Endoscopic Intradural Subtemporal Keyhole Kawase Approach to the Petroclival and Ventrolateral Brainstem Regions

Objective: To study the endoscope anatomy of the petroclival and ventrolateral brainstem regions via the intradural subtemporal keyhole Kawase approach and discuss the feasibility and indications of this approach to the regions. Materials and Methods: Craniotomy procedures performed via the intradural subtemporal keyhole Kawase approach were simulated on 16 sides of 8 adult cadaveric heads fixed by formalin, and the related anatomical structures were observed through the 0-degree endoscope or alternatively 30-degree one. Measurements of the shortest distances from the highest point of arcuate eminence to the 4 anatomic marks and the lengths of the Kawase rhombus were recorded, and the 2 kinds of milled ranges of petrous apex were compared. Result: Most of the related anatomical structures could be clearly observed under the endoscope. The shortest distances from the highest point of arcuate eminence to the foramen spinosum, the greater superficial petrosal nerve hiatus, the intersection of the greater superficial petrosal nerve and mandibular nerve, and the outside edge of the trigeminal impression are 22.90 +/- 2.34, 14.05 +/- 2.09, 24.94 +/- 1.98, 23.49 +/- 2.38 mm. The area of routine milled Kawase rhombus is 3.04 +/- 0.47 cm(2), which would increase 0.66 cm(2) on average after the maximum drilling of the petrous apex. Conclusions: The intradural subtemporal keyhole Kawase approach can provide an ideal exposure to the petroclival and ventrolateral brainstem regions via the endoscope with less damaging of the normal structures. It can be used to treat the lesions located in those areas through the natural gap combined with the drilling of petrous apex bone.