Endoscopic Anatomic Study Of The Neuronavigational Assisted Intradural Subtemporal Keyhole Approach

Objective The purposes of this study were to evaluate the feasibility and the advantages of a purely endoscopic intradural subtemporal keyhole approach(EISKA)to the petroclival and ventrolateral brainstem regions,and to assess the value of neuronavigational assistance in the EISKA.Moreover,the advantages of endoscopy in these approaches were also evaluated by studying anatomic exposure and surgical freedom in the posterior cranial fossa.The final purposes were to provide anatomic and theoretical basis for the clinical transformation of the EISKA and to provide new methods for the treatment of the lesions in the petroclival and ventrolateral brainstem regions.Methods 1.Twenty EISKAs were performed on 10 cadaveric heads and the vertical distances of the natural intracephalic interspaces in the suprasellar region were recorded.2.An intradural Kawase approach and a navigation-assisted intradural Kawase approach were then carried out on a random side of each specimen.Two types of the milled Day rhombus ranges and the thicknesses of the residual bones were compared.3.Related anatomic structures were observed through an endoscope and a microscope at the end of each approach.Anatomic exposure and surgical freedom were measured by transparent graph paper and be analyzed.Results 1.This keyhole endoscopic technique clearly visualized the anatomic structures in the suprasellar,petroclival and ventrolateral brainstem regions via an intradural subtemporal route.Most of the structures in the suprasellar region could be observed by oculomotor nerve-posterior communicating artery space.The vertical distance between internal carotid artery(C6)and oculomotor nerve was 8.21±0.90mm,between posterior communicating artery and tentorium was 8.32±1.64 mm on average.2.Using a frameless navigational device,the mean area of the milled Day rhombus was larger than which in the intradural Kawase approach(276.8±14.6 mm~2 vs.244.8±12.6 mm~2,P<0.05),and the thicknesses of the residual bones including the superior wall of internal acoustic meatus(1.0±0.2 mm vs.2.5±0.4 mm),the medial superior wall of cochlear(1.0±0.2 mm vs.3.0±0.4 mm)and the superior wall of petrous segment of internal carotid artery(1.2±0.2 mm vs.3.4±0.4 mm)were all thinner than which in the intradural Kawase approach(all P<0.05).3.Compared with microsurgical,the superior,inferior and medial limit of the endoscopic anatomic exposure increased by 2.9,15.65 and 10.2 mm while the surgical freedom increased by 2.9,7.55 and 6 mm(P<0.05)in the intradural subtemporal keyhole approach;in the intradural Kawase approach,the anatomic exposure increased by 2.7,20 and 29.5mm while the surgical freedom increased by 2.7,14.8 and 8.8 mm(P<0.05);and in the navigation-assisted intradural Kawase approach,the anatomic exposure increased by 3.1,20.3 and 29.9 mm while the surgical freedom increased by 3.1,15.3 and 8.8mm(P<0.05).Using a frameless navigational device,the inferior limit of the anatomic exposure increased 3.8 mm by endoscopy and 3.5 mm by microscopy while the surgical freedom increased by 2.7 mm and 2.2,respectively(P<0.05).Conclusions 1.The EISKA can facilitate ideal observation of the petroclival and ventrolateral brainstem regions with less invasiveness.2.The oculomotor nerve-posterior communicating artery space has the high availability in the EISKA to the suprasellar region.3.More anatomic exposure and surgical freedom can be achieved via neuronavigational assistance with fewer complications.4.Compared with the microscopy in these approaches,the endoscopy can provide more anatomic exposure and surgical freedom mainly in the superior,inferior and medial directions of the brainstem regions.5.The EISKA and intradural Kawase approach are considered a valuable technique for the removal of lesions located on the suprasellar,petroclival and ventrolateral brainstem regions with less invasiveness and fewer complications.