[CT and MRI of the petrous bone].

Diseases of the petrous bone should now be diagnosed by means of high-resolution multislice spiral computed tomography (MSCT) and/or magnetic resonance imaging (MRI). The first step in the process of diagnosis, however, must be conventional X-ray photographs (according to Schüller, Mayer, Stenvers) for screening purposes, because of the high cost of the other procedures mentioned. Because of the excellent imaging of bone structures with MSCT, this technique is especially suitable for the diagnosis both of acquired pathologies and of congenital abnormalities of the external auditory meatus, the middle ear and the mastoid, of trauma-induced pathologies of the entire petrous bone, and of osteogenic diseases. MRI is the method of choice for examination of the labyrinthine system, the interior auditory meatus and the cerebellopontine angle because it gives much the best depiction of soft tissue. Sometimes when questions remain unsolved after computed tomography (CT) examination of the middle ear MRI can be applied to complement CT, and it can yield additional information. Lesions affecting the apex of the petrous pyramid should be examined by MRI. High-resolution CT through the bone window and thin-layer MRI are both components of the presurgical diagnosis before cochlear implant (CI) surgery. For postoperative monitoring a conventional transorbital X-ray of the petrous bone is sufficient; CT is indicated only in complicated cases, and MRI is absolutely contraindicated after CI.