Neuroanatomy, Neuroimaging Study Of The Insular Regions, And The Role Of The Insular Cortex In Epilepsy

BackgroundIn humans,the insula is a highly developed structure,totally encased within the brain.The insular cortex is involved in memory,drive,affect,higher autonomic control,gustation,and olfaction functions.In addition,it is closely associated with many diseases.The insular has been implicated in the failure rate after temporal lobe resections.However,the full and comprehensive role that it plays continues to remain obscure.Our studies were divided into three parts as follows:PARTâ… Microsurgical anatomy and surgical approach of the insular lobe and related regionsObjectiveResection of the insula lesion remains a challenge for neurosurgeons because the insula is surrounded by critical vascular and neural structures. Knowledge of the anatomy will contribute to preoperative planning and to subsequent successful realization of surgical strategy.In addition,the human insula intervene between the brain superficial and deep structure.This may make the insula to become a surgical trajectory to other brain regions,a detailed and discerning account of the anatomy of the insular region will be helpful in selective the surgical approaches to deep-seated lesions.This study was to investigate systematically the detailed topographic anatomy,arterial supply,and venous drainage of the insular regions and related surgical approaches,to assist in the process of conceptualizing a reliable surgical approach to allow for a successful course of surgery.Methods10%formalin-fixed adult brain specimens 20(40 hemispheres),ten simply formalin-fixed,and the cerebral arteries of ten brain specimens were perfused with colored silicone,and they were dissected with the aid of the operating microscope by using×6 to×40 magnification.Observed and examined the bridging veins of the temporal lobes,the sylvian fissure;opened the entire sylvian fissure,examined the anatomical variations of the sulci and gyri of the insula;described insular area artery's supply and vein's pattern of drainage; simulated transylian-transinsular approach;compared four approaches to the ambient cistern,special attention was paid to the anatomic structures limiting visualization in each approach;Removal of the orbitofrontal,frontoparietal,and temporal opercula revealed the MCA;eventually,entire removal the hemisphere to detail observes related structure.In addition,The 6 brain specimens were dissected in the sagittal,axial,and coronal plane by sequential,incremental removal of tissue.Because the emphasis of the studies was different,the quantity of the brain specimens had a little variance.Results1.The opercula cover and enclose the insula.The anterior,superior,and inferior limiting sulci clearly demarcate the insula and distinguish it from surrounding cortical areas.The limen insula is located in the depths of the sylvian fissure and constitutes the anterobasal portion of the insula.A central insular sulcus divides the insula into two portions,the anterior insula(larger) and the posterior insula(smaller).The anterior insula was found to be connected exclusively to the frontal lobe,whereas the posterior insula was connected to both the parietal and temporal lobes.2.The MCA provides the sole supply to the insula.Predominantly from the M₂ segment,occasionally M₁ and M₃ segment,supplied the region of the insula.The majority of insular arteries supplied the insular cortex and extreme capsule,but not the putamen,globus pallidus,or internal capsule;the minority of insular arteries also supplied the claustrum and external capsule.The insular have been main four veins according to their relationship with the insular sulci and gyri:anterior,precentral,central,and posterior veins.Insular veins drained predominantly to the deep middle cerebral vein,although frequent connections to the superficial venous system were found.3.The vein of Labbémajor located in middle or posterior temporal veins drainage regions,12.5%located in anterior temporal veins drainage regions. The human insula locates on the base of the sylvian fissure;opening specific portions of the sylvian fissure can expose different parts of the insula.The mean distance between inferior limiting sulci and temporal Horn of the lateral ventricle is 6.5mm.Make a cortical incision in the inferior limiting sulcus to access to the temporal horn,the temporal stem can be injured.The longer the inferior limiting sulcus,the shorter the incision,the better for preservation the temporal stems;choroidal fissure is located between the thalamus and fornix, opening the temporal portion of the choroidal fissure can expose the perimesencephalic cisterns(posterior crural,ambient,and proximal quadrigeminal cisterns).The position relation of the parahippocampal gyrus and the lesion is key to selective this approach.4.The ambient cistern extends from the posterior margin of the crural cistern to the lateral edge of the midbrain colliculi,and round the lateral surface of the upper portion of the brainstem.The vein of Labbéand the parahippocampal gyrus obstacle to exposure through the subtemporal approach;the transtemporal transchoroidal approaches exposed the upper half of the ambient cistern,its major drawback is the need to perform a corticectomy in the temporal lobe.In addition,the vein of Labbéextended far enough anteriorly to limit the cortical incision in the temporal lobe.The transinsular transchoroidal exposed the anterior upper half of the ambient cistern.Its major disadvantage is damage the temporal stem;the occipital transtentorial approaches exposed the posterior lower half of the ambient cistern,the parahippocampal gyrus also blocked to exposure through this approach.Conclusions1.Knowledge of the topographic anatomy,arterial,and venous relationships of the insula will assist neurosurgeons in dealing with disorders in this area. 2.Arteries of supplying the insular originate from the middle cerebral artery, predominantly the M₂ segment.Insular veins drained predominantly to the deep middle cerebral vein,often could found connections to the superficial venous system.3.Drainage style of the bridging veins of temporal lobe is multiform.Anterior drainage of the vein of Labbéis a special type of the temporal vein,which is of clinical significance in operative exposure.It is recommended to preserve all venous structures during surgical approaches.4.The trans-insular approach can be used for lesions of basal ganglia regions,medial temporal lobe,and perimesencephalic cisterns.The major disadvantage of this approach is damage the temporal stem.If the lesion locate above the parahippocampal gyrus(upper part of ambient cistern),and the midpoint of the rounded medial edge of the parahippocampal gyrus is higher,should not to make a cortical incision in the cortex of temporal lobe (dominance hemisphere),may to selective the transinsular transchoroidal.5.Surgical approaches to lesions of the ambient cistern must be tailored to the site of the pathological findings.Position of the vein of Labbé,and the midpoint of the rounded medial edge of the parahippocampal gyrus,is key to determine surgical approach.The subtemporal approach allow for excellent exposure of the lower half of the ambient cistern;the transtemporal transchoroidal approaches suitable to exposed the upper half of the ambient cistern of non-dominance hemisphere;the transtemporal transchoroidal approaches exposed the upper half of the ambient cistern of non-dominance hemisphere;the occipital transtentorial approaches exposed the posterior lower half of the ambient cistern.PARTâ…¡MR and DTI study of the insular and related regionsObjectiveThe insula is seen on every MR imaging study of the brain.Familiarity with insular anatomy is important for diagnosis and functional MR imaging,Studies of insular anatomy have been reported previously,primarily in the surgical literature.However,little has been published in the radiologic literature.The temporal stem lying the inferior limiting:sulcus of the insula and the lateral superior margin of the temporal horn,it is the white matter bridge between the anterior temporal lobe and the thalamus,the brainstem and the frontal lobe.This structure is also a critical landmark and surgical trajectory of transinsular to the temporal horn.This injury in the temporal stem can result in various cognitive deficits and/or visual field defects.The temporal stem contains several white matter tracts.The anterior limit of the temporal stem is the amygdaloid body,and the posterior limit is the lateral geniculate body. However,it is difficult to identify these fiber tracts and landmarks in MR studies and surgical fields.This study was to observe the topographic anatomy of the insular region, analysis MR images appearance,and definite suitable landmark.Guide function research and clinical diagnose and therapy in insular region.And to define the three-dimensional relationships of the uncinate fasciculus,anterior commissure,inferior occipitofrontal fasciculus,and optic radiation,to determine the positioning landmarks of these white matter tracts by using the diffusion tensor tractography(DTT).Methods1.To study the insular anatomy in 12 human cadaveric,analyzed the patterns of insular on the 1.5-T MRI of 160 insular,to the vertical planes perpendicular to the Talairach-Tournoux baseline at the anterior commissure (VAC)and posterior commissure(VPC);and appropriate landmarks for the anterior border,apex,and posterior border of the insula.In each subject,the coronal planes perpendicular to the AC-PC line at the AC(VAC)and PC(VPC)were established at the midline and projected onto the insulae laterally,to definite its relationship to the insula.2.DTT was performed on 10 healthy volunteers.Tractographies of the temporal stem was performed by using of the regions-of-interest(ROI) approach based on the anatomic knowledge and conventional MRI,by stepwise decreasing the regions of interest.And To reconstruct the individual fiber tracts of the temporal stem,we used a multiple ROIs approach to exploit existing anatomic characteristics of the tract trajectories.Results1.Axial MRI,the most cases,junctions of the internal and external capsules defined the anterior border of the insular.Sagittal MRI,The insular is separated from the opercula by the limiting sulci,the anterior surface of the most medial portion of HG marked the posterior border of the insula;Coronal MRI,the anterior lobule maintained a dorsal position in relation to the posterior lobule. The central sulcus was the inferior border of the anterior lobule and the superior border of the posterior lobule;VAC intersects usually at the precentral sulcus.VPC demarcates the posterior insular border.2.The anterior tip of the temporal horn was covered by optic radiation along its lateral half;The lateral wall of the temporal horn was covered by optic radiation;the medial wall of the temporal horn was free from optic radiation, except at the level of the lateral geniculate body;the entire superior wall of the temporal horn was covered by optic radiation;the entire inferior wall of the temporal horn was free from optic radiation.The optic radiations converge in the stratum sagittale,which flanks the lateral wall of the lateral ventricle in the depth of the superior and middle temporal gyrus.3.The temporal stem contains the uncinate fasciculus,inferior occipitofrontal fasciculus,anterior commissure,optic radiation,and inferior thalamic peduncle.It begins at the limen insulae and ends at the posteroinferior insular point,length averaged 32.95mm(range 30～40 mm). The posteroinferior insular point is the anterior extremity of intersection of the Heschl's gyrus and the inferior limiting sulcus.The shortest of distance from inferior limiting sulcus to the temporal horn regards as approximation thickness of the temporal stem.The distance from the limen insulae to the tip of the temporal horn averaged 10.9 mm(range 9～14 mm).The uncinate fasciculus and anterior commissure occupy the anterior one third of the temporal stem. The inferior occipitofrontal fasciculus passes through entire temporal stem. The anterior extent of Meyer's loop is located between the anterior tip of the temporal horn and limen insulea.However,most of the optic radiation cross the postmedian two third of the temporal stem,transect this region would complete injure the optic radiation.Conclusions1.1.5T MR images can demonstrable detailed anatomical study of the insular region,precise reproducible and evaluate patterns of anatomy.2.The optic radiation flanks the lateral wall of the lateral ventricle in the depth of the superior and middle temporal gyrus.Transsylvian and fusiform gyrus approaches will avoid damage to the optic radiation,whereas through the superior and middle temporal gyri will traverse the optic radiation.3.The primary configuration of the temporal stem is similar among the individuals studied.However,the temporal stem showed a considerable inter-individual difference in its size and shape.The limen insulae,anterior tip of the temporal horn,and posteroinferior insular point may be used to localize the temporal stem in analyzing MR imaging or during surgery.PARTâ…¢Correlation between the Rats Fully-kindled Insular and Amygdaloid Model of EpilepsyObjectiveTemporal lobe epilepsy is the most common disorder;the insular has been implicated in the failure rate after temporal lobe resections.However,the investigation is lack of the relation between the insula and the temporal lobe epilepsy.The study of the insular lobe epilepsy is necessary to further improve the therapeutic effect of the epilepsy surgical operation.The purpose of this study was to delineate the connection between the insular with amygdale on the seizure. MethodsTo establish the electrical Stimulation fully-kindled seizures amygdala and insular models,give microinjections of procaine into the ipsilateral insular or amygdala,If the electrodes were implanted into insular,procaine was injected into-amygdala;and if the electrodes were implanted into amygdala,procaine into insular.Investigate the interaction of microinjections of procaine on the amygdala and insular.ResultsThe injection of procaine into the amygdale could significantly suppress kindled seizure of insular;while into the insular could suppress the amygdale. For the suppressed rats,elevating the intensity of stimulation can evoke the generalized stage-5 seizure.The seizure appearance and generalized seizure duration were also similar to that in the control group.ConclusionsThe results of the present study suggest the relationship between the amygdala and ipsilateral insular might be understood as "a focus complex". Stimulations to the AM simultaneously activate the ipsilateral insular,and the amygdala is also an integral and necessary structure for the expression of kindled seizures elicited from the insular.