Stepwise Exposure of the Petrous Carotid in the Postauricular Transtemporal Approach. A, The incision sweeps widely around the posterior margin of the ear (inset). The scalp flap has been reflected forward, the external auditory canal transected, the parotid gland removed, and a mastoidectomy completed to expose the semicircular canals and the mastoid segment of the facial nerve. The neck dissection exposes the internal jugular vein, vertebral artery, and Cranial Nerves IX to XII. The internal jugular vein exiting the jugular foramen and the cervical carotid ascending to enter the carotid canal are exposed after removal or downward displacement of the mandibular condyle. B, The external auditory canal has been resected to expose the structures in the tympanic cavity and the promontory overlying the basal turn of the cochlea. The posterior genu of the petrous carotid is located medial, anterior, and inferior to the promontory and cochlea. The tympanic segment of the facial nerve courses below the lateral semicircular canal. The chorda tympani arises from the mastoid segment of the facial nerve and passes forward along the upper part of the malleus to enter its anterior canaliculus. The tendon of the tensor tympani muscle is positioned superior to the eustachian tube, and both are positioned anterior to the petrous carotid. C, A frontotemporal craniotomy has been completed and the floor of the middle cranial fossa removed. The incus and malleus have been removed while preserving the stapes and the tensor tympani muscle. The posterior genu of the petrous carotid is exposed below and medial to the promontory, which overlies the basal turn of the cochlea. D, The tensor tympani has been removed. The cochlea sits deep to the promontory above the posterior genu of the petrous carotid. The semicircular canals have been exposed above the jugular bulb. The stapes has been removed from the oval window. The segment of the maxillary nerve and artery crossing the pterygopalatine fossa has been exposed. The membranous wall of the eustachian tube has been opened to expose the tube’s opening into the nasopharynx. The eustachian tube descends across the anterior surface of the horizontal segment to reach the nasopharynx. The vidian nerve has been exposed. (Images courtesy of AL Rhoton, Jr.)