Classification and quantification of the petrosal approach to the petroclival region

Object. The petrosal approach to the petroclival region has been used by a variety of authors in various ways and the terminology has become quite con fusing. A systematic assessment of the benefits and limitations of each app roach is also lacking. The authors classify their approach to the middle an d upper clivus, review the applications for each, and test their hypotheses on a cadaver model by using frameless stereotactic guidance. Methods. The petrosal approach to the upper and middle clivus is divided in to four increasingly morbidity-producing steps: retrolabyrinthine, transcru sal (partial labyrinthectomy), transotic, and transcochlear approaches. Fou r latex-injected cadaveric heads (eight sides) underwent dissection in whic h frameless stereotactic guidance was used. An area of exposure 10 cm super ficial to a central target (working area) was calculated. The area and leng th of clival exposure with each subsequent dissection was also calculated. The retrolabyrinthine approach spares hearing and facial function but provi des for only a small window of upper clival exposure. The view afforded by what we have called the transcrusal approach provides for up to four times this exposure. The transotic and transcochlear procedures, although produci ng more morbidity, add little in terms of a larger clival window. However, with each step, the surgical freedom for manipulation of instruments increa ses. Conclusions. The petrosal approach to the upper and middle clivus is useful but should be used judiciously, because levels of morbidity can be high. T he retrolabyrinthine approach has limited utility. For tumors without bone invasion, the transcrusal approach provides a much more versatile exposure with an excellent chance of hearing and facial nerve preservation. The tran sotic approach provides for greater versatility in treating lesions but cli val exposure is not greatly enhanced. Transcochlear exposure adds little in terms of intradural exposure and should be reserved for cases in which acc ess to the petrous carotid artery is necessary.