Stepwise Exposure of the Petrous Carotid. A, Anterior view of a coronal section through the sphenoid and maxillary sinuses, nasal cavity, orbits, and infratemporal fossa. The inferior, middle, and superior concha project medially from the lateral nasal wall. B, The posterior and lateral wall of the maxillary sinus has been removed to expose the pterygopalatine and infratemporal fossae. The pterygoid process of the sphenoid bone forms the posterior wall of the pterygopalatine fossa. The pterygopalatine ganglion is positioned at the anterior end of the vidian canal in the medial part of the pterygopalatine fossa. The maxillary nerve exits the foramen rotundum to enter the pterygopalatine fossa. The maxillary artery passes through the infratemporal fossa and enters the pterygopalatine fossa, where it gives rise to branches that follow the branches of the maxillary nerve. The infratemporal fossa, located below the greater wing of the sphenoid bone, contains the pterygoid muscles and venous plexus, branches of the third trigeminal division, and the maxillary artery. C, The wall of the sphenoid sinus has been removed to expose the cavernous sinus and pituitary gland. The pterygoid processes have been removed to expose the eustachian tube, which opens into the nasopharynx just behind the medial pterygoid plate. The anterior arch of C1 has been removed to expose the odontoid. The clivus has been opened to expose the vertebral and basilar arteries. D, The eustachian tube and floor of the left middle fossa have been removed to expose the upper cervical, petrous, and cavernous carotid. The petrous carotid is positioned behind the fibrous and cartilaginous parts of the eustachian tube, which has been removed. The anterior genu and anterior vertical segment are exposed below and medial to the trigeminal nerve. The greater petrosal nerve passes forward above the horizontal segment and joins the vidian nerve in the area above the foramen lacerum. The trigeminal ganglion and second and third divisions are exposed in the lateral wall of the cavernous sinus. The osseous portion of the eustachian tube is exposed lateral to the posterior genu of the cavernous carotid. (Images courtesy of AL Rhoton, Jr.)