[Virtual endoscopy of the nasal cavity and the paranasal sinuses with computerized tomography. Anatomical study].

INTRODUCTION Virtual endoscopy is a new 3D technique which permits to depict the inner surface of anatomic cavities. We report our experience in the study of the nasal cavity and paranasal sinuses. MATERIAL AND METHODS CT examinations of the maxillofacial region were obtained using 1.5 or 3.0 mm slices, 1.5 or 3.0 mm table feed, 120 kV, 140 mA, 2 s scan time, standard and high resolution algorithms for bony structures and a field of view of 14-16 cm. The images were transferred on a workstation and processed with the Navigator virtual endoscopy software (General Electric). A threshold value ranging -300 to -550 UH was applied. RESULTS We report a series of virtual images of the nasal cavity which includes rhinopharynx vault, torius tubarius, choanae, turbinates, tubal orifice and osteomeatal complex. Moreover, images of frontal sinus and tear duct, of polyps and fracture of maxillary sinus are also presented. 3D virtual endoscopy provides a clear visualization of the anatomic structures of the nasal cavity and sinuses. The images are similar to those of conventional endoscopy. Moreover virtual endoscopy visualizes the paranasal sinuses, which are not accessible at conventional endoscopy. The main limitations of this new technique are the arbitrary choice of the threshold value and the homogenization of different tissue densities, which reduces the contrast resolution. CONCLUSIONS Virtual endoscopy can presently be considered a complementary technique of the standard axial and coronal CT examination. It provides an effective demonstration of the anatomy of these structures and shows areas which are difficult to visualize with conventional endoscopy. This technique could be of help in didactical activity; its clinical application has to be verified.