Tomography in Inner and Middle Ear Malformations

Abstract

During the last decade, there has been increasing interest in tomography of temporal bone malformations. More ear malformations are operated upon today, and the indications for operation and for operative technics will depend upon the types of dysplasia present. It is becoming increasingly evident that clinical and audiometric examinations are of limited diagnostic help. X-ray examination of the skull, including special views of the temporal bone, offers only gross information about inner and middle ear abnormalities. Tomography, however, provides much more definitive and clinically useful information. Tomographic examination of ear dysplasias due to thalidomide has shown how polymorphic and extensive ear malformations can be. Since practical devices with plurisectional blurring have been developed, tomography of the skull has made significant progress. The purpose of this paper is to present further diagnostic and surgical experience in a large group of patients and to cite the limits and possible diagnostic errors of tomography. These questions will be discussed on a material of 80 selected cases of congenital hearing defects extensively examined by tomography. Normal Anatomy of the Temporal Bone As Studied by Tomographic Radiographic Means Correct interpretation of abnormal tomograms depends upon an exact knowledge of normal tomography and anatomy of the temporal bone. Detailed anatomic descriptions, including a review of the international literature up to 1958, are given by Mündnich and Frey (21). A more recent American paper was presented by Valvassori in 1963 (29). For examination of ear dysplasias, tomography in sagittal position (anteroposterior view) and with 45° head rotation to the opposite side (Stenvers position without 12° angulation) are sufficient. Cut separation should be 2 mm, although in special questions (e.g., detailed examination of the vestibular or cochlear window) 1 mm may be necessary. Our tomograms were done with the Massiot Polytome. Figures 1 and 2 show normal tomograms in the anteroposterior, and Figures 3 and 4 in the Stenvers projection. The bony labyrinth with the semicircular canals (Fig. 1), the cochlea (Figs. 2 and 3), and internal auditory meatus as well as the tympanic cavity (Figs. 2 and 4), the external auditory meatus, and the mastoid process are well demonstrated. More dimcult are exact visualization and interpretation of the vestibular and cochlear windows and the auditory ossicles. The windows themselves can be barely seen on tomography. Since only bony structures surrounding the windows are visualized, one would better speak of the “niches” of these windows. The niche representing the vestibular window is best shown on the anteroposterior projection (Fig. 1) and the one for the cochlear window on the Stenvers tomogram (Fig. 3). It must be remembered, however, that both niches lie only partially parallel to these tomographic planes.