Occasionally, infectious agents enter the maxillary antrum from infected dental roots. In the majority of these infections, pathogens are gram-positive bacteria. The maxillary sinus is most commonly involved, followed in frequency by the frontal, ethmoid, and sphenoid sinuses. Sinus infection results in swelling of the mucous membranes and copious mucoid secretions. In a poorly draining sinus, these secretions are good culture media and can rapidly become purulent.
Acute sinusitis has radiographic features that distinguish it from allergic sinusitis.
In acute sinusitis, the thickened mucosal margin is smooth rather than scalloped and follows the contour of the sinus walls. Air-fluid levels are the hallmark of infectious sinusitis. Infections are often confined to a single sinus but may also involve the ipsilateral maxillary, frontal, and ethmoid sinuses owing to some obstructive process in the middle meatus. A pansinusitis usually represents an infectious complication of an allergic sinusitis. Polyp formation is not a feature of infectious sinusitis.