Parathyroid Adenoma

A parathyroid adenoma is a benign tumour of the parathyroid gland, typically causing hyperparathyroidism. Rarely, parathyroid adenomas are not associated with hyperparathyroidism. Humans generally have four parathyroid glands located on the posterior surface of the thyroid gland in the neck. These glands play a central role in calcium metabolism by secreting parathyroid hormone (PTH), which increases calcium levels in the blood by stimulating bone resorption and renal reabsorption of calcium.

The effects of PTH are counteracted by calcitonin. When a parathyroid adenoma leads to hyperparathyroidism, excessive PTH is secreted, resulting in elevated blood calcium levels, known as hypercalcaemia.

Overview

Signs and Symptoms

Initial signs of parathyroid adenoma and consequent primary hyperparathyroidism may include bone fractures and urinary calculi such as kidney stones. Often, the condition is incidentally diagnosed through blood tests showing high calcium levels, even in asymptomatic patients. Symptomatic patients may experience joint, muscle, and abdominal pain or discomfort; depression and mood changes due to hormonal imbalances; constipation; exhaustion; and kidney damage.

Genetics

Parathyroid adenomas can be linked to the overexpression of the cyclin D1 gene and are also associated with multiple endocrine neoplasia (MEN).

Diagnosis

Hyperparathyroidism is confirmed through blood tests measuring calcium and PTH levels. A specific diagnostic test for parathyroid adenoma is sestamibi parathyroid scintigraphy, also known as the sestamibi scan. This nuclear imaging technique identifies and locates pathological parathyroid tissue.

4DCT scanning is used as a secondary diagnostic tool. This technique provides three-dimensional imaging along with temporal changes of iodinated contrast enhancement, presenting the images in a video format from plain imaging to arterial to venous and delay phases. Parathyroid adenomas typically show low density on non-contrast images, peak enhancement during the arterial phase, and gradual fading until the delay phase.

Treatment

Surgery is the definitive cure for parathyroid adenomas, with a success rate of about 95%. The surgical procedure, known as parathyroidectomy, involves the removal of the affected gland(s). Initially, a bilateral neck exploration was the standard approach, where both sides of the neck were opened to identify and remove the affected tissue. By the 1980s, unilateral exploration became more common. Advances in imaging techniques have now enabled minimally invasive parathyroidectomy, including smaller open procedures, radio-guided and video-assisted procedures, and totally endoscopic surgery.

Pre-surgical localisation of the affected glandular tissue is essential. Although parathyroid glands are typically located on the back of the thyroid, their position can vary, with approximately 10% of parathyroid adenomas being ectopic and located elsewhere, such as in the mediastinum of the chest. This variability necessitates the use of various imaging techniques like sestamibi scans, single-photon emission computed tomography (SPECT), ultrasound, MRI, and CT scans. In some cases, parathyroid adenomas can be ablated using ethanol injection, laser, or radiofrequency guided by ultrasound.

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Self-assessment MCQs (single best answer)

What is a parathyroid adenoma?

What condition is typically caused by a parathyroid adenoma?

What role do parathyroid glands play in the body?

What is the primary symptom of hyperparathyroidism due to a parathyroid adenoma?

Which diagnostic test is specific for identifying parathyroid adenoma?

What is the definitive treatment for a parathyroid adenoma?

Which imaging technique is used as a secondary diagnostic tool for parathyroid adenoma?

Which gene is often overexpressed in parathyroid adenomas?

What percentage of parathyroid adenomas are ectopic?

Aside from surgery, what other treatment can be used for parathyroid adenomas?