Pheochromocytomas are tumors of chromaffin cells of adrenal medulla or sympathetic ganglia. Chromaffin cells are derived from primary stem cells (sympathogonia) of embryonic neural crest tissue. Sympathogonia can differentiate into either neuroblasts and ganglion cells or pheochromoblasts and pheochromocytes. Tumors arising from these cells have related biochemical and histologic features and can produce similar clinical manifestations. Neuroblastomas and ganglioneuromas, arising from ganglion cells; and chemodectomas, arising from chemoreceptor cells, are related tumors. Pheochromocytoma also occurs in association with familial neurocutaneous disorders and with thyroid medullary carcinoma and hyperparathyroidism.
Like autonomic ganglia and the adrenal medulla, pheochromocytomas contain enzymes needed to metabolize dietary tyrosine to catecholamines. After uptake, tyrosine is hydroxylated to dihydroxyphenylalanine (DOPA) by the rate-limiting tyrosine hydroxylase step. Dihydroxyphenylalanine is decarboxylated to dihydroxyphenethylamine (dopamine) which in turn is oxidized to norepinephrine in the chromaffin granules. In tissues containing phenethanolamine- N - methyl