Inflammation of the mucosal lining of a SINUS, usually the sinuses in the face. Most cases occur as a result of infection spreading from the NOSE and usually follow a viral infection of the upper respiratory tract. Treatment is not always necessary but ANTIBIOTICS and VASOCONSTRICTORS may be advised. Surgery to drain the sinuses is sometimes necessary in severe cases. Rarely it may lead to cerebral ABSCESS or THROMBOSIS of one of the venous sinuses in the brain (see BRAIN).