Rare Complications of Chronic Rhinosinusitis Associated With Nasal Polyps and Osseous Metaplasia.

Chronic rhinosinusitis with nasal polyps (CRSwNP) is typically a benign condition; however, osseous metaplasia (OM), skull base erosion, and intracranial extension are rare complications, especially in young patients. Reporting such cases is important to increase awareness of unusual presentations of CRSwNP and guide management. We report the case of an 18-year-old male with a history of asthma and prior polypectomy who presented with worsening frontal headaches, subtle visual changes, and right eye proptosis. Imaging revealed extensive pansinusitis with complete frontal sinus opacification, bony erosion of the anterior skull base, and evidence of intracranial and orbital extension. The patient underwent endoscopic sinus surgery, which revealed fibrotic polyps, bone expansion, and purulent intracranial collections. Cultures were obtained, and decompression of the frontal sinuses was accomplished through bilateral Draf IIb procedures. Postoperatively, the patient experienced resolution of proptosis and improvement of symptoms. This case highlights an unusual and aggressive course of CRSwNP complicated by features of OM and emphasizes the importance of early recognition, multidisciplinary management, and close follow-up in preventing neurological and ophthalmic sequelae.