All That Glitters Isn't Gold: Revisiting Fibrillary/Chondromyxoid Matrix in Salivary Gland Neoplasms - Insights from a Case Series with Histologic Correlation

Summary: Introduction: The reliability of fibrillary/chondromyxoid matrix in diagnosing salivary gland neoplasms via fine needle aspiration (FNA) remains a subject of debate. While its presence often suggests pleomorphic adenoma (PA), caution is warranted as other neoplasm may manifest similar features. Making diagnosis solely based on matrix features may lead to misclassification. This study scrutinizes the limitations of fibrillary matrix in cytological assessment, emphasizing the need for comprehensive evaluation to avoid diagnostic pitfalls. Materials and Methods: A natural language search was performed for salivary gland cytology cases between 2014-2024 revealed 645 cases. Then the search was limited by using ""matrix"" as a keyword in the comment section. 15 cases were found and 11 of these had concurrent surgical resections. 1 case diagnosed as multifocal PA in the surgical excision was excluded. FNA specimens of the remaining 10 cases were retrieved, and slides were reviewed. All cases showed variable amount of fibrillary/chondromyxoid matrix and were included in this study. Results: All cases had variable amount of fibrillary/chondromyxoid matrix and basaloid cells in the FNA slides, which brought pleomorphic adenoma as the primary differential for all of them. 5 cases were diagnosed after implementation of the Milan System (2017): 3 of them were called ""salivary gland neoplasm of uncertain malignant potential"" (SUMP), 1 case was called ""benign neoplasm"" (favor PA), and 1 case was called ""malignant"". Remaining 5 cases (before 2017) had descriptive diagnoses. Histologic correlations showed adenoid cystic carcinoma (1), poorly differentiated squamous cell carcinoma (2), myoepithelioma (2), epithelial-myoepithelial carcinoma (2) and basal cell adenoma (3) (See the Table and Figure). Conclusions: The cytologic evaluation of salivary gland neoplasms, particularly in cases involving fibrillary matrix, demands cautious interpretation. Recognizing differences in matrix quality and quantity; the pattern of neoplastic cells' distribution within the matrix material may be helpful in the differential diagnosis and is essential for improved patient management.