CT AND MRI OF THE MIDDLE-EAR

High-resolution computed tomography (HRCT) provides excellent contrast between osseous structures, air and soft tissue in conjunction with h igh spatial resolution. Therefore, thin-section HRCT with bone window setting is the method of choice for the examination of the middle ear structures. The indications are acute and chronic inflammatory changes , cholesteatoma and tumor, the ''postoperative middle ear,'' and malfo rmations. In most cases, HRCT enables differentiation between inflamma tory changes, cholesteatoma, and tumor. The excellent depiction of sub tle osseous details enables the identification of erosions of the ossi cles or of the bony walls of the mastoid cells, of osseous defects of the tegmen, of the bony labyrinth, and of the tympanic course of the f acial canal. In addition, HRCT enables excellent depiction of reconstr uctions of the ossicles or prosthesis of the ossicles. Although HRCT i s the first method of choice, magnetic resonance imaging (MRI) may pro vide additional information and lead to a more accurate diagnosis in s ome cases. This is explained by the excellent soft tissue contrast pro vided by MRI. In addition, MRI offers the possibility of using various pulse sequences and the administration of IV contrast material. There fore, MRI may allow the differentiation between inflammatory changes, cholesteatoma, and tumor in those cases in which accurate diagnosis ca nnot be made by HRCT. The differentiation between a meningocele or men ingoencephalocele and other entities such as tumors or cholesteatoma c an be established by MRI. Furthermore, MRI can accurately depict cases of labyrinthitis or of neuritis of the facial nerve or of intracrania l disease caused by middle ear processes, while this is not always pos sible by HRCT. In summary, HRCT of the middle ear is the method of cho ice, but MRI may provide supplementary information in those cases in w hich accurate diagnosis cannot be established by HRCT.