When the amount of cortisol in the blood is adequate, the hypothalamus and pituitary release less CRH and ACTH . This ensures that the amount of cortisol released by the adrenal glands is precisely balanced to meet the body's daily needs. However, if something goes wrong with the adrenals or their regulating switches in the pituitary gland or the hypothalamus , cortisol production can go awry. Pituitary Adenoma Pituitary adenomas cause most cases of Cushing's syndrome . They are benign , or non-cancerous, tumors of the pituitary gland which secrete increased amounts of ACTH .
Most patients have a single adenoma .
This condition is known as ectopic ACTH syndrome . Lung tumors cause over 50 percent of these cases. Men are affected 3 times more frequently than women. The most common forms of ACTH-producing tumors are oat cell, or small cell lung cancer, which accounts for about 25 percent of all lung cancer cases, and carcinoid tumors . Other less common types of tumors that can produce ACTH are thymomas , pancreatic islet cell tumors , and medullary carcinomas of the thyroid .