Microsurgical Anatomy Studies On Keyhole Approach In The Midline Region Of Brain

Part I: Microsurgical Anatomic Study on the Transcallosal Lateral Ventricle Keyhole Approach Objective: The feasibility study of transcallosal lateral ventricle keyhole approaches would be done. The scope of operation exposure of transcallosal lateral ventricle keyhole approach was to be studied, as so the roles of anatomic factors correlated to the operation exposure. Subsequently, the design principles and methods of the keyhole approaches would be investigated. Methods: Transcallosal ventricle keyhole approaches were put into practice in 16 normal Chinese adult cadaveric heads, which arteries and veins were perfused with colored latex, assisted by neuronavigation. The exposure scope of the keyhole approaches was studied. The data of anatomic structures correlated to the keyhole approaches were measured with Stryker navigation system and analyzed by the sagittal operation angle and coronal operation angle with SPSS 10.0. Finally, according to these analytical results, the transcallosal ventricle keyhole approaches were designed and applied in cadaveric heads. Results: The operations of the transcallosal lateral ventricle keyhole approaches were accomplished in the cadaveric heads accurately assisted by Stryker neuronavigation. The main anatomic factors correlated to sagittal operation angle are the length of bone window(r=0.462), length of opening of corpus callosum(r=-0.185), the distance between bone window and opening of corpus callosum(r=-0.300), ipsilateral/contralateral bone window(r=0.206), positional angle of opening of corpus callosum(r=-0.119), positional angle between the bone window and opening of corpus callosum(r=0.263). All that the length of opening of corpus callosum(r=0.158), the distance between bone window and opening of corpus callosum ( r=0.523 ) , ipsilateral/contralateral bone window(r=0.162), positional angle of opening of corpus callosum(r=-0.197), positional angle between the bone window and opening of corpus callosum(r=-0.175) are correlated to coronal operation angle. The two regression equations of sagittal and coronal operation angle were obtained from processing the data. The frontal horn could be exposed with A-Ⅰ,M-Ⅱ,M-Ⅰ,P-Ⅱand P-Ⅰkeyhole approaches. With A-Ⅰand M-Ⅱapproaches the posterior part of frontal horn could be expoxed.The top part of frontal horn could be exposed with P-Ⅱand P-Ⅰkeyhole approaches. The whole body of lateral ventricle could be exposed with A-Ⅱ,M-Ⅱ,M-Ⅲand P-Ⅲkeyhole approaches. The anterior half of the body could be exposed with A-Ⅰand P-Ⅱapproaches, but A-Ⅲapproach to the posterior half. The atrium of lateral ventricle could be exposed with A-Ⅱ, A-Ⅲ, M-Ⅲand P-Ⅲkeyhole approaches, among them P-Ⅲapproach only to anterior-medial part of atrium, A-Ⅱand M-Ⅲapproaches to the medial part and A-Ⅲapproaches to the occipital horn of lateral ventricle. Conclusions: The sagittal and coronal operation angles are the excellent scales to objectively assess the exposure scope of transcallosal lateral ventricle keyhole approaches. The exposedness of the keyhole approaches is regulated by the harmony force of many interrelated factors. Regression equations of sagittal and coronal operation angles could help neurosurgeons to grasp all the most important anatomic factors correlated to the exposure of the keyhole approaches. The transcallosal lateral ventricle keyhole approaches are satisfactory of exposure in the frontal horn, body, atrium and occipital horn of lateral ventricle. PART II: Anatomic Study on the Transcallosal Third Ventricle Keyhole Approach Objective: The microsurgical anatomy of transcallosal third ventricle keyhole approaches was to study. The feasibility and differences studies of transcallosal interforniceal, transchoroidal and transforaminal keyhole approaches were to done. Methods: The designs of transcallosal interforniceal keyhole approaches,transchoroidal keyhole approaches and transforaminal keyhole approaches were accomplished with Stryker neuronavigation system. All the designed keyhole approaches were performed in the 16 normal Chinese adult cadaveric heads. The anatomic structures, such as lateral ventricle, foramen of Monro, choroid fissure, fornix, third ventricle and so on, were investigated. The data of anatomic structures obtained by measuring with Stryker navigation system. Results: The transcallosal interforniceal, transchoroidal and transforaminal keyhole approaches were accomplished successfully assisted by neuronavigation in cadaveric heads. The exposednesss in not only third ventricle after foramen of Monro but also middle part of pineal region through velum interpositum could be obtained with the transcallosal interforniceal anterior keyhole approach and middle keyhole approach. Almost the whole third ventricle would be exposed with transcallosal interforniceal posterior keyhole approach, but the anterior-upon part of third ventricle before foramen of Monro. The exposure scope in the third ventricle with A-Ⅲ, A-Ⅱ, M-Ⅲ, A-Ⅰ, M-Ⅱ, P-Ⅲand P-Ⅱtranschoroidal keyhole approaches were antedisplacement gradually from the habenular commissure to tuber cinereum. The ipsilateral half of pineal region could be exposed through the choroids fissure in the atrium with A-Ⅱ, A-Ⅲand M-Ⅲtranschoroidal keyhole approach. The exposure scope in third ventricle with the transforaminal third ventricle keyhole approaches was small under normal anatomy condition, and the exposure locus was regulated by the position of bone window. The exposure scope would be increased, as foramen of Monro be amplified by cutting off the column of fornix. Conclusions: The transcallosal interforniceal, transchoroidal and transforaminal keyhole approaches to the third ventricle could be performed successfully in cadaveric heads. The exposure scope of the transcallosal interforniceal third ventricle keyhole approach is more than it of the transchoroidal approach. The ipsilateral half of pineal region could be exposed with A-Ⅱ, A-Ⅲand M-Ⅲtranschoroidal keyhole approaches. The middle part of pineal region could be oxposed with the transcallosal interforniceal anterior and middle keyhole approaches. Trasforaminal keyhole approaches to the third ventricle are good assistant approaches, though its exposurescope is less than the other approaches'. PART III: Microsurgical Anatomic Study on the Infratentorial Supracerebellar Keyhole Approach Objective: The feasibility study of the infratentorial supracerebellar keyhole approach was to be done. The microanatomy and applied strategies of the keyhole approach would be studied. All these studies were to found the theory foundation for the applications of the keyhole approach to pineal region. Methods: The infratentorial supracerebellar keyhole approach was performed in the 16 normal Chinese cadaveric heads, after perfusion of the arteries and veins with colored latex, assisted with neuronavigation. The anatomy structures, such as cerebellum, tentorium of cerebellum, vein of Galen and its tributaries, pineal body, velum interpositum, corpora quadrigemina, and medial posterior choroidal artery and so on, were studied ,using a magnification ranging from 3 times to 25 times. The data of anatomic structures, obtained by measuring with Stryker neuronavigation in live operation, were analyzed in correlation to the keyhole operation. Results: The operation of infratentorial supracerebellar keyhole approach could be accomplished successfully in cadaveric heads accurately assisted by neuronavigation. The keyhole bone window with (20㎜-25㎜)×(25㎜-30㎜)could be obtained by the mill in the keyhole approach operation. Except the cermian bridging veins, no other vessel need to be sacrificed in the operation of infratentorial supracerebellar keyhole approach. After the Galen veins curtain, which is a characteristic structure caped with arachnoid in pineal region, was dissected, Galen vein and its tributary could be exposed entirely in security.. Pineal body and its above structures under tentorium of cerebellum could be exposed by retraction of cerebellum culmen. The whole quadrigeminum and adjacent structures, even trochlear nerve, could be viewed by retraction of wing of central lobule of cerebellum in the paramedian. The third ventricle could be gotten into with less damnification by opening the inferior membrane of the tela choroidea mediallyto posterior medial choroidal artery under ipsilateral internal cerebral vein. The area of operation region was increased to longitudinal dehiscence region by splitting the tentorium of cerebellum between straight sinus and lateral sinus. Conclusions: The operation of infratentorial supracerebellar keyhole approach could be accomplished successfully assisted by neuronavigation. There are no other blood vessels damaged except vermian group bridging veins in the keyhole operation. The Galen veins curtain could be dissected in security. All the anatomic structures in pineal region could be exposed with the infratentorial supracerebellar keyhole approach, and with it the third ventricle can be gotten into with almost no damage. The infratentorial supracerebellar keyhole approach is a mini-invasive approach to be considered for treatment of lesions involving the pineal region.