Fine needle aspiration cytology as an additional tool in the diagnosis of odontogenic keratocyst The aim of this study was to assess the use of fine needle aspiration cytology (FNAC) in diagnosis of odontogenic keratocyst (OKC), as well as to describe the cytological and immunohistochemical features. Eight consecutive patients submitted to FNAC and diagnosed with OKC were included in this study. FNAC was performed using 24-gauge needles attached to a 10-ml syringe, supported by a mechanical-syringe holder to facilitate aspiration. All cases provided a liquid or viscous content for smears that were either air-dried for Diff-Quick((R)) staining or immediately fixed in 95% alcohol and stained by the Papanicolaou technique. Incisional biopsies were carried out to confirm the diagnosis. Immunohistochemical reactions against anti-pan-cytokeratin (CK), CK14 and CK19 were performed in 3 mu m sections obtained from cell blocks and biopsy specimens. Cytologically many isolated or groups of keratinocytes with normal or ill defined nuclei were seen, besides numerous anucleated squamous cells and keratinous debris. Immunohistochemically, the keratin lamellae were positive for pan-cytokeratin and CK19, but negative for CK14. In biopsy specimens, CK14 expression was restricted to basal cells, while only the superficial cells were positive for CK19. In summary, FNAC is useful, reliable and safe tool for the preoperative diagnosis of OKC.186361366