Visualization of Dark Side of Skull Base with Surgical Navigation and Endoscopic Assistance: Extended Petrous Rhomboid and Rhomboid with Maxillary Nerve–Mandibular Nerve Vidian Corridor

Background

Lesions located at the petrous apex, cavernous sinus, clivus, medial aspect of the jugular foramen, or condylar regions are still difficult to fully expose using the operating microscope. Although approaches to this region through the middle cranial fossa have been previously described, these approaches afford only limited visualization. We have confirmed a transcranial infratemporal fossa combined microsurgical and endoscopic access to the petrous apex, clivus, medial aspect of the jugular foramen, and occipital condyle. We have presented the results of a micro-anatomical cadaver dissection study and its clinical application.

Methods

Ten latex-injected cadaveric specimens (20 twenty sides) underwent dissection with navigational guidance to achieve an extended anterior petrosal approach combined with a far vidian corridor approach (between the foramen rotundum and foramen ovale). We performed anatomical dissections to confirm the surgical anatomy and the feasibility and limitations of this approach. Anatomical dissections were performed in the skull base laboratory of Lariboisière Hospital and Duke University Medical Center. This approach was then applied to some clinical cases.

Results

The combination of the microscope and endoscope, aided by surgical navigation, was extremely effective and provided a wide view of the petrous rhomboid, the entire clivus, and the medial condylar regions. The extended extradural anterior petrosal approach provided a large corridor to petrous and clival lesions. Endoscopic assistance allows for wide and deep exposure of the middle to lower clivus, epipharyngeal space, and bilateral condylar regions. This approach successfully provided adequate surgical access for resection of tumors located in these regions. The depth of the medial aspect of the jugular foramen was 16.3 ± 1.2 mm deep from the geniculate ganglion. The emerging point of the inferior petrosal sinus in the jugular foramen was 16.5 ± 1.8 mm deep from the geniculate ganglion. The hypoglossal canal was 21.6 ± 2.2 mm deep from the geniculate ganglion. The foramen magnum was located 31.5 ± 2.4 mm deep from the gasserian ganglion. The inferior petrosal sinus was found to be a reliable landmark to identify the medial portion of the jugular bulb. The introduction of the endoscope through the middle fossa rhomboid enabled visualization of the medial aspect of the jugular bulb, which otherwise would be hampered by the internal auditory canal under the microscope.

Conclusion

After microscopic exposure of the middle fossa rhomboid, neuronavigational endoscopic assistance facilitated visualization of the ventral cavernous region, petrous apex, retropharyngeal space, and middle and inferior clivus down to the medial aspect of the jugular bulb and condyle regions. Additional maxillary nerve–mandibular nerve vidian corridor visualization provides a lateral transsphenoidal approach to upper clivus lesions.

Introduction

During the previous 30 years, skull base surgeons have developed extended skull base techniques to access difficult anatomic areas.¹ Even with these techniques, and with advanced microscopic visualization, some areas of the skull base, such as the ventral cavernous sinus, petrous apex, clivus, and the medial aspect of the jugular bulb and condylar regions, have remained hidden to the microscope. Recently, transnasal approaches through the sphenoid and maxillary sinuses and transpterygoid and/or transclivus approaches have been used successfully to treat medial jugular lesions and lower clivus condylar lesions. Despite these developments, we have sometimes still realized a benefit from the use of transcranial approaches because these do not share some of the limitations of even extended endoscopic exposures (e.g., lesions that extend above and below the lateral cavernous sinus).

During the past 5 years, our group has been aiming to visualize these hidden areas using high-resolution 4-mm, rigid endoscopic techniques with transcranial approaches. We have found a unique benefit in anatomical visualization by combining these techniques with our previously described extended skull base approaches. In the present report, we have described a navigational endoscopic study using cadaveric head specimens and clinical applications, focusing on the extended anterior petrosal approach.

The purpose of the present study was to perform a morphometric analysis of the extended middle fossa rhomboid and an additional maxillary nerve (V2)-mandibular nerve (V3) vidian corridor to the middle and lower clivus around the medial jugular bulb and condyle using cadaveric head models (Figures 1 and 2) and to report our clinical experience with these approaches.