Pheochromocytoma is a rare tumor that develops in the adrenal glands. There are two adrenal glands in the human body, which are located on top of the kidneys. Each adrenal gland has two parts, the outer cortex and inner medulla. The cortex produces corticosteroid and androgen hormones. The medulla produces catecholamines (epinephrine, norepinephrine, and dopamine).
Pheochromocytomas may be found in one or both glands and may spread, or metastasize (pronounced meh-TAS-tuh-size), beyond the adrenal glands. Pheochromocytomas develop from the center of the adrenal gland, in an area called the adrenal medulla, which secretes catecholamines.1
Hormones that are normally produced by the adrenal medulla, catecholamines (pronounced kat-i-KOL-uh-meens), help to regulate heart rate, blood pressure, and the body's responses to stress. Pheochromocytomas release additional catecholamines, causing higher than normal amounts in the body.2 Changes in hormone levels produce some of the clinical signs and life-threatening symptoms of pheochromocytoma.
About 70% of pheochromocytomas are benign (non-cancerous or non-metastatic); 30% are malignant (cancerous or metastatic) and spread to other parts of the body.3 Common sites to which malignant pheochromocytomas spread, or metastasize, include the liver, lungs, bone, and distant lymph nodes.2
On this webpage, the term pheochromocytoma also refers to paraganglioma unless otherwise specified.
Paragangliomas are tumors originating from neuronal tissue; they were formerly called extra-adrenal pheochromocytomas. There are developmentally two subgroups of these tumors: parasympathetic paragangliomas and sympathetic paragangliomas. These subgroups differ in the type of tissue from which they form (parasympathetic versus sympathetic) and also in their location and hormonal production. Parasympathetic tissue is important for certain body processes, including salivation, urination, and digestion. Sympathetic tissue forms the tissue important for "fight-or-flight" responses.
The group of paragangliomas that develop from parasympathetic-associated tissue in the head and neck are usually referred to as "head and neck paragangliomas." These tumors can be locally invasive but usually do not metastasize or produce catecholamines (stress hormones). Signs and symptoms of head and neck paragangliomas are usually due to the tumor mass itself instead of the secreted catecholamines.
Paragangliomas that develop from sympathetic neuronal tissue are usually localized in the chest, abdomen, or pelvis. These tumors often have excessive hormone secretion, which makes them very similar to pheochromocytomas. As a result of excessive hormone secretion, paragangliomas often cause the signs and symptoms described below (e.g., heart palpitations, irregular heartbeat, hypertension, and sweating). Sympathetic (or extra-adrenal) paragangliomas generally tend to be more malignant than pheochromocytomas (localized to the adrenal gland).4
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