Parotid Keratocystoma: Fine Needle Aspiration Cytomorphology With Ancillary Testing Results

Keratocystoma is a rare benign salivary gland tumor described in 1999. Only 14 cases have been reported in the histopathological literature, with three of them having had a preoperative fine needle aspiration (FNA) performed. All cytological diagnoses were not specific. We have seen a 12-month-old boy presenting a left parotid mass with facial nerve paralysis. FNA showed the presence of numerous mature squamous cells and some calcifications. The corresponding core needle biopsy showed identical morphologic features with no signs of malignancy. MAML2 FISH was negative, but IRF2BP2/RUNX2 fusion transcript was detected, which confirmed the diagnosis of keratocystoma. Despite its benign nature, keratocystoma should be differentiated from other salivary gland tumors such as Warthin's tumor with squamous cell metaplasia, mucoepidermoid carcinoma, primary vs. metastatic squamous cell carcinoma, and necrotizing sialometaplasia.