Acinic cell carcinoma-papillary cystic variant. Pitfalls of fine needle aspiration diagnosis: study of five cases and review of literature

Acinic cell carcinoma (ACC) accounts for 12-17% of primary salivary gland carcinomas and 3.4% of all salivary gland neoplasms. ACC-papillary cystic variant (PCV) is a distinct subtype with clear-cut and well-defined morphological features as revealed in tissue sections, but it is more difficult to diagnose accurately on fine needle aspiration (FNA). The aim of this article was to discuss the causes of the erroneous interpretation as well as to draw attention of practicing pathologists to this rare and unique variant of ACC. A computerized search of surgical and cytopathology files identified five diagnoses of ACC-PCV that were preceded by an FNA performed in-house with available slides for review. Cytological features were compared to histomorphological features of excisional surgical pathology specimens. Cytomorphological findings from these ACC-PCV cases have varied features that can be broadly divided in two major subtypes: hypocellular cystic specimens containing histiocyte-like vacuolated cells (two cases) and more cellular specimens containing papillary clusters of cells with a polymorphous appearance including granular cells, vacuolated cells and nondescript small cuboidal cells (three cases). Hypocellular, cyst-like specimens pose a diagnostic problem when using FNA, as they can easily be misinterpreted as a benign cyst of the salivary gland. Our review of cases found certain 'red flags' that should prompt pathologists to further investigate the true acinic origin of hypocellular cystic specimens. On close morphological examination, these specimens revealed the presence of tight cellular clusters, distinct cytoplasmic borders, larger nuclei with distinct nucleoli and binucleated cells.