Sclerosing Polycystic Adenoma Masquerading as Malignancy on Fine Needle Aspiration Cytology

Sclerosing polycystic adenoma (SPA) is a rare benign salivary gland neoplasm composed of a lobular proliferation of ducts lined by cuboidal, columnar, apocrine, and foamy vacuolated cells, and acinar structures having large cells with intracytoplasmic bright eosinophilic granules in a collagenous stroma with lymphoid aggregates. Due to its rarity, its cytological features are not widely documented. The spectrum of cell types may lead to it being mistaken for malignancy on cytological examination. This 29-year-old male presented with a right parotid swelling measuring 4 cm on ultrasonography. Fine needle aspirate showed tightly cohesive three-dimensional papillaroid and acinar clusters along with flat sheets of large polygonal cells with abundant coarse granular to vacuolated cytoplasm in a dirty fluidy background. Oncocytoid and apocrine-appearing cells were present. The background showed few lymphocytes and stromal fragments. A diagnosis of a malignant neoplasm, possibly oncocytic mucoepidermoid carcinoma, was given. Total conservative parotidectomy with selective neck dissection was performed. The resection specimen revealed features of SPA with loss of PTEN immunostaining in the ductal and acinar cells. SPA may mimic carcinomas like mucoepidermoid, salivary duct and acinic cell carcinoma on cytology, and may also be associated with an in situ or invasive carcinoma. The diagnosis of SPA was not made on cytology in any of the eight prior cytology reports, and the possibility of malignancy was considered in three. Accurate cytologic diagnosis of SPA can obviate the need for neck dissection.