Microsurgical endoscopic-assisted retrosigmoid intradural suprameatal approach : anatomical considerations

AIM: The aim of this study was to evaluate the feasibility of microscopic endoscopic assisted suprameatal tubercle drilling with a retrosigmoid approach and it focuses on the anatomic structures identified with the endoscope. The advantages of the 30 degrees optic view are also described. METHODS: Fifty dry temporal bones were studied in order to estimate the variability of the prominence of the suprameatal tubercle. Eight fresh cadaveric specimens were prepared for a retrosigmoid approach to allow for microscopic endoscopic assisted suprameatal tubercle drilling. The increase in trigeminal exposure and neurovascular structures visualization with the endoscope, using 0 degrees and 30 degrees optics were then evaluated. RESULTS: Three major types of the suprameatal tubercle were found: 1) a large size tubercle (> 6 mm, 9/50 cases); 2) a medium size tubercle (3-6 mm, 37/50 cases); and 3) an almost absent suprameatal tubercle (< 3 mm, 4/50 cases). Microscopic endoscopic assisted suprameatal tubercle drilling with opening of the Meckel's Cave was found to be technically feasible in all cases. The increase in trigeminal nerve exposition was of 9 mm on average. Endoscopic exploration with 0 degrees and 30 degrees optics made possible the identification of all neurovascular structures in the area. CONCLUSION: Microscopic endoscopic assisted suprameatal tubercle drilling is a feasible procedure that allows the identification of all neurovascular structures in the cerebellopontine angle and petrous apex region. The opening of Meckel's Cave may be particularly useful for lesions located in the cerebellopontine angle having a minor component that extends anteriorly and laterally in the middle cranial fossa