Microsurgical Anatomy Of The Presigmoid Transpetrosal Keyhole Approach

Part I: Design and Microsurgical Anatomy of the Presigmoid Retrolabyrinthine Keyhole ApproachObjective: To design a new presigmoid retrolabyrinthine keyhole approach based on minimally invasive keyhole idea and explore its feasibility and indications, which can be regarded as the bases of this approach in clinical use.Methods: Eight adult cadaveric heads fixed by formalin and perfused intracranial vessels by red and blue latex were used in this study. Based on the study of the skin incision of conventional presigmoid transpetrosal approach, a 7-cm postauricular C-shaped skin incision of presigmoid keyhole approach was designed and performed 1 cm behind the helix, with its upper border just above the pinna and inferior margin at the level of the intertragic notch. After stripping partial mastoid and temporal craniotomy, a 3.5cm×3cm bone window was performed. On ligating and dividing the superior petrosal sinus, retracting the cerebellar hemisphere and temporal lobe, many anatomic structures could be observed under microscope.Results: The important approach-relative structures could totally be exposed via the 7-cm postauricular C-shaped skin incision and the 3.5cm×3cm bone window. By means of adjusting head position and the angle of microscope, the ipsilateralⅢ,Ⅳ,Ⅴ,Ⅶ,Ⅷ,Ⅸ,Ⅹcranial nerves, posterior communicating artery, posterior cerebral artery, superior cerebellar artery, anterior inferior cerebellar artery, middle and superior segment of basilar artery, superior clivus, posterior cavernous sinus and the ventral lateral aspect of pons were exposed via this keyhole approach.Conclusion: The novel presigmoid retrolabyrinthine keyhole approach has practical value for clinical applications. With the techniques of modern microsurgery, several diseases such as petroclival meningeoma, small to medium acoustic neuroma without internal acoustic meatus invasion, tumor located at the ventrally lateral aspect of pons, aneurysm arising at middle or superior segment of basilar artery could be operated on via this presigmoid retrolabyrinthine keyhole approach without drilling the labyrinthine.Part II: Anatomical Study on the Presigmoid Translabyrinthine Keyhole Approach Assisted by NeuronavigationObjective: To design new presigmoid translabyrinthine keyhole approach assisted by neuro-navigation system according to the keyhole idea,and to explore the possibility of removing the approach-correlated bone precisely.Methods: Navigation data were established on 8 cadaveric heads fixed by formalin and perfused intracranial vessels with colored silicone. Before the operation, circumscriptions of sigmoid sinus, bony labyrinth and internal auditory canal were outlined with different colors in the navigation system in order to protect them in operation. A 7cm"C"shape skin incision was performed 1cm behind the helix with its super border near apex satyri and inferior margin at the level of intertragic notch. After elevating the skin flap and musculofascial flap respectively, a 3.5 cm×3 cm bone window was performed assisted by neuro-navigation. After skeletonized the sigmoid sinus, bony labyrinth and the canal for facial nerve, partial labyrinthectomy with petrous apicectomy and complete labyrinthectomy were performed by turns. The amount of dura exposed, the length of important structures exposed and the maximal angle of vision were measured in each step, and the anatomic structures were observed.Results: The incision of the presigmoid retrolabyrinthine keyhole approach fully met the needs of the presigmoid translabyrinthine keyhole approach. The bone overlying sigmoid sinus and bony labyrinth, the partial labyrinth and petrous apex, the whole labyrinth could precisely be drilled with the aid of neuro-navigation, which could avoid the bewilder in drilling process. This approach provided wide exposure to petroclival region, cerebellopontine angle, prepontine region and posterior cavernous sinus; an area between the III~XI cranial nerves was easily visible without significant brain retraction. Camparing with the retrolabyrinthine keyhole approach, both partial labyrinthectomy with petrous apicectomy and complete labyrinthecotomy can significantly increased the horizontal and vertical exposure, the length of some important structures and the maximal angle of vision (P<0.01), but there were no significant differences between partial labyrinthectomy with petrous apicectomy and complete labyrinthecotomy (P>0.05).Conclusion: The presigmoid translabyrinthine keyhole approach was feasible to be performed in our study. It provided easy and excellent exposure of the petroclival region and accorded to the keyhole idea. The approach correlated bone could be removed precisely assisted by neuronavigation system. The exposure was obviously increased by partial labyrinthectomy with petrous apicectomy or complete labyrinthecotomy, the former provided an excellent chance of hearing and facial nerve preservation..Part III: Quantification of the Presigmoid Transpetrosal Keyhole Approach to the Petroclival Region Assisted by NeuronavigationObjective: The goal of this study was to evaluate a new presigmoid transpetrosal keyhole approach based on quantitative measurements of the exposure of petroclival area assisted by Stryker neuronavigation system, which could be regarded as the bases of clinical application.Methods: The presigmoid transpetrosal keyhole approach was divided into four increasingly morbidity-producing steps: retrolabyrinthine keyhole approach (RLK), partial labyrinthectomy with petrous apicectomy keyhole approach (PLPAK), translabyrinthine keyhole approach (TLK) and transcochlear keyhole approach (TCK). Six latex-injected cadaveric heads (twelve sides) underwent dissection in which Stryker neuronavigation system was used. The area of petroclival exposure and surgical freedom with each subsequent dissection were calculated.Results: The exposed petroclival area of the four presigmoid transpetrosal keyhole approaches were(93.1±17.6)mm2(,340.1±47.1)mm2(,357.4±56.4)mm2 and(377.5±59.4)mm2, respectively. The exposed petroclival area of the PLPAK, TLK and TCK were all significantly increased than that of the RLK(P<0.01), but there were no significant differences between the PLPAK, TLK and TCK(P>0.05). The surgical freedom were (555.1±164.1)mm2,(714.1±203.8)mm2,(847.2±186.7)mm2 and(906.8±204.6)mm2, respectively. The surgical freedom of the PLPAK, TLK and TCK were all significantly increased than that of the RLK(P<0.01), and that of the TLK and TCK were all significantly increased than that of the PLPAK(P<0.01), but there were no significant differences between the TLK and TCK, the PLPAK and TLK(P>0.05).Conclusions: With each step, the surgical injury increased. The retrolabyrinthine keyhole approach spares hearing and facial function but has relatively limited utility. For lesions without bone invasion, the PLPAK provides a much more versatile exposure with an excellent chance of hearing and facial nerve preservation. The TLK provides for greater versatility in treating lesions but clival exposure is not greatly enhanced. The TCK adds little in terms of intradural exposure but should be reserved for cases in which access to the petrous carotid artery is necessary.