Microscopic and Endoscopic Anatomy of the Foramen Magnum and Cranio-vertebral Junction in a Transtubular Far Lateral Approach

Introduction: The far lateral approach is commonly used in neurosurgical practice for the removal of lesions localized at the the cranio-vertebral junction (CCJ). We propose a novel minimally invasive far lateral approach performed through a tubular retractor. The anatomy, as seen through the tubular retractor, takes on a different perspective when compared to the standard anatomical view provided by the surgical microscope, and needs to be studied in detail in order to achieve familiarization with this different surgical perspective. We evaluate the anatomic areas of the cranial base exposed by a microscopic and/or endoscopic transtubular far lateral approach.

Methods: A minimally invasive far lateral approach was performed through a tubular retractor system on 6 preserved cadaveric heads (12 sides) injected with colored latex. A ViewSite™ Brain Access System (Vycor Medical, Inc.) of tubular retractors was used. On six sides a partial condylectomy was performed, and on the remaining six sides the approach was completed with resection of the jugular tubercle.

Results: We divided the foramen magnum and cerebellopontine regions into lateral, middle, and medial compartments. The anterior-medial compartments towards the midline were difficult to explore using the microscope alone and required the aid of the endoscope. The tubular retractor provided general circumferential visualization of the anatomical structures, particularly the structures localized in the more lateral compartments. Use of the endoscope allowed for better perception of the depth of the field as compared to the microscope. Our study also identified optimal and safe surgical corridors for insertion of the tubular retractor.

Conclusions: A transtubular far lateral approach completed with a partial extradural resection of the condyle provides excellent exposure of the cranio-vertebral junction. Use of the endoscope allows for better visualization of the surgical compartments towards the midline and for better in-depth surgical exploration of each intradural compartment.