The detection of fungal elements and their characterization in patient specimens provides fundamental information. On histological sections fungi are most frequently seen on skin or mucosal surfaces or as mycotic thrombi or emboli that can occlude both arteries and veins in surgical specimen from immunocompromised patients or tissues obtained from autopsies. Microbial culture continues to be the central method for diagnosing fungal infection but is complemented by histomorphology using specific stains capable of identifying previously unsuspected fungal infections or for evaluating tissue invasion. These stains employ oxidizing reagents to create aldehyde binding sites on polysaccharides (1,2-glycol groups) of fungal cell walls for either Schiff's reagent or Silver ions. Gomori methenamine silver (GMS) and Periodic acid-Schiff (PAS) or their modifications are the most commonly used for tissue sections and in cytology specimens.
Keywords: Histochemistry; PAS stain; Schiffs’ reaction; Silver stain.