| Background:Due to deep location and narrow surgical corridor surrounded by vital neurovascular structures,including the hypothalamus near the anterior part of the floor,the midbrain below the floor,thalamus beside the both lateral walls of the third ventricle;fornix,internal cerebral vein and thalamostriate vein on the roof;optic chiasm and anterior cerebral complex near the anterior wall;pineal body beside the posterior wall of the third ventricle,approaching the third ventricle for tumor resection is a veritable challenge for neurosurgeons.With the rapid development of neuroendoscopic techniques and tools,transcranial endoscopic keyhole surgery has gained great progress.And neuroendoscopy have some advantages(close observation and panoramic view)access to the third ventricle via various approaches over microsurgery.The quantitative anatomic study of comprehensively endoscopic approaches to the third ventricle is scarce at present.The objective of the study is to quantitatively assess and compare the exposure and microsurgical maneuverability of three absolutely endoscopic keyhole approaches,including interhemispheric transcallosal transchoroidal(TCTC),frontal transforminal transchoroidal(TFTC)and supraorbital subfrontal translamina terminalis(SFTLT)approaches.The study could provide some anatomic evidence for neurosurgeons’the most suitable approach selection for dealing with the various third ventricle lesions,which may be beneficial for the patients and promote decreasing disability rate and fatality rate.Methods:Anatomical dissections and exposure of the important structures of the third ventricle were performed using six formalin-fixed(Formalin was only injected into arteries)and color latex-injected cadaveric human heads(twelve sides,Male:Female=4:2;Mean age:72.3 years)under 0°or 30°rigid endoscope.Compared with fresh cadaveric heads,these heads,whose arteries were injected with formalin,had more stable ventricular and cerebral structures;Meanwhile,different from the hard brain tissue of cadaveric heads completely immersed in formalin,the brain tissue of these heads were relatively soft,which could facilitate the dissection of anatomical fissure.The working channel was created through the natural fissure of brain tissue or traction of flat retractors in the TCTC and SFTLT approach.Notably,in order to maximum reduce the injury of cerebral cortex and white matter,tubular retractor system was used to create the working channel between the frontal lobe and the third ventricle in the TFTC approach.Compared with the flat retractors,tubular retractor system can reduce the risk of parenchymal disruption and minimize the secondary pressure injury via radial dispersion of force.Above all,quantitative anatomical distance between the important landmarks were obtained,and these landmarks consisted of infundibular recess,mammillary bodies,cerebral aqueduct and suprapineal recess.These quantitative values to be measured included the distances between both medidal walls of thalamus,between infundibular recess and aqueduct,and between suprapineal recess and aqueduct.The anatomical distance between two landmarks was measured using the Ruler tool of Adobe Photoshop CS6.A 1-cm tape measure with scale was placed between two landmarks to be measured,ensuring that the tape measure and two landmarks were in the same plane and depth.The actual length of“ab”can be obtained by the following equal proportion equation,“ab/AB=cd/CD”.The virtual values of“AB”and“CD”could be gained by the ruler tool of Photoshop,and two points in the tape measure defined the actual value of“cd”.Meanwhile,through the above measurement processes,we can measure the diameters of the important anatomic landmarks of the third ventricle,which included Foramen of Monro,column of fornix,cerebral aqueduct,posterior commissure and pineal body.Moreover,the exposure and surgical operability of three approaches were evaluated by five endoscopic neurosurgeons according to the rating scale(Score:0-4,0:No exposure;1:Limited exposure,surgical maneuvers are not possible;2:Multiangled exposure,surgical maneuvers are difficult;3:Limited exposure,surgical maneuvers are possible;4:Multiangled exposure,surgical maneuvers are facilitated).Meanwhile,in order to increase the reliability of quantitative anatomic analysis,some objective quantitative values,area of surgical freedom and angle of attack,were also performed in this study.Area of surgical freedom was defined by two trapezoidal area,which were made up of 6 anatomic points on the floor of the third ventricle.In consideration of the short distance between two medial walls of thalamus(small angle of attack along the horizontal plane)and wide-angle of endoscope,there was little clinical significance to perform angle of attack in the horizontal plane during endoscopic approach to the third ventricle.Therefore,angle of attack was obtained from the maximum allowable viewing angle along the floor of the third ventricle(longitudinal plane).In addition,the anatomic structures from anterior to posterior(infundibular recess,mammillary body and aqueduct)in the floor of the third ventricle were not in the same depth during supraorbital SFTLT approach,and there was much measurement error of area of surgical freedom and angle of attack.Hence,these two objective quantitative values were only performed in TCTC and TFTC approaches.Results:The mediolateral(between the medial walls of thalamus),anteroposterior(including two parts,AM:between aqueduct and mammillary body;IM:between infundibular recess and mammillary body)and superoinferior(between suprapineal recess and aqueduct)distance of purely endoscopic TCTC,TFTC and SFTLT approaches were 4.0±1.0,4.2±0.4,4.1±1.1mm;17.3±1.4,17.6±0.5,12.8±3.3mm(AM);7.7±0.3,7.8±0.5 mm,not measured(IM);and 5.6±0.3,7.8±0.8,7.8±1.5mm,respectively.Meanwhile,the mean diameters of Foramen of Monro,column fornix,cerebral aqueduct,posterior commissure and pineal body of endoscopic TCTC and TFTC approaches were4.4±0.6,4.5±0.8 mm;1.8±0.2,1.7±0.3 mm;1.1±0.2,1.2±0.1 mm;2.5±0.4,2.6±0.5 mm;1.6±0.1,1.8±0.2 mm,respectively.In the aspect of five endoscopic neurosurgeons’evaluating the exposure and surgical maneuverability of three approaches according to the rating scale,the majority of exposed landmarks of TCTC approach(choroid plexus,medial wall of thalamus,Foramen of Monro,column fornix,cerebral aqueduct,tuber cinereum,mammillary bodies,posterior commissure,pineal body,pineal recess)were scored a“4”,and the infundibular recess was scored a“3”,because it was at the very front of surgical field.These above results were similar to TFTC approach.During the SFTLT approach,apart from the unexposed roof(choroid plexus,Foramen of Monro and column fornix),most of the landmarks were scored a“4”except for the infundibular recess,which was scored a“3”,because infundibular recess was posterosuperior to working channel.Due to the long surgical channel and blind area above the head-end of endoscope,it was necessary to manipulate gently to prevent the injury of some important neurovascular structures,anterior cerebral complex,optic chiasm,hypothalamus and thalamus,etc.As to the objective quantitative analysis,the mean area of surgical freedom of TCTC(0°endoscope:220±47;30°:247±56mm~2)was not significantly different from that of TFTC approach(0°endoscope:216±49;30°:245±53mm~2)under same endoscope,P>0.05.However,mean angle of attack of TCTC(0°endoscope:21±4°;30°:26±4°)was significantly larger than that of TFTC approach(0°endoscope:16±3°;30°:19±3°),P<0.05.Conclusions:Purely endoscopic TCTC and TFTC approaches both offer brilliant exposure of the anterior,middle and posterior third ventricle.Notably,TCTC approach with more straight surgical channel may have better surgical maneuverability than TFTC approach with lateral working channel.Despite the long working distance,the whole third ventricle are exposed well except for the roof in the SFTLT approach.Surgical manipulation can be accomplished smoothly,and these manipulation should be gentle to protect the important neurovascular structures around the surgical field. |
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