Pheochromocytomas are not a common medical/surgical problem. They are estimated to cause only 0.1–0.5% of all cases of hypertension [1,2], and are seen in 4–7% of patients with incidentally found adrenal adenomas [2,3]. That being said, at some time in their careers medical consultants are likely to be asked to evaluate a patient with a suspected pheochromocytoma. Because catecholamines have major regulatory effects on many different body systems, it is vital that these be anticipated and properly managed in the perioperative period. Pheochromocytomas are associated with an increased risk of adverse reactions to many commonly prescribed drugs and clinicians must also be aware of this potential hazard. The removal of a pheochromocytoma has great potential for complications, both during and after surgery because of the release of catecholamines during manipulation or stimulation of the tumor. Pathophysiology Pheochromocytomas arise from chromaffin cells of the neural crest that migrate to form the adult adrenal medulla and sympathetic ganglia. These cells synthesize catecholamines through a series of enzymatically controlled steps, starting with the conversion of tyrosine to dihydroxyphenylalanine (dopa) by tyrosine hydroxylase. This is the rate-limiting step in catecholamine synthesis. Dopa is then converted to dopamine, which is subsequently decarboxylated to norepinephrine. The methylation of norepinephrine to epinephrine is accomplished through the action of phenylethanolamine-N-methyl transferase, an enzyme that is induced by glucocorticoids that reach the adrenal medulla in high concentrations through the corticomedullary venous sinuses from the adrenal cortex. Norepinephrine and epinephrine are the major products of most pheochromocytomas . Epinephrine is produced mainly in the adrenal medulla; thus, a pheochromocytoma that produces epinephrine is nearly always located in the adrenal gland. Norepinephrine is produced and secreted in the central nervous system and the sympathetic post-ganglionic nerve endings as well as in the adrenal medulla. Dopamine is also produced and secreted by some pheochromocytomas. The metabolism of catecholamines takes place mostly in the same cells where the catecholamines are synthesized . Once catecholamines reach the plasma, they have a half-life of only 1–2 minutes before they are taken up by cells or enzymatically degraded . Metanephrine, normetanephrine, and vanillylmandelic acid are the major metabolites.
|Original language||English (US)|
|Title of host publication||Medical Management of the Surgical Patient: A Textbook of Perioperative Medicine, Fifth Edition|
|Publisher||Cambridge University Press|
|Number of pages||4|
|ISBN (Print)||9780511920660, 9781107009165|
|State||Published - Jan 1 2010|
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