Abstract
Extranodal natural killer/T-cell lymphoma (ENKTL) is a rare and aggressive subtype of non-Hodgkin lymphoma, typically involving the nasal cavity. However, it can occasionally present in extranodal sites without nasal involvement, complicating diagnosis. This report describes a 78-year-old man who presented with progressive double vision and visual loss in the right eye over 3 weeks. Examination revealed partial oculomotor nerve palsy with pupillary involvement and signs of optic neuropathy, leading to a diagnosis of orbital apex syndrome. The nasopharyngeal evaluation showed no nasal lesions. Magnetic resonance imaging (MRI) identified diffuse enhancement of the extraocular muscles, intraorbital soft tissues, and optic nerve sheath in the right orbit. A right medial rectus muscle biopsy confirmed extranodal NK/T-cell lymphoma through immunohistochemical analysis. Chemotherapy was initiated, significantly improving both ophthalmoplegia and visual acuity. This case underscores the importance of comprehensive neuro-ophthalmic evaluation and biopsy for diagnosing ENKTL, especially in atypical presentations without nasal involvement. Early detection and treatment are critical for achieving favorable outcomes in this rare disease.