A 45-year-old woman presented with a polypoid nasal mass. The exact location in the nasal cavity was not specified. The patient underwent a biopsy and the resultant specimen is illustrated below.
Beneath attenuated but intact surface mucosa are irregular but sharply demarcated nests of epithelioid cells with enlarged, uniform nuclei and clearly visible nucleoli. There is no evidence of glandular or squamous differentiation. There is no necrosis. Mitotic figures are easily found but are not abundant.
What is your diagnosis?
Immunohistochemical studies were performed. The tumor was negative for epithelial markers. Results of immunohistochemical studies for S100 protein, calretinin and synaptophysin are shown below (in that order).
The cells surrounding the tumor nests are strongly positive for S100 protein, but the epithelioid cells within the nests themselves are negative. In contrast, the neoplastic epithelioid cells are strongly positive for calretinin, synaptophysin and chromogranin (not shown).
This is a nice example of an olfactory neuroblastoma (ONB).
These tumors virtually always arise from the superior nasal cavity, presumably from olfactory type cells or olfactory "inclined" stem cells in this region. Often they appear
as a vascular, polypoid mass. Involvement of the cribriform plate and direct extension in to the cranial cavity through the plate is common.
ONBs show considerable variation in their microscopic appearance, including the presence of Homer Wright type rosettes, and divergent glandular differentiation. The current example is at the "low grade" end of the spectrum, although we have not found grading these tumors to be of clinical value, as long as sinonasal undifferentiated carcinomas (SNUCs) are clearly separated from lesions considered to be high-grade ONBs.
ONBs typically show little or no cytokeratin positivity and strong positivity should lead to other diagnostic considerations. When the tumors form nice cell nests, as in this case, the presence of S100 positive sustentacular cells around the periphery of the nests is diagnostically helpful. Similar cells may be seen surrounding other neural or neuroendocrine-type lesions including paragangliomas and neuroblastomas. The prominent thick-walled capillaries seen in the second H&E image above are also characteristic of this tumor.
Prognosis for ONB is good if the lesions can be completely excised. Long-term followup is required, however, as recurrences and metastases have been documented after decade-long disease free intervals.