Olfactory Neuroblastoma with Divergent Differentiation: An Unusual Histologic Finding in a Rare Tumor.

Olfactory neuroblastoma (ONB) is a rare malignant neoplasm of the sinonasal tract that arises from olfactory epithelium. There have been reports, mainly in tumors treated with chemoradiation or with distant metastases, describing focal histologic changes of divergent cell populations within archetypal ONB. Only three cases have been reported of ONB coexisting with non-neuroendocrine tumors. We describe our experience with a 35-year-old male with a nasal cavity mass extending into the anterior cranial fossa. Pathology revealed this to be a high grade malignant neoplasm with features of olfactory neuroblastoma and a significant divergent population of pancytokeratin and epithelial membrane antigen-reactive cells. The patient underwent combined endoscopic and open craniofacial resection followed by adjuvant chemoradiation. We describe the clinical presentation, treatment, and outcome followed by a review of the literature. Surgical pathology clearly demonstrated two cell populations evenly distributed and displaying classic histologic and immunohistochemical markers of ONB, as well as poorly differentiated cells with an epithelial immunophenotype. The patient is now 16 months status post completion of treatment with no evidence of recurrence. Our patient's presentation is unique and unusual in that the tumor demonstrated a high grade olfactory neuroblastoma and a divergent, epithelial-marker reactive cell population in the same tumor. This combined appearance is unusual and may represent an "olfactory carcinoma". Only one previous case has reported carcinomatous involvement of an ONB. There is insufficient information in the literature to draw conclusions on the impact these divergent cell populations have on prognosis or treatment.