Background
: Recently many otolaryngologists use OMU CT(Ostiomeatal unit CT) scan to diagnose chronic sinusitis because PNS plain radiograph has many limitations to perform detailed anatomic examination about ostiomeatal unit. But many primary physicians have depended on plain radiograph to diagnose chronic sinusitis due to high medical cost and accessibility problem. In this study, I compared plain radiograph with OMU CT to know how accurately plain radiograph diagnose and localize the residual sinus diseases.

Methods : I performed a prospective study of 71 patients who were clinically suspected to have a chronic sinusitis. all patients in this study had conventional sinus radioraph and OMU CT. Two examinations were performed on the same day. Before undertaken two examinations, all patients completed a qestionnaire which was accociated with symptoms of chronic sinusitis. The plain radiograph was interpreted by two radiologists and OMU CT were interpreted independently of the plain radiograph.

Results : Of the 71 patients studied, 40 were men and 31 women. Their ages ranged from 15 to 67 years. There is no significant symptom difference between normal and abnormal OMU CT group. With respect to the location of sinusitis, maxillary sinus was most common site and then ethmoid, sphenoid, frontal sinus in sequence. Validity of plain radiograph is as follows : sensitivity 75.5%, specificity 61.1%, positive predictive value 85.1% and negative predictive value 45.8%. Validity of plain radiograph by each sinus shows some difference acording to the sinus (Table 6). Sensitivity is relatively high in maxillary sinus(About 79% and 68% in right and left) but others low(Below 50%). Specificity is almost over 90% except maxillary sinus.

Conclusion : Chronic sinusitis often underdiagnosed or overdiagnosed on the finings of plain radiograph. But considering health care cost and acessibility PNS plain radiograph is still useful diagnositc modality in primary care.