SURGICAL ANATOMY OF THE EXTENDED MIDDLE CRANIAL FOSSA APPROACH

The extended middle cranial fossa approach includes removal of the pet rous bone from its subtemporal surface in order to expose widely the i nternal auditory canal and the posterior fossa dura around its porus w hile preserving all the important and closely related anatomical struc tures. We have dissected 25 temporal bones and five fresh cadavers in order to define the limits of this approach. Measurements were obtaine d between the different structures to find reliable angles and distanc es that could guide working in this area. A new method of identificati on of the internal auditory canal is discussed based on the measuremen ts taken. The results of the present work showed wide variations in th e different structures. The arcuate eminence was coincident with the s uperior semicircular canal in only 48% of bones. Dehiscence of the gen iculate ganglion and of the internal carotid artery was noted in 16% a nd 20% of specimens, respectively. The angles measured between the dif ferent structures showed great variations. However, the angle between the internal auditory canal and superior petrosal sinus was constant. Though the extended middle cranial fossa is a versatile approach, it a ffords a limited access to the cerebellopontine angle. A thorough unde rstanding of the complex and variable anatomy of this area is necessar y should this approach be utilized.