Infraorbital Nerve: A Road Map to the Pterygopalatine Fossa, Cavernous Sinus, and Skull Base in Endoscopic Transmaxillary Approaches

Introduction: Endoscopic transmaxillary approaches are becoming more commonly performed for pathology of the anterolateral skull base, including the cavernous sinus, pterygopalatine fossa, and infratemporal fossa. This is an anatomically complex region which contains branches of the trigeminal nerve, external carotid artery, and is in close proximity to the internal carotid artery. Intraoperatively, we have found the infraorbital nerve (ION) located within the roof maxillary sinus to be an easily identifiable landmark that leads to the skull base. In this study, we sought to study the anatomy of the ION and describe its relationship to other neurovascular structures encountered in endoscopic transmaxillary approaches.

Materials and Methods: Endoscopic anatomical dissections were performed in four silicon-injected/formalin-fixed cadaveric heads bilaterally (eight sides). Endonasal transmaxillary and direct transmaxillary approaches were performed, and anatomical correlations were analyzed and documented. Stereotactic imaging was performed on each specimen to correlate landmarks and enable precise measurement for each segment.

Results: Anatomical dissections of the ION and maxillary nerve (V2) to the cavernous sinus suggested that the ION complex has the following four distinct segments: (1) ION and its terminal branches (5–11 branches) to the face distal to the infraorbital foramen, (2) ION within the infraorbital canal from the infraorbital foramen along the infraorbital groove (12 mm ± 3.2), (3) pterygopalatine segment within the pterygopalatine fossa which starts at the infraorbital groove to the foramen rotundum (13 mm ± 2.5), and (4) cavernous segment from foramen rotundum to the trigeminal ganglion (15 mm ± 4.1) which passes in the lateral wall of the cavernous sinus. Endoscopic anatomical landmarks and correlations were described for the infraorbital artery, maxillary artery, pterygopalatine ganglion, sphenopalatine nerve, greater palatine nerve, cavernous sinus, mandibular branch of the trigeminal nerve (V3), trochlear nerve, orbital floor, maxillary sinus, petrous and cavernous ICA, foramen rotundum, vidian nerve and vidian canal, eustachian tube, infratemporal fossa, lateral pterygoid muscle, and the pterygoid plates.

Conclusion: The ION is an easily identifiable and reliable landmark to foramen rotundum, cavernous sinus, pterygopalatine fossa, and anterolateral skull base during endoscopic transmaxillary approaches.