They are usually derived from the adrenal medulla but may develop from chromaffin cells in or about sympathetic ganglia (pheochromocytomas or paragangliomas).
The mechanism of catecholamine release is not well documented. It is suspected that the tumor may be caused by the changes in blood flow and necrosis within the tumor. The tumors do not contain nerves and therefore neural stimulation will not trigger catecholamine release. They also store and secrete a variety of peptides, such as endogenous opioids, neuropeptide Y, and chromagranin, which may contribute to the clinical manifestation in selected cases.
The term pheochromocytoma was coined by a pathologist named Pick after the Greek work phaios, meaning dark or dusky, and chroma, meaning color - to describe the chromaffin reaction seen in adrenomedullary tumors. The term is mostly used to refer to tumors that arise from the adrenal medulla.
Pheochromocytoma's most common manifestation is hypertension. Spectacular and alarming hypertensive paroxysms or crises may occur in over half the cases. Although they only occur in .1% of the hypertensive population, it is nevertheless a significant cause of high blood pressure and is correctible, if properly diagnosed and treated. If it is ignored, then it could be fatal and will put patients at risk for a lethal hypertensive paroxysm and long-term sequelae (a pathological condition resulting from a prior disease, injury or attack) of the disease. It is also an indication of the presence of a familiar disorder. An early detection may reduce the risk of metastasis.
Pheochromocytoma is a rare disease in which tumors form in chromaffin cells of the body. Most pheochromocytomas, about 98% of the time, start inside the adrenal glands (adrenal medulla). It is a tumor which is made up of large, polyhedral, pleomorphic chromaffin cells, which is only malignant in less than 10% of the case, and which causes the adrenal glands to produce too much adrenaline. The histologic appearance will not show malignancy. A local invasion of the surrounding tissue or distant metastases will reveal malignancy. It usually affects only one of the adrenal glands, although it may also start in other parts of the body, such as the area around the heart or bladder.
Statistically, pheochromocytoma occur in 1-2 out of 100,000 adults, around 80% of which are unilateral and solitary, only 10% are bilateral, and the remaining 10% are extraadrenal. Majority of these cases, about 80-90% are sporadic, and the remaining are connected to hereditary syndromes (.eg. multiple endocrine neoplasia). In pediatric patients, about are bilateral and another are extraadrenal. For yet unexplained reason, lesions are usually in the right side. Most pheochromocytomas are small, weighing less than 100 grams and are about 10 cm in diameter. They may however grow to over 3 kg in size. The tumors have vessels or ducts, or are highly vascular.
Extraadrenal pheochromocytomas usually weigh 20-40 g and are less than 5 cm in diameter. Most are located within the abdomen in association with the celiac, superior mesenteric ganglia. Approximately 1% are in the thorax, 1 percent are within the urinary bladder, and less than 1% are in the neck, usually in association with the sympathetic ganglia or the extracranial branches of the ninth or tenth cranial nerves.
Most of pheochromocytomas