Inflammatory and Allergic Sinus Disease

Abstract

Acute sinusitis is most often due to secondary bacterial infection following an upper respiratory tract infection of viral origin. Infection can also occur in the maxillary antrum by secondary extension from an infected tooth in the upper jaw. The primary site of infection is the lining mucosa of the sinus. The accompanying oedematous swelling of the mucosa will show on the radiograph as an opaque rim around the periphery of the sinus. It is said that in infective sinusitis the rim of mucous membrane follows the contour of and is parallel to the walls of the sinus — in contradistinction to allergic sinus disease in which the mucosa assumes a polypoid aspect with a convex inner border. This distinction is by no means clear-cut, however, and does not always co-relate well with the findings at antroscopy and mucosal biopsy. Acute sinusitis is accompanied by an outpouring of fluid into the sinus cavity causing a total loss of translucence in the affected sinus on the radiograph. This is a nonspecific sign and, although in the vast majority of patients it denotes infection, a sinus filled with blood or new growth could give a similar appearance. More certain evidence of infection is provided radiologically when there is a fluid level (always assuming that there has been no trauma or recent antral washout). It is important for the demonstration of fluid levels that all sinus radiographs are taken with the patient in an upright position with a horizontal X-ray beam; if there is any doubt about the presence of fluid a tilted view should be obtained (Fig. 5.1), which will lead to a new horizontal level. It should be remembered that thick viscid pus or mucus may require a few moments to assume a new level when the head is tilted. In many patients the upright lateral view of the sinuses shows a fluid level most obviously. Although fluid levels can be adequately demonstrated in all the sinuses on plain radiographs, they are often more obvious on CT scan. They may also be shown by magnetic resonance studies, when the fluid in the sinus cavity and the thickened mucosa give a characteristically strong signal on T₂-weighted spin echo sequences (Figs. 5.2, 5.3 and 5.4).