The Study On The Microsurgical Anatomy And Operative Approaches Of The Medial Temporal Region

Objective 1.To explore the anatomy of mesial temporal lobe and the relationshipsbetween the mesial temporal lobe and its surrounding structures.2.To study theapproaches to the medial temporal region.3.To investigate the blood supplying of theadjacent structures of the ambient cistem,particulaly the medial temporal region.Methods 1.Fifteen formalin—fixed adult cadaveric heads specimens after perfusionof the arteries and veins with colored silicone and thirty cerebral hemispheres werestudied under microscope,and photographs were taken from different angle.Theanatomic structures of the medial temporal region and the relationships among theadjacent structures,internal carotid artery,anterior choroidal artery,posteriorcommunicating artery,Rothensal vein,were studied.2 Transverse lines at the level ofthe inferior choroidal point and quadrigeminal plate were used to divide the medialtemporal region into anterior,middle,and posterior portions.Surgical approaches tothe medial temporal region were classified into four groups:superior,thetranssylvian-transinsular approach,lateral,the temporal transcortical or transsulciapproach,basal,the subtemporal approach,and medial,based on the surface of thelobe through which the approach was directed.The approaches through the medialgroup were subdivided further into an anterior approach,the transsylviantranscisternal approach,and two posterior approaches,the occipital interhemisphericand supracerebellar transtentorial approaches.All the approaches were maderespectively on fifteen cadaveric head specimens,the advantages and disagvantages ofthe approach were evaluated.The impact of temporal bridging veins,including itslocation,course and configuration,on the approaches were explored at the same time.Results 1.The parahippocampal gyrus separated from fusiform gyrus laterally bycollateral sulcus.The collateral sulcus was present in all 30 hemispheres.Thecollateral sulcus and the rhinal sulcus was constant in 24 sides,the remains were notconstant.The location of the collateral sulcus and consequently the location of thelateral part of the floor of the temporal hom can be determined by following theinferior temporal branches of the posterior cerebral artery as they descend into thedepth of the collateral sulcus before continuing on the surface of the basal temporal gyrus.2.The hippocampus and the fimbria occupies the medial part of the floor of thetemporal horn The hippocampus is 48.8mm±2.6mm long,including threeparts:head,body and tail.The transverse diameter and the anteroposterior diameter ofthe head of the hippocampus are 19.24±2.3mm,17.56±3.6mm,respectively.the bodyof the hippocampus is 24.42±4.6mm long;The transverse diameter and theanteroposterior diameter of the tail of the hippocampusare7.88±2.4mm,6.82±1.2mm,respectively.The head of the hippocampus characterizedby three or four hippocampal digitations is the only part of the hippocampus that isfree of choroid plexus.3.The amygdala can be considered as being entirely located within the boundaries ofthe uncus:superiorly,the temporal amygdala blends into the globus pallidus withoutany clear demarcation;inferiorly,the posterior portion of the amygdala bulgesinferiorly from the most anterior portion of the roof of the temporal horn toward thesuperior part of the hippocampal head,and frequently they become fused(90%).Theamygdala is the anterior wall of the temporal horn and also constitutes the mostanterior part of the roof of the temporal horn.4.The distance from the collateral sulcus to the temporal horn,which is the shortestdiatance among the distances between sulci and temporal horn,is 2.81±0.14mm at thelevel of the apex of the uncus and 3.19±0.65mm at the inferior choroidal point.Thedistance from the inferior limiting sulcus to the roof of temporal horn is6.08±1.32mm at the level of the apex of the uncus and 6.58±2.12mm at the inferiorchoroidal point.The average distance from the parahippocampal gyms to thetemporal horn is 6.80 mm at the level of the apex of uncusnand is 12.32 mm at thelevel of the inferior choroidal point.5 The choroidal fissure is located between the thalamus and fimbria;it begins at theinferior choroidal point behind the head of the hippocampus and constitutes themedial wall of the posterior two-thirds of the temporal horn.the highest point of theuncus is located at the end of its posteromedial surface,namely at the level of theinferior choroidal point,which is the important anatomic landmark in the temoral hornsurgery.The distances from the inferioe choroidal point to temporal polar,head of hippocampus and the apex of the uncus were 45.96mm,17.56mm,10.88mm,respectively.6.The proximal half of the cisternal segment of the anterior choroidal artery is relatedto the upper third of the anteromedial surface of the uncus in 73% of the cases,themiddle third of the anteromedial surface of the uncus in 9%,the inferior third of theanteromedial surface of the uncus in 18%;the distal half of the cisternal segment ofthe anterior choroidal artery is related to the upper third of the posteromedial surfaceof the uncus in 91% of the cases,the inferior third in 9%.The P2a segment of theposterior cerebral artery passes at the level of the uncal notch in 58% of thecases,above the level of the uncal notch in 33%,below the level of the uncal notch in9%.7.There are a total of 125 hippocampal arteries,for an average of 4.2 arteries perhemisphere(range two to seven arteries),originating from the posterior cerebralartery(PCA) and its branches in 74.4%,from AChA in 25.6%.A total of 26 (20.8 %)hippocampul arteries arise from anterior inferior temporal artery(AITA) in 25hemispheres;there are six unco-hippocampul arteries originating from AITA.Thebody and the tail of the hippocampus was supplied by vessels derived mainly fromPCA and its subtemporal branches,the hippocampul artery supplying the head of thehippocampus derived from the anterior choroidal artery (AchA).The inferior surfaceof the posterior segment of uncus was found to be the important anastomotic sitebetween the hippocampal branches of the AchA and the hippocampal branches of thePCA.8.The anterior portion of the medial temporal region can be reached through thetranssylvian-transinsular approach,the temporal transcortical or transsulci approach,the subtemporal approach,and transsylvian transcisternal approach.The middle partof the medial temporal region can be reached through the transsylvian-transcisternal,subtemporal and the lateral temporal approaches,where the approach must betailored according to the nature of the lesion and its extension to other medialtemporal areas.The posterior group of approaches directed through the medial surfaceare useful for lesions located in the posterior portion.9.There were 32 Labb(?) veins on 30 sides,1 Labb(?) per specimen was found on 28 sides,and 2 Labb(?)veins per side on 2.The diameter of Labb(?)was 2.68mm (range1.46to 4.32mm) and the length of the subtemporal segment of Labb(?) was 15.86mm(range15.20 to 16.72mm).The majority of the veins of Lab(?) were present at the regions ofthe posterior (53.1%) and middle temporal veins (40.6%),and only 6.3% wereobserved at the region of the anterior temporal veins.The locations of termination ofthe Labb(?) on the transverse sinus in 62.5% of the cases,the posterior tentorial regionin 18.75%,the anterior tentorial region 18.75%,respectively.The distance from leftsino-dura point to the location of termination of Labb(?) was 19.84mm (range 5.28 to30.16mm),the right was 20.62mm (range 7.16 to 29.72mm).There were threeconfigurations,the separated type (25%),the bundle type (45%) and the multipletype (30%),defined as the temporal bridging veins,and the second type was themajor configurations.The locations of terminations of the bridging veins were dividedinto 4 groups:the transverse sinus group (55%),the posterior tentorial group (30%),the superior petrosal sinus group(9.4%),and the anterior tentorial group (5.6%).10.Resection of uncus can increase the scope of P2a exposed.Conclusion 1.The structures of the mesial temporal lobe are adjacent to MCA,AChA,brain stem,optic tract and BV,so understanding of the mesial temporal lobeanatomy and the relationships between the mesial temporal lobe and its surroundingstructures is conducive to the microsurgical operations of the mesial temporal lobelesions.Inferior choroidal point,choroidal fissure,the characteristic of the posteriorportion of the amygdala fused with the hippocampul head,are the important surgicallandmarks.2.Dividing the medial temporal region into smaller areas allows for amore precise analysis,not only of the expected anatomic relationships,but also of thepossible choices for the safe resection of the lesion.3.Each approach to medialtemporal lesions has technical or functional drawbacks and combination ofapproaches that should be considered when selecting a surgical treatment for a givenpatient.4.Partial resection of uncus may be used as a method to expose the anteriorportion of medial temporal region.