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Lateral View of Pons, Trigeminal Nerve, and Cavernous Portion of Internal Carotid Artery

Surgical Correlation


Lateral view of pons, trigeminal nerve, and cavernous portion of internal carotid artery. The lateral surface of the pons shows emergence of the trigeminal nerve with its larger sensory root and smaller motor root. The nerve passes over the petrous apex to expand within Meckel's cave as the Gasserian ganglion. The ganglion gives rise to three divisions, the ophthalmic, maxillary, and mandibular nerves. The ophthalmic and maxillary nerves are sensory only; the motor root joins the mandibular nerve near the foramen ovale as a mixed nerve. The trochlear nerve courses forward from the dorsal surface of the midbrain and enters the lateral wall of the cavernous sinus where it lies superior to the ophthalmic nerve (the cavernous segment of the internal carotid artery is located within the cavernous sinus). Both nerves enter the orbit through the superior orbital fissure. The maxillary nerve enters the pterygopalatine fossa through the foramen rotundum. The mandibular nerve enters the infratemporal fossa through the foramen ovale and gives rise to multiple branches including the buccal, lingual, inferior alveolar, and auriculotemporal nerves. The foramen spinosum is located slightly posterolateral to the ovale and transmits the middle meningeal artery. The facial and vestibulocochlear nerves emerge from the pons near the pontomedullary junction and cerebellopontine angle and enter the internal auditory meatus of the petrous temporal bone. The nerves in this specimen are separated by a loop of the anterior inferior cerebellar artery, a branch of the basilar artery. At the distal end of the canal the facial nerve courses between the cochlea anteriorly and the semicircular canals posteriorly. Here, the facial nerve ends at the geniculate ganglion, a sensory ganglion, from which arises the greater superficial petrosal nerve carrying preganglionic parasympathetic fibers to the pterygopalatine ganglion via Vidian's canal. The facial nerve (tympanic segment) continues posteriorly into the facial canal along the medial wall of the middle ear cavity below the lateral semicircular canal. Beyond the pyramidal eminence the nerve turns inferiorly as the mastoid segment along the posterior wall of the cavity. Here, it gives rise to the chorda tympani branch which courses forward from the posterior wall to the anterior wall passing between the malleus and incus bones. It carries taste fibers from the anterior two-thirds of the tongue and preganglionic parasympathetic fibers to the submandibular ganglion. The basilar artery ascends near the pons midline. Its superior cerebellar arterial branches course posteriorly in a subtentorial direction to supply the superior aspect of the cerebellum.  (Image courtesy of PA Rubino)