 Sinus surgery is a common procedure. A potential complication is injuring the membranes of the brain. This can lead to leakage of brain fluid through the nose. We would like to estimate the incident rates of that complication. At the end of the operation, a thin gauze is inserted into the nose on both sides in addition to the usual tampon. This gauze will be analyzed at the laboratory for beta-2-transferrin, which is a biomarker for brain liquid. 