Ectopic Olfactory Neuroblastoma of the Maxillary Sinus: A Case Report.

Olfactory neuroblastoma is a rare neuroendocrine tumor typically arising from the superior nasal cavity, and primary occurrence in the maxillary sinus is exceptionally uncommon, often leading to diagnostic confusion with other sinonasal malignancies. A 34-year-old man presented with bilateral nasal obstruction, recurrent epistaxis, and frontal headache, and imaging revealed a right maxillary sinus mass. Initial endoscopic biopsy suggested a differentiated neuroendocrine tumor, but whole-body octreotide scintigraphy was negative. The patient underwent endoscopic endonasal medial maxillectomy with complete tumor resection. Final histopathology demonstrated small round blue cells in lobular architecture, strong chromogranin and synaptophysin positivity, absence of mitoses or necrosis, and a low Ki-67 index, confirming Hyams grade I olfactory neuroblastoma. Adjuvant intensity-modulated radiotherapy was administered. The postoperative course was uneventful, and at 12-month follow-up there was no evidence of recurrence or metastasis. This case highlights that ectopic maxillary sinus olfactory neuroblastoma can mimic neuroendocrine carcinoma on limited biopsy, emphasizing the importance of complete resection and thorough histopathological evaluation for accurate diagnosis and grading. Hyams grade I disease in atypical locations carries an excellent prognosis with combined endoscopic surgery and radiotherapy, underscoring the prognostic value of Hyams grading and the need for long-term surveillance.