Anatomical Study Of Lateral Skull-base Approaches To Petroclival Region

Objective Surgical access to lesions of petroclival region represents a challenge , both because of the depth of the lesion site and the vicinity of complex neurovascular structures. Maximal exposure of the lesion with minimal approach-related complication is the most important problem to deal with in the microsurgery of these lesions. For this, accurate knowledge of the surgical anatomy of this region is mandatory, and the choice of type of approach is based on the location of lesion, preoperative neurological deficit, and extent of tumor removal in preoperative planning, etc. Surgical approach to petroclival region can be classified into anterior and lateral approach, the latter is widely used today. In order to understand the detailed anatomy of petroclival region and master the exquisite microsurgical skills in lateral approach, three representative skull-base approach and relative anatomy were studied.Methods Twenty formalin-fixed human adult cadaveric head (40 sides) were examined. Arteries were injected with red silicone in all heads and veins injected with blue silicone in 7. The definition of petroclival region used in this study is as follows: The petroclival region is the area between dorsum sellae and anterior border of foramen magenum which is medial to, anterosuperiorly to posteroinferiorly, the Meckel's cave, internal auditory foramen, jugular tubercle, and occipital condylar. The approaches studied were subtemporal transtentorial anteiror transpetrosal approach, suboccipital extreme lateral transcondylar approach, and presigmoid transpetrosal approach. 10 heads (20 sides) were used in each approach, the former two approach were studied in the same 10 heads, and the petroclival structures are measured and filmed. The data was statistically analyzed. My personal experience in dissection was summarized.Results (1) In subtemporal transtentorial anterior transpetrosal approach, the zygomatic arch should be removed to minimize the temperal lobe retraction. Therhomboid area of Kawase is bordered anteromedially by posterior border of trigeminal nerve, posteromedially by petrous ridge, posterolaterally by arcuate prominence (AP), anterolaterally by great superficial petrosal nerve (GSPN). The internal auditory canal is corresponding to the bisectrix of triangle formed by AP and GSPN. A line through the internal auditory foramen that is perpendicular to the GSPN and the internal auditory canal divided the rhomboid Kawase area into three triangle. Except for the internal carotid artery in its lateral border, there is no important structure in the anterior triangle which is the main area to drill the petrous apex. The cochlea is located in the depth of middle triangle. Whether the bone in the posterior triangle should be drilled depend on fact whether the internal auditory canal is involved. After pectrosectomy, the size of the windows in the superior and medial surfaces of petrous bone averaged 2.6cm2 and 1.9cm2, respectively. The exposure of this approach include cavernous sinus, Meckel's cave, the upper petroclival region and ventral surface of brain stem above the level of internal auditory canal. (2) The presigmoid transpetrosal approach have four subtypes including retrolabyrinth, partial labyrinthectomy, translabyrinth, transcochlear approaches. During the craniotomy, the anion can not precisely predict the junction of transverse-sigmoid sinus. The most superior mastoid point, temporal line, and mastoid tip can be used to locate the sigmoid sinus. Except for the well-known vein of Labbe, the bridging vein of basal temporal and occipital lobe vary and need to be protected as much as possible. The structures in petrous bone including inner ear structures, facial nerve, jugular glomus have a complex anatomical relationship, so that they should be adequately exposed as needed in different subtypes of presigmoid approach. The basic subtype of presigmoid transpetrosal approach has a limited exposure which can not truly expose the inner surface of petrous apex and middle clivus. The partial labyrint...