Practical Surgical Landmarks for the Planning of a Transpterygoid Endoscopic Endonasal Approach

Background: Endoscopic endonasal approaches (EEA) to the skull base are based on the principle of using anatomical corridors to access a region of interest. We define a transpterygoid approach as one requiring the partial or complete removal of the pterygoid process. Transpterygoid (TP) approaches include those that access the lateral recess of the sphenoid sinus, the foramen lacerum or petrous ICA, Meckel's cave or cavernous sinus, lateral nasopharynx (fossa of Rosenmüller), and infratemporal fossa.

Methods: We investigated different variations of the TP-EEA using a previously described cadaveric model. Fresh specimens were dissected endonasally using endoscopic instruments and surgical navigation for correlation with the multiplanar images.

Results: The TP-EEA field may be divided by vertical and horizontal lines that cross the vidian and rotundum foramina. These lines divide the possible approaches as follows: Type A is an approach that is limited to the base of the pterygoid plates above the level of the vidian canal, and is indicated for lesions such as CSF leaks of the Sternberg canal. Type B involves the dissection of the vidian canal removing the base of the pterygoid plates to reach the petrous apex (infra- or retro-petrous), Meckel's cave, or, rarely, the cavernous sinus (zones 1, 2, 3, and 4, respectively). Type C is an extended approach to the pterygopalatine fossa involving partial removal of the medial or lateral pterygoid plates, such as that required for the transposition of a temporoparietal fascia flap. Type D provides access to the infratemporal fossa and may or may not require removal of the plates (zone 5). Type E provides exposure of the lateral nasopharynx (fossa of Rosenmüller) and requires the removal of the medial or both pterygoid plates and the medial third of the eustachian tube. Vertical and horizontal lines intersecting at the vidian and rotundum foramina help to estimate the extent of the approach. In general, lesions above the vidian foramen and medial to foramen rotundum can be exposed with a wide nasoantral window and removal of the posterior wall of the antrum. Lesions below the vidian foramen and/ lateral to the foramen rotundum require a medial maxillectomy and removal of the lateral wall of the maxillary sinus.

Conclusions: A safe and effective transpterygoid approach requires an experienced surgeon who is familiar with the complex endoscopic anatomy of the region. The exposed landmarks are useful for the preoperative planning as well as for intraoperative orientation.