Pheochromocytoma refers to a generally benign (90%) but biologically active tumor arising from the chromafin cells of the adrenal medulla that secrete catecholamines. Extra-adrenal pheochromocytomas are called paragangliomas. It is the secretion of catecholamines that causes the majority of symptoms in these patients.
The tumor occurs at any age, is slightly more common in women, and, although most cases occur sporadically, a minority of cases are familial (approximately 10%). Familial cases may arise as part of the Multiple Endocrine Neoplasia types IIa and IIb. Although rare it must be considered in any case of refractory hypertension. The tumor is amenable to surgical resection. The importance of maintaining a high index of suspicion is emphasized by the fact that up to 50% of pheochromocytomas are found coincidentally at autopsy.
The clinical features include: weight loss; refractory hypertension; episodic hypertension with or without associated symptoms such as headache, diaphoresis, palpitations, tachycardia, abdominal pain; end organ damage from uncontrolled hypertension; malignant hypertension; or hypertensive crisis. Lab abnormalities seen with pheochromocytoma include hyperglycemia and leukocytosis.
Paroxysmal hypertensive episodes or crises may occur during or after activities that place pressure on the abdominal contents. Other precipitants include: contrast media, tricyclic antidepressants, cocaine, childbirth, and opiates.
Increased total urinary catecholamines and catecholamine metabolites, specifically vanillylmandelic acid and metanephrine, are usually diagnostic. Ideally this 24-hour urine collection should be performed after a crisis.
CT scan and MRI are helpful in both the confirmation and localization of a pheochromocytoma. They each have a sensitivity of about 90%. Tumors vary from solid, to complex, and even predominantly cystic. Calcification can occasionally be seen. The mass shows strong contrast enhancement with CT scanning and high signal intensity on T2 weighted MR imaging.
If CT and MRI fail to localize the tumor, functional imaging with MIBG (iodine labeled metaiodobenzylguanidine) can be performed. MIBG structurally resembles norepinepherine and thus concentrates in neuroectodermal tissues making it ideal for adrenal imaging.
Most tumors are 5 to 6 cm in diameter and weigh 80 to 100g. The ‘rule of 10s’ is an approximation that 10% are bilateral, 10% are familial, 10% are extra-adrenal, and 10% are malignant. Unique pathological characteristics include immunohistochemical stains revealing the presence of the neuron specific chromogranin. There are no reliable histological criteria to distinguish benign from malignant tumors. If metastases occur (10%) the most common locations are regional lymph nods, bone, lung, and liver.
Definitive treatment is surgical removal while alpha and beta adrenergic blocking agents can be stabilizing peri- and intraoperatively.
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