10 The Endoscopic Transpterygoid Approach to the Parasellar and Infratemporal Fossa
Alexandre B. Todeschini, Bradley A. Otto, Ricardo L. Carrau, and Daniel M. Prevedello
Abstract
The pterygopalatine and infratemporal fossa, as well as the paraclival structures such as Meckel’s cave, cavernous sinus, and superior orbital fissure, represent a challenging surgical area, particularly using conventional skull base approaches which require highly invasive and aggressive lateral corridors. The expanded endoscopic endonasal approach creates an anteromedial corridor to the pterygopalatine and infratemporal fossae, which we will describe here, avoiding any brain retraction or manipulation.
We describe and review here the anatomical landmarks for a modular approach, using the petrous internal carotid artery (ICA) as the main landmark to create a safe approach to the pterygopalatine fossa. The different zones which can be approached through this technique are: zone 1: medial petrous apex; zone 2: petroclival approach; zone 3: quadrangular space/Meckel’s cave approach; zone 4: superior cavernous sinus approach; and zone 5: transpterygoid and infratemporal approach. We have also added zone 6, related to the occipital condyle, and zone 7, related to the exposure of the jugular foramen.
A successful transpterygoid approach is dependent on a steep learning curve of endoscopic endonasal surgery, which has the coronal plane approaches at its final step. Only after being intimately familiarized with the anatomy and techniques of endoscopic surgery should such approaches be attempted.
Keywords: Keywords: skull base, neurosurgery, otolaryngology, endoscopy, pterygopalatine fossa, endoscopic endonasal approach
10.1 Introduction
The pterygopalatine and infratemporal fossa, as well as the paraclival structures such as Meckel’s cave, cavernous sinus, and superior orbital fissure, represent a challenging surgical area, particularly using conventional skull base approaches which require highly invasive and aggressive lateral corridors with extensive muscle manipulation and bone removal increasing the risk of postoperative complications such as muscle atrophy and retraction, pain, and aesthetic defects.1 , 2 , 3 , 4 The lateral approach also implies working through narrow windows across and between nerves and vessels (the most critical being the petrous internal carotid artery [ICA]) increasing the risk of sequelae from the procedure and making these approaches a challenge even for experienced skull base surgeons. The use of the anteromedial corridor to the coronal plane was not possible when using microscope assisted techniques, due to the limited lateral vision and reach that the nasal speculum and the microscope provided. The use of the endoscope, eliminating the nasal speculum, and adding the angled endoscopes allowed the development of the expanded endoscopic endonasal approach which includes the coronal plane, with a greater lateral reach using the transpterygoid approach, creating an anteromedial corridor to the pterygopalatine and infratemporal fossae, which we will describe here, avoiding any brain retraction or manipulation.5 , 6 , 7
In 1999, Bolger and Osenbach8 first described their successful experience in treating a cerebrospinal fluid (CSF) leak and encephalocele from a bony defect in the lateral recess of the sphenoid sinus using some of the tenets of this approach. Since then other notable neurosurgeons and ear, nose, and throat (ENT) surgeons have worked together and described the anatomical landmarks and endonasal route to this area. The 2005 papers by Cavallo et al6 and by Kassam et al5 which describe, respectively, the anatomical landmarks and a modular approach to five different areas, using the petrous ICA as landmark, aided by the increasing presence of image guidance systems, allow a safe approach to the pterygopalatine fossa in experienced hands. In this chapter, we have included two further zones.
10.2 Anatomical Landmarks and Surgical Strategies
The exposure for a transpterygoid approach starts with the resection of the right middle turbinate, lateralization of the left middle turbinate, and out fracture of the inferior turbinate bilaterally. Resecting the remaining turbinate may be done for a better workspace; however, it may lead to disruption of the normal air flow in the nose. We recommend elevating a pedicled nasoseptal flap for reconstruction at the end of the case. This must be elevated from the contralateral side of the approach to make sure the arterial pedicle will be preserved.9
Afterwards, a posterior nasal septectomy, wide bilateral sphenoidectomies, and posterior ethmoidectomies are done. The basopharyngeal fascia is then stripped away from the undersurface of the sphenoid floor (Fig. 10.1), which is drilled flush with the clival recess. Next, the vessels emerging from the sphenopalatine foramen (sphenopalatine and posterior nasal arteries) are isolated and coagulated (hence, the contralateral nasoseptal pedicle) (Fig. 10.2). A posterior maxillary antrostomy is performed and the medial pterygoid plate can be identified after lateralization of the contents of the pterygopalatine fossa (Fig. 10.3) keeping the periosteum intact. The palate-vaginal vessels and nerve are transected to allow lateralization of the pterygopalatine fossa. At this point, the vidian nerve and artery bundle can be clearly seen originating from the vidian canal along the base of the pterygoid plates, which can be further confirmed by image guidance, usually at the insertion of the middle pterygoid plate on the pterygoid process of the sphenoid bone.5 , 7 , 9
Fig. 10.1 Striping the basopharyngeal fascia from the undersurface of the sphenoid to drill the floor.
Fig. 10.2 After the initial steps of the dissection the sphenopalatine artery was sectioned and a maxillary antrostomy was done. A partial removal of the posterior maxillary exposes the maxillary artery and V2 as it transitions into the infraorbital nerve. The pterygopalatine fossa contents, including the ganglion, are seen posterior to the sphenopalatine artery.
Fig. 10.3 Lateralizing the contents of the pterygopalatine fossa, the vidian canal can be seen extending posteriorly from the fossa.
The most critical landmark for transpterygoid approaches is the petrous ICA, and the vidian canal is the guide to identify it. The vidian canal can be found by following the sphenoid floor from a medial to lateral direction, located at the junction of the sphenoid floor as it disappears laterally and transitions with the medial pterygoid wedge. Once identified, drilling can proceed cautiously along its inferior and medial aspect since the ICA is located along the superior margin of the vidian canal (Fig. 10.4). Once the depth at which the ICA is located has been established, the superior lateral and medial bone portions can be removed. Once the anterior genu of the ICA is exposed, where the vidian artery consistently emerges from its lower margin, one can safely proceed with dissection.7
Fig. 10.4 With careful drilling following the vidian canal posteriorly, we can locate the anterior genu of the internal carotid artery. A dense fibrous tissue is usually seen around it.
The five modules described by Kassam et al5 relate to the course of the petrous ICA: zone 1: medial petrous apex; zone 2: petroclival approach; zone 3: quadrangular space/Meckel’s cave approach; zone 4: superior cavernous sinus approach; and zone 5: transpterygoid and infratemporal approach. It is useful to divide these into two general categories in relation to the horizontal segment of the petrous ICA, as infrapetrous (zones 1 and 2) and suprapetrous (zones 3, 4, and 5). We have also added zone 6 related to the occipital condyle and zone 7, which is related to the exposure of the jugular foramen. The removal of the Eustachian tube improves visualization on the exposure of zones 6 and 7.
The exposure and dissection steps described above are usually needed for all seven modules. According to the case at hand, a more complex and extensive exposure may be required.
10.2.1 Zone 1: Medial Petrous Apex (Infrapetrous)
The initial steps described above should present the surgeon with the anterior genu of the ICA and ample exposure of the sphenoid sinus and posterior maxillary wall. For a medial petrous apex lesion, where the lesion has expanded into the apex and created a window into the lateral recess of the sphenoid sinus, direct access to the lesion medial to the ICA is possible. If such window has not been created by the lesion, the bone over the anterior genu of the ICA and lateral to it is drilled to eggshell thinness and removed to allow the carotid to be moved laterally without occluding or compressing it in the carotid canal. Once moved, the underlying petrous apex can be accessed. For a better medial exposure, a portion of the clivus may be drilled below the level of the genu to avoid the paraclival ICA (Fig. 10.5).
