Sino-nasal B cell lymphoma is an uncommon malignancy which is difficult to diagnose. A 66-year-old male presented with left orbital pain and swelling which were unresponsive to 2 weeks of antibiotic treatment. Nasal endoscopy revealed no specific finding in both nasal cavities. CT scans of paranasal sinuses demonstrated whole soft tissue density with bony erosion in the left frontal and ethmoid sinus. Lamina papyracea and orbital content were displaced laterally by the frontal sinus mass. MRI

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... owed no direct invasion to the anterior cranial fossa or the orbit. Biopsy of the frontal sinus mass was confirmed as a diffused large B-cell lymphoma. The patient was successfully treated with chemotherapy.