A 48-year-old woman with a 6-month history of chronic rhinosinusitis (CRS) with nasal polyps presents with persistent nasal obstruction and anosmia despite 3 months of topical nasal corticosteroid spray and saline irrigation. Nasal endoscopy confirms bilateral nasal polyps and opacification of the maxillary and ethmoid sinuses. CT PNS shows extensive polypoid disease with sinus opacification. She has no history of asthma or aspirin sensitivity. What is the most appropriate next step in management?