Selective Utility of Periodic Acid-Schiff Staining in Sinonasal Masses: A Cross-Sectional Observational Study

Introduction Sinonasal masses encompass inflammatory, infective, benign neoplastic, and malignant lesions with overlapping clinical and microscopic features. Periodic acid-Schiff (PAS) staining can demonstrate carbohydrate-rich mucin, basement membrane material, and fungal cell walls, but its incremental value when applied routinely to all sinonasal specimens is uncertain. This study evaluated the component-specific and confirmatory utility of PAS staining in routine sinonasal histopathology. Methods This prospective, single-center, cross-sectional observational study included 162 consecutive eligible sinonasal biopsy and resection specimens received from March 2025 to December 2025. Routine hematoxylin and eosin (H&E) sections were examined before standard PAS staining. Demographic data, site, broad histological category, necrosis, morphologically localized PAS-reactive mucin, fungal elements, and the effect of PAS on interpretation were recorded. Fisher's exact test was used to assess the association between necrosis on H&E and fungal demonstration by PAS. Results Patients ranged from eight to 75 years of age, with a mean age of 31.5 years (standard deviation: 18.1). The nasal cavity was involved in 151 cases (93.2%). Non-neoplastic lesions accounted for 128 cases (79.0%), benign neoplasms for 22 (13.6%), and malignant neoplasms for 12 (7.4%); inflammatory nasal polyp was the most frequent individual diagnosis (110 cases). PAS-reactive mucin was identified in 119 cases (73.5%) but did not independently modify the final histopathological interpretation. Fungal elements were demonstrated by PAS in all 19 cases with prior H&E-based suspicion and in none of the 143 cases without preceding H&E suspicion. These findings reflect confirmatory agreement within the routine sequential diagnostic workflow and should be interpreted as evidence of the supportive role of PAS rather than its independent diagnostic performance. Among 31 cases with necrosis, 19 (61.3%) showed fungal elements, compared with none of the 131 cases without necrosis (Fisher's exact p<0.001). PAS did not substantially alter the broad histological category but provided confirmatory support in cases with morphologically suspected fungal infection. Conclusion Routine PAS staining of every sinonasal specimen had limited additional diagnostic contribution in this cohort. As PAS evaluation was performed after H&E review, its independent screening performance could not be assessed. Its main utility was targeted confirmation and enhanced visualization of fungal organisms in morphologically suspicious cases, particularly those with necrosis. PAS should therefore be used as a selective ancillary stain guided by routine histological findings rather than as a universal screening stain for all sinonasal specimens.