Transtemporal craniotomy and exposure of the right trigeminal nerve. For orientation, anterior is toward the left border of the image; inferior is toward the top border. The temporalis muscle has been divided near the zygomatic arch, anterior to the ear. A large transtemporal craniotomy with elevation of the temporal lobe and division of the tentorium cerebelli has enabled visualization of the middle cranial fossa, the cavernous sinus, the cavernous segment of the internal carotid artery, and components of the trigeminal nerve system. The trigeminal (CNV) nerve leaves the lateral pons, travels in the prepontine cistern before passing over the apex of the petrous temporal bone, and entering Meckel's cave, a CSF-filled dural recess that contains the trigeminal (Gasserian) ganglion. This conduit connects the posterior cranial fossa to the middle fossa. The trigeminal ganglion rests upon the trigeminal impression on the petrous apex medial to the trigeminal prominence, a raised area on the petrous bone. The petrous segment of the internal carotid artery lies medial to the ganglion within the petrous bone. This has been drilled to visualize this relationship as well as to gain exposure to the clivus. From the convex margin of the ganglion arise the ophthalmic (CNV1), maxillary (CNV2), and mandibular (CNV3) divisions. The ophthalmic nerve passes through the superior orbital fissure to the orbit, while the maxillary nerve enters the pterygopalatine fossa through the foramen rotundum. The mandibular nerve passes through foramen ovale to enter the infratemporal fossa. Deep to the trigeminal ganglion is the petrosphenoid ligament which extends from the anteromedial most portion of the petrous bone to the posterior clinoid process. Dorello's canal is bridged by this ligament and contains the abducens nerve and the inferior petrosal sinus. This sinus drains the cavernous sinus to the internal jugular vein. (Image courtesy of PA Rubino)