Another technique for demonstrating the tissue component stained black in the image is which of the following?

• A. PAS
• B. Masson's trichrome
• C. Verhoeff
• D. Alcian blue

Answer: (A)

The technique being tested highlights carbohydrate-rich structures. Periodic acid–Schiff (PAS) reacts with aldehyde groups formed from sugars in glycogen, mucopolysaccharides, and mucins, producing a magenta color that can appear very dark in many images. If the tissue component shown in the image is a carbohydrate-containing structure, PAS is the best choice because it specifically stains those substances, making them stand out against the rest of the tissue.

The other stains target different components: Masson's trichrome colors collagen blue and muscle/red, so it wouldn’t selectively highlight carbohydrate-rich structures in black. Verhoeff’s elastic stain highlights elastic fibers in dark colors but not carbohydrates. Alcian blue stains acidic mucopolysaccharides blue, not black. So PAS uniquely emphasizes the carbohydrate-containing elements that could appear as a very dark, nearly black color in the image.