Primary Small Cell Carcinoma of Left Maxillary Sinus: A Case Report of Rare Tumor on Rare Location

Introduction: Primary extrapulmonary small cell carcinoma (EPSCC) is a rare and aggressive tumor with diverse clinical manifestations. In the realm of head and neck pathology, EPSCC most commonly presents in the larynx or oral cavity. Sinonasal small cell neuroendocrine carcinoma represents a particularly infrequent and aggressive neoplasm affecting the nasal cavity and paranasal sinuses. Case Presentation: Here in, we are presenting a case of a 40-year-old nonsmoking male with left maxillary sinus EPSCC, demonstrating extensive local invasion and regional lymphadenopathy. The patient presented with nasal obstruction, ocular swelling, visual loss, and multiple neck swellings. Diagnosis was challenging, requiring a multidisciplinary approach and histopathological confirmation. Immunohistochemistry revealed positive cytokeratin AE1/AE3 and synaptophysin markers validating the diagnosis of small cell carcinoma. Conclusion: This case underscores the diagnostic complexities and highlights the importance of swift intervention and a multidisciplinary treatment approach for optimizing patient outcomes in rare and aggressive tumors like EPSCC. Early detection and prompt management are crucial in resource-limited settings to mitigate morbidity and mortality.