Complex sentence: Functional endoscopic sinus surgery (FESS) is the mainstay in the surgical treatment of sinusitis and nasal polyps, including bacterial, fungal, recurrent acute, and chronic sinus problems.
Split into simpler sentences: Functional endoscopic sinus surgery (FESS) is a surgical modality for some diseases of the nose and paranasal sinuses. It is the mainstay in the surgical treatment of sinusitis and nasal polyps, including bacterial, fungal, recurrent acute, and chronic sinus problems.