenoma
- Parathyroid adenoma
- Parathyroid adenoma
- Parathyroid adenoma

# Treatment

## Surgery
- Surgery is the only cure for parathyroid adenomas. It is successful about 95% of the time. Parathyroidectomy is the removal of the affected gland(s). The standard of treatment of primary hyperparathyroidism was formerly a surgical technique called bilateral neck exploration, in which the neck was opened on both sides, the parathyroids were identified, and the affected tissue was removed. By the 1980s, unilateral exploration became more common. Parathyroidectomy can now be performed in a minimally invasive fashion, mainly because imaging techniques can pinpoint the location of the tissue. Minimally invasive techniques include smaller open procedures, radio-guided and video-assisted procedures, and totally endoscopic surgery.
- Before surgery is attempted, the affected glandular tissue must be located. Though the parathyroid glands are usually located on the back of the thyroid, their position is variable. Some people have one or more parathyroid glands elsewhere in the neck anatomy or in the chest. About 10% of parathyroid adenomas are ectopic, located not along the back of the thyroid but elsewhere in the body, sometimes in the mediastinum of the chest. This can make them difficult to locate, so various imaging techniques are used, such as the sestamibi scan, single-photon emission computed tomography (SPECT), ultrasound, MRI, and CT scans.