Anatomical and Oral Pathology Including Workshops
The spectrum of ‘small round blue cell’ neoplasms is broad, but within the sinonasal tract (SNT), tumours of the dispersed neuroendocrine cell system narrow to olfactory neuroblastoma (ONB), pituitary adenoma, melanoma, and neuroendocrine carcinoma. A single totipotential cells shows multidirectional differentiation along epithelial and neuroendocrine lines. ONB arise from the neuroepithelial olfactory cells involving the cribriform plate of the ethmoid. With a bimodal age distribution (2nd and 6th decades), symptoms are non‐specific, frequently delaying diagnosis. Histologically, a lobular architecture is maintained irrespective of the tumour grade. Circumscribed lobules are outlined by S100 protein positive supporting cells, while the neoplastic cells are arranged in a syncytial architecture with a background of neuronal processes. Pseudorosettes (Homer Wright) are more common than true rosettes (Flexner‐Wintersteiner). The cells are small to medium sized, set in a richly vascularised fibrovascular stroma. The nuclei are round with delicate, ‘salt‐and‐pepper’ chromatin distribution with small nucleoli. Pleomorphism, mitoses, and necrosis increase with tumour grade. The cells show neuroendocrine immunoreactivity (chromogranin, synaptophysin, NSE, CD56), with rare keratin positive cells. Grade and stage affect prognosis. There is no EWS/FLI‐1 gene fusion. Many tumours in the SNT mimic ONB and must be excluded due to differences in treatment and prognosis.