The most common operation is called functional endoscopic sinus surgery (FESS). This involves a surgeon inserting an endoscope into the nose. The endoscope used for this procedure is a thin rigid instrument that contains lenses. The endoscope allows a detailed magnified view of inside the nose. The surgeon can see the opening of the sinus drainage channels. He or she can then remove any tissues that are blocking the drainage of the affected sinus. This can improve sinus drainage and ventilation and help to restore normal function to the sinus. This operation causes little damage (is minimally invasive). It usually has a high success rate in relieving symptoms of chronic sinusitis.