Olfactory neuroblastoma: A clinicopathological experience of a rare entity from Pakistan

Objectives: To present the clinicopathological experience of Olfactory Neuroblastoma (ONB) with emphasis on histopathological and immunohistochemical features. Methods: A descriptive cross-sectional study was done on 36 cases of ONB, selected by non-probability purposive sampling. Theses cases of ONB were retrieved and reviewed from surgical pathology database of Aga Khan University Hospital reported between January 1993 and March 2015. Results: Tumor size and age of presentation was wide in range without any distinct bimodal distribution. Nasal cavity was most common site along with involvement of paranasal sinuses. More than 50% cases had Kadish stage A. Microscopically, most cases were Grade-1 and majority showed partial or complete lobular architecture. Neurofibrillary matrix was observed in 2/3^rd of cases. Among immunohistochemical markers, Neuron Specific Enolase was most frequently expressed. Unusual positive expression of Cytokeratin AE1/ AE3 and Cytokeratin CAM5.2 was also seen focally in few cases. Conclusion: The ONB has great variability of histological and clinical presentation, and immunohistochemical markers are useful to differentiate from more common small round blue cell tumours of nasal cavity.