What is the fixative used for pheochromocytomas?

• A. Orth solution
• B. Zenker solution
• C. Absolute alcohol
• D. Formaldehyde

Answer: (A)

Pheochromocytoma tissue is rich in chromaffin granules that contain catecholamines. To visualize these granules histochemically, the fixative must preserve both the granules and the soluble catecholamines so that the chromaffin (chromate) reaction can occur and leave a distinctive brown deposit in the cells. Orth’s solution does exactly this: it includes potassium dichromate, which helps preserve catecholamines and chromaffin granules so the chromaffin reaction can be demonstrated after fixation. This makes it the preferred fixative for studying pheochromocytomas.

Absolute alcohol tends to dehydrate and extract soluble catecholamines, compromising the chromaffin content. Formaldehyde fixes tissue well but does not optimally preserve the chromaffin granules for chromaffin reaction visualization. Zenker’s solution is a strong fixative but involves heavy metals and may not provide the same reliability for chromaffin preservation as Orth’s solution. Therefore, Orth’s solution is the best choice for this purpose.