Endoscopic Anatomic Study In The Intradural Subtemporal Keyhole Modified Kawase Approach

Objective:This study aimed to observe the anatomical structures which can be exposed in the intradural subtemporal keyhole modified Kawase approach by using neuroendoscope and measure the distance between vital anatomical structures in this approach. We also discuss the indications and feasibility of the modified approach and provide anatomical basis for clinical application.Method:Simulated surgery via intradural subtemporal keyhole modified Kawase approach with assist from rigid neuroendo scope (4mm rod, from Rohtec, China) was performed on ten adult cadaver heads (Sixteen sides) fixed by formalin. A5cm vertical epifascial skin incision is created at the superior rim point of the zygomatic arch, which located1cm anterior to the tragus. The bone hole was2.5cm in diameter and the location shoud close to the cranial base. The lower edge of the bone hole should reach the skull base. The cerebral dura mater was opened through Semi-circular shape. The endoscope, through the subdural space, was used to observe the anatomic marks of the middle cranial fossa, including the cavernous sinus lateral wall, the space of tentorial notch and petroclival region. The surgical field was measured with comparing different milling range of petrous apex, and analysised the anatomical structure through this approach.Result:1. The important anatomic landmarks which have anatomic location in this approach, including tragus, zygomatic arch, arcuate eminence, trigeminal nerve, greater superficial petrosal nerve hiatus, greater superficial petrosal nerve (GSPN), petrous ridge, trochlear nerve, and oculomotor nerve. By using endoscope, the exposure range of this approach include cavernous sinus lateral wall, suprasellar region, incisure of tentorium of cerebellum, brainstem ventrolateral, and petroclival region.2. Measurement results:①The shortest distances from the zygomatic arch to foramen spinosum, foramen ovale, foramen rotundum, superior orbital fissure are29.35±0.64mm,33.04±1.25mm,45.95±2.20mm,20.62±1.13mm.②The shortest distances from the highest point of arcuate eminence to foramen spinosum, greater superficial petrosal nerve hiatus, the intersection of GSPN and mandibular nerve, the outside edge of the trigeminal impression are22.90±2.34mm、4.05±2.09mm、24.94±1.98mm、23.49±2.38mm.③Various anatomical triangles in the lateral wall of the cavernous sinus and the middle cranial fossa can be distinctly exposed, among which the Kawase triangle milling area is3.04±0.47cm2 and the area after the maximum milling of the petrous apex under the trigeminal impression is3.7±0.69cm2, the area increase0.66cm2.Conclusions:The intradural subtemporal keyhole modified Kawase approach can expose wide surgical area, including the middle cranial fossa, lateral wall of the cavernous sinus, suprasellar region, brainstem ventrolateral, incisure of tentorium of cerebellum, the middle and inferior petroclival region. Through the natural gap and grinding the petrous apex bone, it can be able to treat lesions in these areas. Compared with microscope, neuroendoscopic surgery has many advantages as following:minimally invasive, superior lighting, close observation, a wider field of view, the endoscopic probe is so slender that it can through a narrow gap to deal with deep lesions. It not only increases the security and accuracy of the operation, and also extend surgery indications to some extent.