Lateral Approaches To The Clival Region

Part I Microsurgical Anatomy of Clival Region: A Critical StudyObjective To study and review the microsurgical anatomy of the clival region that are directed through the lateral skull base.Materials and Methods Five adult cadaver heads fixed in formalin and 25 dry human skulls provided the materials for this study. The arteries and veins were perfused with colored silicone and examined under microscope with magnification. Dissections were performed to optimally expose and display the anatomic characteristics of the area while mimicking the actual surgical procedure. Special attention was given to the intrapetrous course of the internal carotid artery and facial nerve and their relationship to the structures in the temporal bone. Anatomic considerations is important for their management during surgery are reviewed. In the final steps of the dissections, the cerebral and cerebellar hemispheres were removed and the venous sinuses in the dura matter lining the clival region were reviewed. Surgically important landmarks and bony relationships were reviewed and measurements were obtained.Results From a surgical standpoint the intradural compartments of the clival region could be divided into three different spaces: (1) an inferior space related to the medulla and to the structures around the region of the foramen magnum;(2) a middle space related to the pons and to the structures in the prepontine and cerebellopontine cisterns; (3) a superior space related to the contents of the interpeduncular cistern, and to the sellar and parasellar regions. The extradural portion of the clival region is related to the structures inside the petrous temporal bone and infratemporal fossa and the major venous sinuses draining the area. The most important anatomic details were directed to the course of the facial nerve and internal carotid artery in the temporal bone and major venous pathways draining the region.Conclusions Pathologic process arising at the clival region present difficult surgical problems because of their closed relationship to the brain stem, multiple cranial nerves, and to the major vessels in the posterior circulation. The clinical presentation, as well as the selection of the best surgical approach, depends on the location, extension, size, and nature of the pathology. Lesions can arise anywhere within the clival region and frequently are not restricted to a single anatomic compartment of the skull base. Involvement of multiple cranial nerves and arteries occurs because skull base tumors tends to achieve considerable size before producing clinical manifestation. The distinction between the benign or malignant tumors in this areas is not rigid as many benign tumors can have very invasive characteristic. Detailed understanding of the regional anatomic information and pathological anatomic variations will play a critical role in dealing with the clival lesions. Part II Modified Orbitozygomatic Approach: A Practical Anatomical StudyObjective To compare the technical results between traditional orbitozygomatic (OZ) approach and modified OZ approach through cadaver dissection and operative simultation.Method We use the so-called "two-flaps" technique for the modified OZ approach. performed on three cadaveric heads. Initially a frontotemporal bone flap is turned, followed by the "six bone cuts" with pneumatic saw to divide the root of zygomatic process, malar eminence, lateral orbital rim, lateral orbital wall, superior orbital rim as well as the orbital roof. After the orbitozygomatic bone flap is freed, the intradural microsurgery will be proceeded.Results Compared with pterional approach, we found both of the modified and traditional OZ approach could provided resemble significantly decreased operating distance,as well as the widened viewing-angle when handing the deep seated lesions, this has reduced the difficulty of microsurgical operation at skull base and brain retraction. The modified OZ approach eliminates the bone lose during operation, and the need for bone reconstruction of the orbital walls to prevent the postoperative complication of enophthalmos. It also minimizes the risk of injury to the frontal branch of the facial nerve and the damage to the eyeball. Once the serious infection related to the bone flap after procedure, this "two-flap" technique will show its practical superiority.Conclusion Generally the modified OZ approach could avoid iatrogenic cosmetic problems and decrease the possibilities of eyeball damage after procedure. Part III Modified anterior transpetrosal Approach: Anatomical StudyObjective To compare the technical results between traditional Kawase approach and modified anterior transpetrosal approach, through cadaver dissection and operative simultation.Methods Operation simultation was performed on 3 cadaveric heads. A free anterior and middle temporal craniotomy is created to the base of the middle fossa, followed by drilling and flattening the superior surface of the zygomatic arch. The dura is elevated from the floor of the middle fossa to expose the Kawase's triangle. After the petrosal apex is drilled away, the tentorium is cut and extended with "T" shaped fashion by intradural and subtemporal exposure.Results Compare with the traditional Kawase approach, the modified anterior transpetrosal approach was placed more anteriorly and was combined with removal of the superior part of the zygomatic arch, provided widened visulization to the area of the upper one-half clivus and the ventral surface of the mesencephalon and upper pons. Meanwhile decrease the retraction on temporal lobe in avoiding of the damage to the vein of Labbe.Conclusion The modified anterior transpetrosal approach more greatly facilitates access to the upper one-half clivus and the ventral surface of the mesencephalon and upper pons. Part IV Microsurgical Resection of Petroclival Meningiomas by Modified Suboccipital Retrosigmoid ApproachObjective QTo introduce the operative experience and methods in microsurgical resection of large petroclival meningiomas by modified suboccipital retrosigmoid approach.Methods After the suboccipital retrosigmoid craniotomy completed, care must be taken to skeletonize the lateral and sigmoid sinuses, and the incised dura is fully drawn upward and sideways. We then proceed to debulk the tumor throughout the fissure of nerves, followed by detaching the lesion in succession from the cranial nerves and the brain stem, and subsequently the tumor is removed in piecemeal manner. If the tumor extend into the middle fossa, we are able to resect it upward after incising the tentorium. If the tumor involves the low clivus and foramen magnum, it could be removed by the combined retrosigmoid and far lateral approach. For those tumor invading the cavenous sinus and brain stem with obvious infiltrative pattern on MRI, radical resection is not attempted whereas the brain stem decompression is the goal of the surgery.Results Total removal was achieved in 9 cases (60%), and the immediate postoperative new cranial nerve deficits occurred in 6 cases (40%). Good recovery was obtained in 13 cases (86.7%) with 6-months follow-up.Conclusion Even by the simple suboccipital retrosigmoid approach, which combined with some novel technical modifications, the large petroclival meningiomas could be surgically treated with good clinical results. PartV The quantitative and anatomical comparison between pterional and orbitozygomatic approach to the upper clival lesionsObjective To provide scientific basis for the selection of operative approach when treating the upper clival lesions through the quantitative comparison in surgical exposure and working angle between pterional and orbitozygomatic approach.Methods The pterional and orbitozygomatic approaches were performed on seven cadaveric heads (fourteen sides), the surgical exposure and working angle of two approaches which targeting the upper clival region, were measured and calculated respectively with the neuro-navigation system, and followed by statistically analysis.Results The working angle was significantly greater with the orbitozygomatic approach than that with the pterional approach (p < 0.05 ) . Moreover, the orbitozygomatic approach also provided a wider operative exposure than the pterional approach, but there was no significant difference between them.Conclusion Compared with pterional approach the orbitozygomatic approach could provide wider surgical exposure, as well as significantly increased working angle when dealing with the upper clival lesions. Consequently, the orbitozygomatic approach would improve the surgical maneuverability and reduce the brain retraction during operation. Part VI The quantitative comparison of the exposure to petroclival region by different transpetrosal approachesObject. To provide scientific basis for the selection of surgical approach, the quantitative comparision of the exposure to petroclival region by different transpetrosal approaches was performed.Methods: The retrolabyrinthine, translabyrinthine, and transcochlear approaches were performed in succession on 7 latex-injected cadaveric heads (fourteen sides), in which neuronavigation was used to quantify and compare the areas of exposure to petroclival region by different approaches, meanwhile to observe the correlated morbidity of cranial nerves caused by these approaches.Results: The retrolabyrinthine approach spares hearing and facial function but provides for only a smaller exposure. This is significantly less than with the translabyrinthine and transcochlear approaches (p < 0.05) . Moreover there is no significant difference between the later two approaches, both of them may lead to deafness and dysfunction of facial nerve.Conclusion: The transpetrosal approach can offer excellent exposure to the petroclival region but should be used judiciously due to the high level of morbidity of surrounding injury. For patients without hearing preoperatively, the translabyrinthine approach is optimal option fot its greater exposure. The transcochlear approach is too invasive to be used as a routine. The retrolabyrinthine approach is the best option for patients with hearing. Part VII Occipital Condyle: morphometric classcification and surgical significance for the lesions of lower clivusObjective The classification protocol of occipital condyle (OC) was established based on the morphometric measurements and analysis for the OC and foramen magnum (FM),, to provide scientific basis in determining whether or not partially remove the OC, for the lesions of lower clivus by suboccipital-lateral approach.Methods The correlated anatomical structures were measured and evaluated in 100 dry adult skulls and 20 measurements obtained from three-dimensional computed tomography (3D-CT), including the length of FM (FML), the width of FM (FMW), anterior-posterior distance of OC (AOCP) and Axis of OC (OCA) .The OC classification index (OC index) was defined as the ratio of AOCP/FML. After morphological classification for 100 skull specimens, the viewing angle of pre and post-drilling of posterior 1/3 condyle were statistically compared in each group.Result In cadaveric study the mean distance of FML,FMW,AOCP and OCA were 34.81±2. 24mm,29.11±2. 24mm,15.99±1. 66mm,23.92±2. 44mm respectively. Accordingly on 3D-CT measurements their mean data were 34.79±1.77mm,29.19±2. 24mm,16.05±1. 68mm,24.78±2. 39mm. Based on the OC index, the 100 skulls were classified into Type I(small condyle, 8%),type II(middle condyle, 74%) and type III(large condyle, 18%). There was no statistical difference between the pre and post-drilling viewing angle in type I group (p > 0.05) ,but statistical difference was demonstrated in type II (p < 0.05) and particularly significant in type III group (p<0.01) .Conclusion Great morphometric variations were found in occipital condyle. Identifying the type of condyle using preoperative 3D CT scans, was indispensable for the surgical planning in dealing with the lesions of lower clivus.