Parathyroid gland adenoma. Light micrograph of a section through an adenoma, a benign (non-cancerous) tumour, in the parathyroid gland. The adenoma cells, also called oxyphils, have large and irregular nuclei (purple dots). There are two pairs of parathyroid glands situated behind the thyroid gland in the neck, which control the blood's calcium and phosphorus levels. The adenoma may result in hyperparathyroidism, which causes an excess of calcium (hypercalcaemia) and a shortage of phosphorus in the blood. Treatment is by surgical removal of the gland, followed by blood regulating drugs that maintain normal calcium and phosphorus concentrations.