Abstract
An air-fluid border is used as a radiographic sign which evidences a liquid being accumlated in the maxillary sinus.
Though postero-anterior projection and Waters' projection have been usually used to examine a maxillary sinus in a field of rhinology, some reports indicate that the rotational panoramic radiograph are more useful for the detection of maxillary sinus pathosis. However there have been no investigations concerning the air-fluid border on the rotational panoramic radiograph.
The purpose of this study is to analyze the images of air-fluid borders on the rotational panoramic radiographs clinically and to make an experimental confirmation on the image formations of the air-fluid border. Rotational panoramic radiographs of 45 patients were selected for this investigation, whose maxillary sinuses clearly showed the liquid accumlation on the postero-anterior views and/or Waters' views. Radiographic appearances were analyzed and discussed on the various aspects of the air-fluid border such as clearness, shape, a level, superimposed structures on it, comparison with the radiopacity below it and discrimination from thickened mucosa.
Two models of the maxillaly sinus in the different shapes were prepared for the experimental study on the image formation of the air-fluid border. The models with lead wires on those walls were filled with liquid soap and were projected.
Following findings has resulted from the clinical and experimental study.
1. The air-fluid border was detected on all of 45 rotational panoramic radiographs. Twenty-seven of them revealed a continuous line from an anterior to a posterior border of the maxillary sinus. One of them showed a curved line ascending anteriorly, 7 a horizontal line and 19 a curved line ascending posterorly. A downward bulging of the air-fluid border was found just at the zygomatic process in 9 patients with well-developed pneumatized maxillary sinus. An experimental study proved that a lateral margin of the liquid surface was actually projected on a film as the image of the air-fluid border and that the air-fluid border bulged downward at the zygomatic process because the fluid extended into the zygomatic process in the experimental model with prominent pneumatization.
2. On 28 of 45 rotational panoramic radiographs (60.2%), the air-fluid border appeared as a white lines such as a corticated border. Experimental study suggested the posibility that the appearance of the air-fluid border was accounted for by the Mach-band effect.
It was indicated that the rotational panoramic radiograph was one of the most useful method for the detection of the air-fluid border as well as a postero-anterior view and a Waters' view.
