Endoscopic sinus surgery (also called sinoscopy or FESS) is a procedure to remove blockages in the sinuses (the air-filled spaces in the skull bone around the nose). These blockages cause sinusitis, an inflammation of the lining membrane of the sinuses, causing pain and impaired breathing. A thin, lighted instrument with a camera at its tip (an endoscope) is inserted into the nostrils, to view the sinuses. Surgical instruments can then be used along with the endoscope to remove the blockages and improve breathing. The surgery increases the amount of air flowing through the sinuses and allows mucus to drain properly out of the nose. This is usually a day-stay procedure. Endoscopic sinus surgery may also be used to correct a deviated septum (in which the partition separating the left and right sides of the nose is crooked); remove nasal polyps (non-cancerous lumps); or remove tumours.