Ectopic primary olfactory neuroblastoma of the maxillary sinus.

Olfactory neuroblastoma (ONB) is a rare malignant tumor. Although the vast majority of cases arise in the nasal cavity, ONB is rarely reported in ectopic locations. We report a case of ONB in the maxillary sinus. A 63-year-old woman presented with left-sided nasal obstruction and epistaxis. Magnetic resonance imaging showed a nonenhancing left maxillary sinus tumor. Histologic sections showed ONB, Hyams grade IV, invading bone, skeletal muscle, and adjacent fibroadipose tissue. It is essential to be accurate when diagnosing sinonasal tumors because the differential diagnosis is broad, and one must consider the possibility of ectopic ONB, although it is rare. The behavior of ONB and other neuroendocrine tumors of the sinonasal region is quite different, and there are varied approaches to treatment. Therefore, an accurate diagnosis as well as correct grade and stage must be assigned.