[Virtual endoscopy with computed tomography of the anatomical structures of the middle ear]

We applied the new technique of virtual endoscopy to the middle ear because this anatomical area is characterized by favorable contrast.

CT examinations of the petrous bone were obtained using 1.5 mm thick 1 coronal axis slices, with 1 mm or 1.5 mm table feed, 120 kV, 140-170 mA and 2 s scan time. The images were reconstructed with the high resolution algorithm for bony structures and a small field of view (9.6 cm), separately for the right and left petrous bone. The images were then transferred on a workstation and processed with the Navigator virtual endoscopic software (General Electric). A threshold value ranging -350 to -600 HU was applied.

A series of images is acquired as the virtual endoscope moves from the external auditory canal to the middle ear cavity. Images of the anterior, medial, and posterior surfaces of the middle ear are presented. Different views of the ossicles are also presented. High quality images were always obtained for the middle ear structures, including the ossicles. CT endoscopy of the middle ear provides a new view of the anatomy of this complex area. It has some advantages and disadvantages; the former can be summarized as follows: -demonstration of areas which are difficult to show with endoscopy because of the presence of membrana tympani; -the virtual endoscope can be placed in several positions and therefore it can be inserted in all sites and tortuous places of anatomical cavity; -nice and effective demonstration of the ossicular chain including the stapes. The disadvantages are related to the fact that the endoscopic reconstruction (such as any other three-dimensional reconstruction) is a representation of surfaces where different densities are necessarily homogenized.

CT virtual endoscopy of the middle ear can currently be considered a complementary technique to conventional CT because it permits better anatomical detailing of this complex region.