Pheochromocytomas are a type of tumor of the adrenal glands that can release high levels of epinephrine and norepinephrine. As the name implies, the adrenalglands are located near the "renal" (kidney) area. One adrenal gland sits on top of each of the two kidneys.
Despite their small size, the adrenal glands have many functions. They are complex endocrine (hormone secreting) glands. Cells in different regions of the adrenal glands have different functions in the endocrine system.The outer portion of the adrenal gland is called the adrenal cortex. In part of the adrenal cortex (zona fasciculata and zona reticularis) the cells secrete cortisol, a hormone similar to cortisone, which is essential for handling stresses In another area (zona glomerulosa) cells secrete a hormone called aldosterone which helps in water and salt regulation and blood pressure control.
The inner area of the adrenal gland is referred to as the adrenal medulla. This is where the cells secrete substances called catecholamines -- epinephrine, norepinephrine and dopamine. These are "flight or fight" hormones. They are responsible in part for that feeling of an "adrenaline" rush people feel when they are afraid. It is these cells that are overproduced by a pheochromocytoma. Basically, a pheochromocytoma is a tumor of these catecholamine-secreting cells, and that causes the clinical signs and symptoms we will discuss below. The catecholamine-secreting cells are sometimes referred to as chromaffin cells, and they are found in other areas of the body as well as in the adrenal medulla.
Sometimes, pheochromocytomas arise from chromaffin cells that are located outside of the adrenal gland. In this case, they are termed extra-adrenal pheochromocytomas or paragangliomas and are usually located in the abdomen.
Pheochromocytomas may occur in persons of any age. The peak incidence is between the third and the fifth decades of life. Pheochromocytomas are, fortunately, quite rare, and most of them are benign.