Transtemporal approach to the skull base: an anatomical study.

The surgical anatomy of a transtemporal approach to the structures of the clivus was defined with the aid of dissections in 10 cadaver heads. The steps in the dissection consisted of first exposing the cervical internal carotid artery (ICA), the internal jugular vein, and the caudal cranial nerves, each at the skull base; then performing small retromastoid and temporal craniotomies; and, finally, drilling away the petrous and tympanic bone to expose the intratemporal parts of the facial nerve, the petrous ICA, the sigmoid sinus, and the jugular bulb. To expose the structures of the lower clivus, the sigmoid sinus was ligated and divided, the facial nerve was displaced anterosuperiorly, and the inner ear structures were preserved. Dural opening exposed the anterolateral and anterior surfaces of the medulla, the pontomedullary junction, and the spinomedullary junction. The ipsilateral vertebral artery and often the contralateral vertebral artery and the vertebrobasilar junction, the caudal cranial nerves, and the origin of the 6th, 7th, and 8th cranial nerves were well exposed. To expose the structures of the middle clivus, we drilled away the labyrinth, the cochlea, and a portion of the clival bone. The facial nerve was displaced posteroinferiorly. Dural opening exposed the ipsilateral anterior surface of the pons, the midbasilar artery, and the ipsilateral 5th, 6th, 7th, and 8th cranial nerves. A portion of the contralateral anterior surface of the pons was also exposed at times. The superior limit of this exposure was just above the origin of the trigeminal nerve. The exposure of the upper clival structures was limited with this approach, and required medial temporal lobe retraction. Two case reports are included to illustrate the application of the transtemporal approach to the exposure and clipping of aneurysms of the vertebrobasilar system. The advantages and disadvantages of this approach are discussed.