COMPUTERIZED TOMOGRAPHIC-IMAGES OF SECOND ARY CHOLESTEATOMAS OF THE MIDDLE-EAR AND THE PETROUS BONE

The authors present their experience of secondary cholesteatomas of th e middle ear explored by computerized tomography (CT). Following a bri ef anatomicopathological description of secondary petrous bone cholest eatomas, and of the CT technique used for their exploration, they desc ribe and illustrate the classical ''bag-shaped'' internal or external attical forms usually extended to the antrum and the mastoid process, and the less common locations often due to relapse or postoperative re currences (anterior hypotympanic or posterior mastoidal). The holotymp anic forms, usually due to ''lamellar'' cholesteatomas, create diagnos tic problems with other opacities in the cavity, as also do certain fo rms that are evacuated spontaneously or by aspiration. One of the qual ities of CT lies in the preoperative extension assessment. The lesion may extend towards the internal wall of the cavity (lateral semicircul ar canal, second portion of the facial nerve), towards the labyrinth t o the petrosal apex and/or the geniculate ganglion, and above all towa rds the inferior labyrinth which might bring the cholesteatoma into co ntact with large vessels (e.g. jugular vein bulb for postero-inferior extensions, carotid canal for antero-inferior extensions). Extension i nto anfractuosities of the cavity walls (sinus tympani, subratubal fos sette) must be systematically looked for in order to avoid postoperati ve recurrences. The value of CT in the search for postoperative compli cations (brain abscess, thrombophlebitis) is described and illustrated . The value and rank of MRI are discussed in problems of differential diagnosis with other occupying processes of the cavity (glomic tumour, neurinoma, etc.) and in the presence of postoperative opacities where MRI can sometimes differentiate between simple opacity of inflammator y origin (effusion, fibrosis), cholesterol granuloma and cholesteatoma s, bearing in mind that these lesions may coexist and that they are di fficult to diagnose. The authors conclude that computerized tomography is useful for preoperative assessment in surgery of middle ear choles teatomas before each of the two stages of tympanoplasty.