MassonTrichrom

Masson trichrome is a histological staining method used to differentiate connective tissue from muscle, cytoplasm, and red blood cells in tissue sections. It is widely used in pathology and research to assess fibrosis and the relative amounts of collagen within tissues.

In the classic protocol, three pigments are used: a hematoxylin for nuclei, an acid dye for cytoplasm and muscle, and an aniline dye for collagen. The resulting colors typically show nuclei as dark blue or black, muscle and cytoplasm in red shades, and collagen fibers in blue. Some variations replace the blue collagen stain with a green tint (using different dyes such as light green or fast green), producing a green collagen appearance while maintaining red muscle and pink cytoplasm.

Procedure overview and variants: Masson trichrome staining is performed on formalin-fixed, paraffin-embedded sections. A common sequence is nuclear staining with hematoxylin, cytoplasmic/muscle staining with an acid dye (e.g., fuchsin or ponceau), and collagen staining with aniline blue, often followed by a differentiating step to sharpen color boundaries. Numerous variants exist that alter the order of dyes or substitute alternative stains for collagen.

Applications: The method is used to evaluate fibrotic changes, quantify connective tissue, and distinguish stroma from parenchyma in organs such as liver, kidney, and muscle. It is also employed in tumor pathology to assess the composition of the tumor microenvironment and to grade fibrosis.

Limitations: The technique is not specific for collagen type and staining intensity can vary with fixation, tissue processing, and technique. Consistent interpretation requires standardized protocols and proper controls.