What is the fixative for Masson Trichrome?

• A. Bouin
• B. 10% NBF
• C. Osmium tetroxide
• D. Zenkers

Answer: (A)

Masson Trichrome needs a fixative that preserves tissue in a way that collagen can be highlighted distinctly from muscle and cytoplasm. Bouin's solution, a picric acid–formalin–acetic acid fixative, does just that. It helps the tissue take up the blue dye for collagen more reliably, so collagen appears blue while muscle and cytoplasm stain red or pink, giving the clear contrast the stain is designed for. Other fixatives don’t produce this differential pattern: 10% neutral buffered formalin is a general fixative that doesn’t optimize the collagen staining; Osmium tetroxide is used for lipids and electron microscopy and would alter staining in unintended ways; Zenkers fixative isn’t the standard choice for this protocol and wouldn’t yield the classic Masson Trichrome colors. Keep in mind Bouin's is hazardous due to picric acid and requires proper handling and thorough washing after fixation.