Microsurgical Anatomy Of The Keyhole Approaches

PartⅠ: Microsurgical anatomy of the supraorbital keyhole approach toupper basilar artery via the optico-carotid windowObjective: A quantitative anatomical study of the supraorbital keyhole approach to theupper basilar artery via the optico-carotid window was designed to explore its feasibilityand indication for upper basilar artery aneurysms. Our clinical experience was reported.Methods: After completing the supraorbital keyhole approach craniotomy on eightcadaveric heads, the width and length of the optico-carotid window and the length of thesupraclinoid internal carotid artery was measured. Measurement of the following wascarried out through the optico-carotid window:(1) linear distance (a) of the basilar arteryfrom the most proximal point of visualization of the basilar artery to the posterior clinoidprocess level (2) perpendicular distance (b) from the most distal point of visualizationalong the elongation of the basilar artery to the anterior fossa level. After posteriorclinoidectomy and orbitectomy, the measurement of (a) and (b) was repeated.Results: The width and length of optico-carotid window and the supraclinoid internalcarotid artery length were7.6±2.1mm,11.6±2.3mm, and12.7±2.4mm. The upper one-thirdof the basilar, bilateral superior cerebellar artery and posterior cerebral artery (P1segmentand part of the P2a segment) could be visualized through the optico-carotid window via thesupraorbital keyhole approach. The distance (a) was5.0±1.2mm, increased by3.4±1.0mmafter posterior clinoidectomy. The distance (b) was12.8±2.6mm, increased by3.3±1.2mmafter orbitectomy. Nine aneurysms were completely clipped without intaoperative rupture.All patients were discharged without neurogical deficits.Conclusion: For the supraorbital keyhole approach, the optico-carotid window is the mostideal window for upper BA aneurysms. When the width and length of the optico-carotid window are>5mm and>7mm, respectively, the supraorbital keyhole approach can meetthe requirement of exposure and manipulation of the upper basilar artery. The anteriorclinoidectomy can expand the window. The upper basilar artery aneurysms located <10mmhigher than the anterior fossa and not5mm lower than the posterior clinoid process can betreated via the supraorbital keyhole approach. Posterior clinoidectomy and orbitectomy canincrease the proximal and the distal exposure of basilar artery, respectively. PartⅡ: Microsurgical anatomy of the pterional keyhole approach to theinterpeduncular and prepontine cisternsObjective: An anatomical study of the pterional keyhole approach to the interpeduncularand prepontine cisterns was designed to study the extent of exposure, and compare thisapproach with the conventional approach quantitatively.Methods: A total of8(16sides) formalin-fixed cadaveric heads were perfused withcolored latex for this anatomical study. After completing the pterional keyhole approachcraniotomy, measurement of the following was carried out through the carotid-tentorialwindow:(1) the area of exposure (2) perpendicular distance from the most distal point ofvisualization along the elongation of the basilar artery to the anterior fossa level (3) lineardistance of the basilar artery from the most proximal point of visualization of the basilarartery to the posterior clinoid process level (4) the working angles of the basilar artery tip.Then a conventional craniotomy was performed, and the measurement was repeated forcomparison. At last, when the conventional bone flap was reconstructed and the posteriorclinoidectomy was performed via the keyhole approach, the measurement (3) wasrepeated.Results: In all16sides of the cadaveric specimens, the ventral aspect of the upper ponsand the lower mesencephalon, the upper one-third of the basilar artery, the bilateralsuperior cerebellar artery, the bilateral posterior cerebral artery (P1segment and part of theP2a segment), and the bilateral oculomotor nerve could be visualized through the carotid-tentorial window via the pterional keyhole approach. The exposure area and thelinear exposure of the basilar artery via the keyhole craniotomy had no significantlydifferent from that achieved with the conventional approach (P>0.05). The working anglesof the basilar artery tip were smaller for the pterional keyhole approach than for theconventional approach (P<0.0001). In the pterional keyhole approach, the perpendiculardistance from the most distal point of visualization along the elongation of the BA to theanterior fossa was13.5±2.6mm. The linear distance of the basilar artery from the mostproximal point of visualization of the basilar artery to the posterior clinoid process levelwas5.4±1.5mm. After posterior clinoidectomy, the distance increased significantly by5.1±1.0mm.Conclusion: Three surgical corridors (the carotid-tentorial window, the optico-carotidwindow and the posterior carotid bifurcation window) can be utilized to exposure theinterpeduncular and prepontine cisterns in the pterional keyhole approach. Thecarotid-tentorial window is the most ideal window for sufficient exposure, which hassimilar exposure compared with the conventional pterional approach, but the workingangles are smaller. The pterional keyhole approach is a minimally invasive surgicalprocedure for the treatment of the upper basilar aneurysm and the sellar tumor extended tothe retrosellar region. PartⅢ: Microsurgical anatomy of the occipital transtentorialkeyhole approachObjective: To design an occipital transtentorial keyhole approach based on the minimallyinvasive keyhole concept, study the extent of exposure, and compare this approach withthe conventional approach in terms of the area of exposure and the working angles. Toexplore the feasibility and surgical indication of the occipital transtentorial keyholeapproach and provide an anatomical basis for clinical applications.Methods: A total of8(16sides) formalin-fixed cadaveric heads were perfused with colored latex for this anatomical study. A longitudinal linear4-cm skin incision that beganat the upper margin of the transverse sinus,1.5cm away from the superior sagittal sinus,was designed for the occipital transtentorial keyhole approach. After the keyholecraniotomy was completed, the extent of exposure was examined. The area of exposure,the depth of the posterior third cerebral ventricle that could be observed and the workingangles were calculated using the neuro-navigation system. Then, a conventionalcraniotomy was performed, and the measurements were repeated for comparison.Results: The interhemispheric corridor and the supratentorial corridor can be utilized inthe occipital transtentorial keyhole approach. The surgical field extended superior to thesplenium, inferior to the superior medullary velum, ipsilateral to the middle and posteriorparts of the medial and inferior temporal lobe, contralateral to the pulvinar, and anterior tothe massa intermedia in the third ventricle. The exposure area of the occipital transtentorialkeyhole approach was72.05±6.26mm2and182.97±14.65mm2(P<0.0001) before and afterthe tentorial incision, respectively. The exposure area of the conventional craniotomy was187.28±20.16mm2, which was not significantly different from that achieved with theoccipital transtentorial keyhole approach (P>0.05). The horizontal and vertical workingangles of the five target points were all smaller for the occipital transtentorial keyholeapproach than for the conventional approach (P<0.0001). The depth of the posterior thirdventricle that can be observed was14.7±2.5mm via the occipital transtentorial keyholeapproach and15.1±2.4mm via the conventional approach (P>0.05).Conclusion: Compared with the conventional approach, the occipital transtentorialkeyhole approach is a more minimally invasive surgical procedure for treatment of thelesions in the pineal region and the middle and posterior parts of the medial and inferiortemporal lobe. However, the working angles are relatively narrow.