Analysis of the Expanded Endonasal and Far Medial Transoral Endoscopic Approaches to the Infratemporal Fossa: Feasibility Study for a Multi-Portal Minimally Invasive Approach

Background: Recent advances in endoscopic technology have led to minimally invasive approaches to the infratemporal fossa (ITF), such as endonasal approaches. These obviate some of the morbidity associated with traditional open approaches; however, access to the most lateral regions of the ITF are still limited and often require expanded endonasal or transoral approaches. The expanded endonasal approaches may include contralateral transeptal approach, extended medial maxillectomy, endoscopic Denker approach, or Caldwell-Luc approach, which are associated with their own unique complications. To obviate these associated morbidities, we are proposing a multiportal minimally invasive approach to the ITF which would involve combination of transnasal, transoral, and possibly transfacial approaches. Anatomic perspective is key in successful endoscopic surgery. In this study, we show comparative surgical anatomy between the transnasal and transoral approaches.

Objective: This study aims to compare surgical anatomy from an endoscopic perspective of the far medial transoral approach versus expanded endonasal approach to the ITF. This study also aims to describe the anatomic limitations of each approach. The objective if this study was to describe surgical corridors for a combined endoscopic-assisted approach and in so doing document the anatomic relationships of the key neural, vascular, muscular, and skeletal structures of the ITF.

Methods: A total of eight infratemporal fossae, in four adult human cadaveric specimens, which had been previously injected with red and blue-colored latex, were dissected. Each side underwent a sequential approach to the ITF. A far medial transoral endoscopic approach was initially performed followed by an expanded endonasal approach. Dissection were done under direct visualization using 0, 30, and 45 degree endoscopes. The relationships of critical structures of the ITF were documented with high-definition images using a Storz AIDA system. Image guidance navigation was used to describe limits of dissection.

Results: As anticipated, endoscopic visualization of key anatomic structures in the ITF are significantly different between the two approaches. Both the approaches achieve adequate access to the key structures of the ITF, though visualization and mobility is different between the two approaches. Because of the orientation of the medial and lateral pterygoid muscles, access to the lateral aspect of the ITF is more difficult via the endonasal approach compared with the transoral approach. For the same reason, access to the medial aspect of the ITF is easier using the endonasal approach compared with the transoral approach. Mobility and visualization of key anatomic structures of the ITF is significantly improved when the two approaches are combined.

Conclusion: This cadaveric study provides useful anatomic data in understanding endoscopic perspective between the transoral and transnasal approached in dissecting the ITF. This is a key step in potentially combining two minimally invasive approaches to provide increased visualization, access, and maneuverability in an anatomically complex region. A combination of the two approaches also allows a “two-surgeon, four-hand” technique and may be a viable option to treat select pathology in the ITF.

Image shows combined transoral and transnasal approach: the surgical field is visualized with a 0-degree endoscope transorally while foramen ovale is being instrumented transnasally.