False-colour X-ray of the face of a person suffering from sinusitis, an inflammation of one of the paranasal sinuses. In this case one of the maxillary sinuses is inflamed; it appears as an enlarged orange patch at right. The paranasal sinuses are air spaces located within the facial bones. They are lined with mucous membranes and connect with the nose. The maxillary sinuses lie within the maxilla (upper jaw bone). The secretion of mucus in the sinuses acts as a trap against microorganisms & foreign particles. Sinusitis is often caused by infection spreading from the nose. Symptoms include headache & soreness and a discharge may be passed through the nose.