Poorly differentiated sinonasal neuroendocrine carcinoma with skull base invasion: A case report.

Background: Sinonasal neuroendocrine carcinoma is a rare head and neck tumor that represents only 5% of sinonasal neoplasms. This lesion has a high risk of invasion to adjacent structures such as the orbit, skull base, and soft tissues, with symptoms usually being nonspecific. Most cases are diagnosed in late stages, decreasing overall survival without treatment. To date, there is no consensus on management given its low prevalence; however, it has been shown that multimodal therapy, with the correct surgical approach as the mainstay, offers a better disease-free prognosis. Case Description: A 46-year-old woman presented with a 1 year history of nasal symptoms, characterized by obstruction and epistaxis. Imaging studies showed an extra-axial mass causing skull base erosion and displacement of the right fronto-orbital region, without invasion of brain parenchyma or meninges. A biopsy was performed and an unresectable poorly differentiated sinonasal neuroendocrine carcinoma was diagnosed. Treatment with radio and chemotherapy was initiated and, as the tumoral volume decreased, she was referred for neurosurgical intervention; an endonasal endoscopic approach was performed. Gross total resection was achieved and the patient was discharged without postoperative complications and no residual lesion on imaging. Conclusion: We describe the evolution of a rare advanced-stage neoplasm. It highlights that despite receiving an initial diagnosis of an unresectable mass, multimodal therapy, and an adequate surgical approach deemed the entire lesion to be resected. Despite the favorable clinical evolution, the follow-up of neuroendocrine carcinoma is prioritized as a neoplasm with a high rate of recurrence and metastasis.