Diplopia and Exophthalmos As Clinical Manifestations of Sinonasal Undifferentiated Carcinoma: A Case Report.

Sinonasal undifferentiated carcinoma (SNUC) is a rare and highly aggressive epithelial malignancy with an incidence of 0.2 per 100,000 individuals, often presenting at advanced stages due to nonspecific sinonasal symptoms. Orbital involvement may serve as an important early clinical clue in its diagnosis. A 72-year-old man presented with progressive unilateral exophthalmos, excessive lacrimation, and intermittent diplopia. Imaging revealed an extensive sinonasal mass with orbital involvement. Histopathologic evaluation confirmed the diagnosis of SNUC of the ethmoid sinus, classified according to the American Joint Committee on Cancer 8th edition staging system for sinonasal malignancies as cT4N0M0 (Stage IVA). Due to extensive local invasion with orbital involvement, multidisciplinary consensus favored induction chemotherapy followed by definitive concurrent chemoradiation rather than surgical resection in an effort to preserve orbital function and avoid significant operative morbidity. The patient was treated with induction chemotherapy followed by definitive concurrent chemoradiation, resulting in a complete radiographic and metabolic response. At long-term follow-up, he remains disease-free with manageable treatment-related toxicities. This case highlights the importance of recognizing orbital symptoms as early manifestations of SNUC. It supports the role of induction chemotherapy as part of a multimodal treatment strategy for locally advanced disease.