Chronic rhinosinusitis (CRS) is a common medical condition in which inflammation of the lining of the nose and sinuses (airspaces in the skull) causes poor drainage of fluids from the sinuses, leading to nasal congestion, pressure, and pain in the face. In some patients, repeated episodes of inflammation (for example, due to infections or allergies) cause the lining of the sinuses to swell with fluid and protrude as polyps, which may result in more inflammation and further impair drainage.