FNA of Striated Duct Adenoma: Cytologic, Histologic, and Molecular Features of a Rare Salivary Gland Neoplasm.

Abstract

Striated duct adenoma (SDA) is a rare benign salivary gland neoplasm with limited cytologic characterization. We report a case of SDA with cytologic, histologic, immunohistochemical, and molecular correlation to further define its morphologic spectrum and diagnostic considerations. The patient was a 62-year-old male with a submandibular gland mass. Cytologically, the specimen demonstrated loose clusters of monomorphic epithelial cells ranging from cuboidal to rare elongated or slightly spindled morphology, with moderate amounts of variable oncocytic cytoplasm. Nuclei were ovoid and normochromatic with occasional nuclear grooves and infrequent pseudoinclusions. No significant nuclear atypia, mitotic activity, necrosis, or stromal components were identified. Using the 2nd Edition Milan System Classification, the case was categorized as Neoplasm: Benign (Category IVA). Histologic examination confirmed SDA, and next-generation sequencing identified an IDH2 p.R172M mutation. The cytologic and histologic features of SDA overlap with other salivary gland neoplasms, especially those with oncocytic/oncocytoid features. Definitive classification relies on histopathologic correlation and, when available, supportive molecular evidence of an IDH2 mutation.