Comparison of different computed tomography post-processing modalities in assessment of various middle ear disorders

Several anatomic structures of the middle ear are not optimally depicted in the standard axial and coronal planes. Several 2D and 3D image-processing modalities are currently available for CT examinations in clinical radiology departments. Till now 3D reconstructions of the temporal bone have not been widely used yet, and attracted only academic interest. The aim of this study was to compare axial (source images), 2D and 3DCT post-processing modalities, and to evaluate the value of 3D reconstructed images/virtual endoscopy (VE) in assessment of various middle ear disorders for identification of the best modality/view for assessment of a particular middle ear structure or pathology. 40 patients with various middle ear disorders, planned for surgical intervention were included in prospective study. Multi-slice CT was performed for all patients. Scans were acquired in the axial plane. The axial source datasets were utilized for generation of 2D reformations and 3D reconstructed images. All studied images were divided into three categories: axial (source images), 2D reformations (MPR and sliding-thin-slab MIP) and 3D reconstruction (virtual endoscopy). The visibility of middle ear structures and pathologies with each modality were scored qualitatively using three-point scoring system in reference to operative findings. Stapes superstructure and footplate, incudostapedial joint, oval and round windows, tympanic segment of the facial nerve and tegmen were not optimally depicted in the axial plane. Sinus tympani and facial recess were best visualized with axial images or VE. 3D reconstruction/VE allowed good visualization of all parts of ossicular chain except stapes superstructure. Regarding pathologic changes, 2D reformations and 3D reconstructed images allowed better visualization of erosion of ossicles and tegmen. 3D reconstruction/VE did not allow detection of foci of otospongiosis. 2D reformations can be considered the mainstay in assessment of most middle ear structures and pathologies. 3D reconstruction/VE seems to provide a useful method for a preoperative general overview of the middle ear anatomy, particularly for the ossicular chain, round window and retrotympanum.