The adrenal glands are two small organs, one located above each kidney. They are triangular in shape and about the size of a thumb. The adrenal glands are known as endocrine glands because they produce hormones. These hormones are involved in control of blood pressure, chemical levels in the blood, water use in the body, glucose usage, and the “fight or flight” reaction during times of stress. These adrenal-produced hormones include cortisol, aldosterone, the adrenaline hormones – epinephrine and norepinephrine – and a small fraction of the body’s sex hormones (estrogen and androgens).

Adrenal incidentalomas fall into one of three categories:

• Functioning tumors – these tumors make too much of any of the hormones that the adrenal glands normally make and include aldosterone-producing adenomas (See Primary Hyperaldosteronism), cortisol-producing tumors (Cushing's Syndrome), adrenaline producing tumors ( Pheochromocytoma), or sex-hormone producing tumors.
• Malignant tumors – These tumors include adrenocortical cancer and metastatic disease.
• Benign, non-functional tumors – These tumors include adenomas, myelolipomas, ganglioneuromas, adrenal cysts, and hematomas.