Microsurgical Anatomy Of Arachnoid Membranes In Pineal Region And Clinical Research

Objective：It’s to demonstrate the arachnoid’s structure, ttachment pointsand the relationship with the surrounding structures in the pineal region,todiscuss the effections of the arachnoid membrane structure on tumorousgrowth direction and form,and to summarize the relationship between thetumor and arachnoid in the pineal region,also to provide a theoreticalguidance for choosing a appropriate surgical approach of the tumor resectionin the pineal region.Method:After cleaning the surface of the8cadaveric head Pecimens,weput them in the alcohol(60%),dissect and separate the vascular of theneck,flush them after Intubation and perfuse them With silicone.The cadavericheads were fixed in home-made head rack,Simulatiing the prone position.Thescalp incision was reach to mastoid process on both sides,top level to parietaltuber, Below the neck.We incised the scalp in full thickness,exposed the skull,removed the bone valve using electric drill,jigsaw,reserved the transversesinus and sagittal sinus,cut open the dura mater,and then removed the parietallobe, occipital lobe,parts of the thalamus,corpus callosum and so on underingthe microscope.It shoud be carefully dissecte them so as to expose thearachnoid and the pia mater surrounding in pineal region.When observing thestructure,origin and attachment points of arachnoid in pineal region,we takepictures to record the important structures.Analyse the image Materials andoperation methods of20cases of pineal region tumors.Discusses the effectionof arachnoid membrane’s structure in pineal region on tumor growth directionand form.we can summarize that how to select a appropriate surgical approachaccording to the tumor shape and location further.Result:1The arachnoid membranes and cisterns in pineal region 1.1The arachnoidal envelope,arachnoid membranes covering theinferior-medial surface of occipital lobe and the superior surface of cerebellumconverge to form the arachnoidal envelope.1.2The posterior perimesencephalic membrane,it arises from the outerarachnoid membranes covering the inferior occipital lobe and the superiorcerebellum at the tentorial edge.1.3The cerebellar precentral membrane,It originates from the arachnoidmembrane covering the superior cerebellum where it meets with thearachnoidal sleevelet,and is attached to the inferior colliculus anteroinferiorly.1.4The quadrigeminal cistern,It’s borders the superior cerebellar cistern by thecerebellar precentral membrane,the posterior pericallosal cistern by thearachnoidal sleevelet and the posterior ambient cistern by the ascending partof the posterior perimesencephalic membrane.1.5Superior cerebellar cistern,below the straight sinus and above the cerebellarvermis.1.6The posterior ambient cistern,borders the cerebellomesencephalic cisternby the horizontal part of the posterior perimesencephalic membrane.1.7Cerebellomesencephalic cistern,between the ntral lobule, cerebellarpeduncle and idbrain tegmentum,extending from The middle to the sides.2Clinical cases:there were20cases which were operated by different ways ofoperation approach,such as:Occipital transtentorial approach,Infratentorialsupracerebellar approach,Posterior transcallosal approach andtranscallosal-septum pellucidum-interforniceal approach.There were only15cases can be cleared the location of the tumor base,2cases on splenium ofcorpus callosum,9cases on pineal body,3cases on quadrigeminal plate.Thetumors could be classified according to the basal position which can be seen inthe MRI or the surgical procedure:the base on pineal body;the base onquadrigeminal plate;the base on splenium of corpus callosum above the Galenvein.Conclusion:1The arachnoid membranes in pineal region contain the arachnoidal envelope,the posterior perimesencephalic membrane and the cerebellarprecentral membrane.The arachnoid membranes distinguish this region intoseveral cisterns, such as:The quadrigeminal cistern,uperior cerebellarcistern,the posterior ambient cistern, rebellomesencephalic cistern.2This experiment demonstrated that the superior arachnoid membrane ofthe arachnoidal envelope was usually easy to be separated from choroidmembranes above,but sometimes it was hard to,so it’s not entirely sure thatthay are two independent membranous structure;3The arachnoid membranes in pineal region have certain effect ontumorous growth direction and form to low invasive malignant tumor andbenign tumor,especially the arachnoidal envelope and the cerebellar precentralmembrane.4Because of the limitition of the arachnoidal envelope,we can choosetranscallosal-septum pellucidum-interforniceal approach when the pinealregion tumors grow forward into the third ventricle significantly.5According to the tumorous structural characteristics of imaging andarachnoid relationship,it will be helppful to select a right surgical approach.6The nature of the tumor plays a big role in the growth direction andpattern of Pineal region tumors,besides the influence of arachnoid membranestructure.This experiment drew the conclusion through the anatomy of thecadaver head specimens and the analysis of cases,so it needs to be studiedfurther so as to verificate the relationship of the arachnoid membrane structureand the tumor growth.