Pheochromocytoma : Chromaffin Reaction

The gross appearance of pheochromocytoma ranges from pink-tan to yellow to slightly brown. The freshly cut tumor surface turns dark brown (right half of image) when immersed in potassium dichromate solution (pH between 5 and 6). This is due to oxidation of stored catecholamines synthesized by the tumor and is known as the Chromaffin Reaction. Pheochromocytomas have the capacity to synthesize both norepinephrine and epinephrine, where as extra-adrenal paragangliomas can synthesize only norepinephrine (as they lack the enzyme phenylethanolamine-N-methyl transferase required for methylation of norepinephrine to epinephrine). Image courtesy of Dr. Jean-Christophe Fournet, Paris, France; humpath.com; Used with permission