18.2.1 Medial Transsphenoidal Approach

If the petrous apex lesion expands into the sphenoid sinus, a medial transsphenoidal approach can be performed. Anatomic landmarks in the sphenoid sinus are shown in Fig. 18.2a . After ethmoidectomies and wide sphenoidotomies ( Fig. 18.2a ), the floor of the sphenoid sinus is drilled posteriorly, using a high-speed drill with a 3-mm coarse diamond burr, until it is flush with the clivus; then a partial clivectomy is performed. Once the medial aspect of the paraclival ICA and the lesion is opened, the thin, small pieces of bone are removed with a 1- or 2-mm Kerrison rongeur to avoid injuring the dura mater, and the cyst is drained into the sphenoid sinus and nasopharynx ( Fig. 18.2b, c ). Angled suction tips facilitate the removal of all granuloma contents as well as the irrigation of the cavity. We advocate inserting a silicone stent into the cavity (e.g., 6–7 mm tracheal T-tube customized in the fashion of a tympanostomy T-tube), draining it into the sinonasal tract, and maintaining the marsupialization of the granuloma for 3 to 6 months.

Lesions that are mainly located posterior to the ICA or that are hard to access because of poor pneumatization require a medial transsphenoidal approach with ICA lateralization. A transpterygoid approach is used to identify the vidian nerve and artery, and to follow them to the anterior genu of the ICA. The posterior nasal and sphenopalatine arteries are dissected and transected, and the pterygopalatine ganglion is exposed. The soft tissues are dissected laterally until the vidian artery and nerve can be visualized exiting their canal ( Fig. 18.2d ). The vidian canal can be identified running on the floor of the sphenoid sinus from medial to lateral in the anteroposterior sagittal plane ( Fig. 18.2e ). The region medial and inferior to the vidian canal is skeletonized with a high-speed drill from anterior to posterior to reach the cartilage of the foramen lacerum ( Fig. 18.2f ). This landmark becomes crucial in avoiding damage to the ICA at this level. The bone over the carotid artery is thinned with the high-speed drill and carefully removed with a combination of drilling and elevation with Kerrison rongeurs, to expose the periosteum that surrounds the vertical and horizontal segments of the ICA ( Fig. 18.2g ). The dura of clivus and the entire medial part of the paraclival ICA are exposed in a similar fashion to provide adequate space to access the lesion ( Fig. 18.2h, i ). Bleeding from the clival bone marrow and basilar plexus can be copious but relatively easy to control with hemostatic paste. Removal of the midclivus and paraclival ICA canal allows the lateralization of the vessel by several millimeters, thus expanding the lateral access to the lesion.