False-colour x-ray of the front of the head of a person suffering from sinusitis, the inflammation of the paranasal sinuses (the mucous-filled air spaces situated above the eyes in the facial bones appearing enlarged & orange in the image) that connect with the nose. Mucous production serves as a protection agains microorganisms & foreign particles. Sinusitis is often caused by infection spreading from the nose; symptoms include headache & soreness & a discharge may be passed through the nose. Since the walls of the sinuses are so thin, infection may spread to the protective layers around the brain (meninges), leading to potentially severe meningitis.