define sinusitis
Medical Definition of Sinusitis Our Sinus Infection (Sinusitis) Main Article provides a comprehensive look at the who, what, when and how of Sinus Infection (Sinusitis) Sinusitis: Inflammation of the lining membrane in any of the hollow areas (sinuses) of the skull around the nose. Sinusitis may be caused by anything that interferes with air flow into the sinuses and the drainage of mucous out of the sinuses. The sinus openings, called ostia, may be obstructed by swelling of the tissue lining the ostia and adjacent nasal passage tissue; for example, from colds, allergies, and tissue irritants (nasal sprays, cocaine, cigarette smoke).