RESUMEN
<p><b>OBJECTIVE</b>To investigate unusual pathological features of olfactory neuroblastoma (ONB) and its correlation with the clinical prognosis.</p><p><b>METHODS</b>Totally 40 cases of ONB were studied using histology and immunohistochemistry techniques. All the cases of ONB were graded according to Hyams Grading system.</p><p><b>RESULTS</b>ONB consisted of small round tumor cells growing in nests or lobules separated by fibrovascular septa. Characteristically, there were neurofibrillary intercellular matrices and Homer-Wright or Flexner-Wintersteiner rosette formation. The unusual structures including epithelial components such as mucous or squamous cell nests which were found in 45.0% (18/40), and 15.0% (6/40) respectively. In addition, 3 cases showed an in-situ form with invasion of tumor into olfactory epithelium, and there was exogenous papillary proliferation seen in 2 cases. Log-rank survival analysis demonstrated that Hyams Grading had no statistical correlation with the prognosis. The presence of necrosis was correlated with a poor prognosis (P = 0.016) while the presence of mucous cells was correlated with a good prognosis (P = 0.011).</p><p><b>CONCLUSIONS</b>Unusual pathological structures including epithelial structures, in-situ invasion of tumor tissue into the involving olfactory epithelium and exogenous papillary proliferation can be found in ONB, suggesting that ONB may originate from the undifferentiated basal cells of olfactory epithelium, through bipotential differentiation. The presence of tumor necrosis in ONB is a poor prognostic indicator while the presence of mucous cells suggests a good prognosis.</p>