Poorly Differentiated Non-keratinizing Sinonasal Squamous Cell Carcinoma Masquerading as Chronic Sinusitis: A Case Report.

Sinonasal squamous cell carcinoma (SNSCC) is a rare malignant tumor of the nasal cavity and paranasal sinuses, often presenting with nonspecific symptoms that can delay diagnosis. We report a case of a 50-year-old woman with a poorly differentiated non-keratinizing SNSCC of the left maxillary sinus, initially misdiagnosed as chronic sinusitis for one year. She presented with progressive nasal obstruction and facial pain. Imaging revealed an aggressive maxillary sinus lesion with bony destruction, and an initial biopsy suggested sinonasal undifferentiated carcinoma. The patient underwent left maxillectomy with selective neck dissection; final histopathology confirmed poorly differentiated non-keratinizing SNSCC with lymphovascular invasion but no nodal metastasis. Postoperative recovery was uneventful, and adjuvant radiotherapy was planned. This case underscores the diagnostic challenges of SNSCC and highlights a key clinical lesson that persistent sinus symptoms unresponsive to medical therapy should raise suspicion for malignancy. Early recognition, comprehensive evaluation, and multidisciplinary management are essential for optimal outcomes in patients with aggressive sinonasal tumors.