Sinusitis in cattle generally involves the frontal sinus, with the maxillary sinus rarely being affected. The most common cause of a frontal sinusitis is dehorning. Other less prevalent causes are injuries to the horn with hemorrhage into the sinus, extension of infection from -the nasal mucous membranes, as well as contusions and fractures of the bones of the frontal sinus area. Malignant head catarrh and purulent rhinitis of calves have sinusitis as 'a secondary symptom.