【作者】 樊俊；

【导师】 漆松涛；

【作者基本信息】 南方医科大学 ， 神经外科学， 2011， 博士

【摘要】 一、研究背景和目的环中脑区是指环绕中脑周边的区域,具体上可划分为中脑前区(脚间区)、中脑侧区和中脑后区(松果体区)。颞叶、枕叶、小脑幕、中脑及蛛网膜将环中脑区的蛛网膜下腔包围、分隔形成各组脑池,池内的蛛网膜与各种神经血管结构具有密切联系。环中脑区位置深在,包含后循环动脉、颅神经、中脑及Galen静脉系统等多种重要神经血管结构,是颅内解剖结构最为复杂的部分之一,多种颅内深部病变如松果体区肿瘤、脑膜瘤、三叉神经鞘瘤及后循环动脉瘤等均好发于该区域,此类病变对神经外科医生的显微解剖学知识和手术技巧构成巨大的挑战。因此,深入了解该区域的显微解剖学特点,对于该区域的各类病变的病理学基础,手术入路的设计以及具体的显微手术操作技巧具有重要意义。回顾历史文献,涉及环中脑区脑池的研究很多,但通常局限于池内的神经血管结构及相关的手术入路,对于构成脑池的蛛网膜结构的研究较少,且此类研究多数仅限于Liliequist膜等少数蛛网膜结构。国内外仅有吕健等、Rhoton等和Vinas等对于环中脑区的部分蛛网膜进行了描述,但研究尚不够详细与完善,且在关于各脑池的划分与蛛网膜的描述之间也存在着差异。例如,Rhoton等描述在幕切迹与桥-中脑交界处之间存在一层“桥中脑外侧膜”,以此分隔环池与桥小脑角池,而Vinas等则报道在幕切迹水平有一层“小脑上膜”,并认为该膜由后方的“小脑前中央膜”发出,环绕中脑并终止于动眼神经,将环池分隔为上下两部分；Rhoton等和Vinas等还提及松果体区的Galen静脉被一层蛛网膜袖套所包裹,但仅对此结构进行了粗略的描述,未做更进一步的研究；此外,绝大部分文献认为环池是一个跨越小脑幕上下空间的脑池,有的作者甚至将其分为幕上下两部分。针对以上问题,我们对环中脑区的蛛网膜与脑池重新进行了细致的显微解剖学研究,以期对该区域的蛛网膜和脑池能有一个全面、系统的认识,同时还希望有助于分析影响该区域各类病变发生-发展模式的因素,以及对于实际的显微手术操作有所指导意义。二、材料与方法1、实验材料：成人头颅标本20个,10%福尔马林浸泡固定,肉眼观察均未发现颅内病变或畸形。显微手术器械、显微镜及录像系统。2、实验方法：(1)随机选取10例标本进行尸头血管灌注。(2)尸头解剖：沿眉弓-枕外隆突连线锯开颅盖骨,分离颅骨与硬膜粘连,去除颅盖骨,沿上矢状窦旁两侧约1cm剪开硬膜,呈瓣状翻向下方,暴露双侧大脑半球。在手术显微镜下,去除半球面的脑实质-软膜-蛛网膜,沿断端软脑膜下逐步剔除脑实质,深部至侧脑室壁、胼胝体及脑干面,完整保留大脑镰侧及颅底侧的软膜-蛛网膜。脑实质剔除之后,沿环中脑区逐步剥除粘连于蛛网膜上的软膜,在剥离过程中同时观察蛛网膜与软脑膜之间的关系。因部分区域的蛛网膜与软脑膜粘连紧密,需细致分离,以免破坏蛛网膜结构,同时定期冲水,防止蛛网膜因干燥而皱缩,影响观察结果。软脑膜完全剥离之后,遂开始逐层解剖环中脑区的蛛网膜及其周边神经血管结构,同时对各脑池的蛛网膜构成、形态与边界、内容物及其与周边脑池的相互交通情况进行观察。其间,手术显微镜连接录像系统,对显微解剖过程进行视频记录,录像存档备用。三、结果环中脑区的内层蛛网膜包括环中脑膜、Liliequist膜,包裹Galen静脉系统的蛛网膜袖套(AEPG)及小脑前中央膜。1、环中脑膜：覆盖于颞枕叶底面和小脑上表面的外层蛛网膜在幕切迹处汇合,连同覆盖鞍背的外层蛛网膜环绕整个中脑发出一层较为完整的蛛网膜分隔,称为环中脑膜。该膜通常在近端较为完整与厚实,至远端则逐渐变薄并呈小梁状结构,可分为环中脑前膜和后膜两个部分：(1)环中脑前膜：即为Liliequist膜的中脑叶部分,位于大脑脚、鞍背及两侧幕切迹之间,以动眼神经为界,可分为内、外侧两段。内侧段通常呈松散的渔网状结构,其后缘通过一些蛛网膜束带附着于中脑-桥脑结合部及基底动脉分叉处。外侧段通常较厚、完整,未见明显的网孔,其内侧缘通常游离并紧贴大脑脚后行、变窄,最终在大脑脚后缘附近通过一些蛛网膜小梁与环中脑后膜相连。(2)环中脑后膜：位于中脑被盖部的后外侧,可分为水平段与升段。水平段的前缘通过一些小梁附着于中脑被盖或大脑大静脉,主要分隔环池后部与幕下的小脑中脑裂池。升段的前缘附着于丘脑枕外侧,上缘附着于包裹Galen静脉的蛛网膜袖套。该膜的前缘存在较大的网孔,从而使得四叠体池与环池后部之间存在着较大的交通范围。2、Liliequist膜：由覆盖后床突与鞍背处的外层蛛网膜发出并行向后上方,该膜大多数在其起始部或距起始部不远处分为两叶,即间脑叶和中脑叶：(1)间脑叶：由Liliequist膜发出后继续行向后上方,最终在乳头体附近附着于三脑室底,以分隔视交叉池和脚间池。该叶通常较为完整和致密,鲜有网孔存在。(2)中脑叶：即环中脑前膜。3、AEPG：覆盖于枕叶底面、内侧面及小脑上表面的外层蛛网膜在Galen静脉汇入直窦的小脑幕尖处逐步增厚、汇合形成一束袖套样结构,向前包裹Galen静脉及其属支近端、松果体及松果体上隐窝,称为包裹Galen静脉系统的蛛网膜袖套(AEPG)。以大脑内静脉分叉处为界,AEPG可分为前后两段：(1)AEPG后段(pAEPG):主要包裹Galen静脉及其属支近端,相对较厚。在Galen静脉汇入直窦处,pAEPG的后缘形成一个袖口,根据袖口与小脑幕尖之间的距离关系,可将其分为Ⅰ、Ⅱ两种类型。蛛网膜袖口的下缘明显增厚,可呈结节状压迫Galen静脉管腔,也可略为突起。(2)aAEPG：随大脑内静脉及松果体上隐窝进入三脑室后部,相对较薄,主要包含大脑内静脉的近端、松果体静脉、松果体上隐窝及松果体。4、小脑前中央膜：由pAEPG的下表面靠近袖口处向前下方发出,前缘通常附着于上丘表面或上下丘之间的软膜上,两侧附着于环中脑后膜的升段。此膜主要分隔前上方的四叠体池与后下方的小脑上池,通常较为完整和致密,少有网孔存在。上蚓静脉通常贴于小脑前中央膜的后侧上行,穿pAEPG下方汇入Galen静脉。环中脑区的脑池包括脚间池、动眼神经池、环池、小脑中脑裂池、四叠体池、小脑上池及中间帆池。1、脚间池：呈锥形,位于两侧的大脑脚与后穿质之间,由大脑脚、后穿质、三脑室底后部及Liliequist膜的两叶围绕形成,其边界可分为4个壁：(1)前壁由Liliequist膜间脑叶的前下段构成；(2)顶壁的间脑部分由Liliequist膜间脑叶的后上段及乳头体构成,中脑部分从乳头体的后缘一直延伸至脚间窝；(3)后上壁由脚间窝、大脑脚及后穿质构成,后下壁由桥脑上表面的部分构成；(4)底壁由Liliequist膜中脑叶构成；(5)外侧壁通常无完整的蛛网膜分隔,主要由动眼神经及部分蛛网膜小梁构成。脚间池的内容物包括基底动脉分叉部、大脑后动脉P1段、丘脑后穿支动脉、后交通动脉、大脑脚静脉、后交通静脉及桥中脑静脉等。脚间池前方通过间脑叶与视交叉池交通,下方通过中脑叶(环中脑前膜内侧段)与桥前池交通,两侧则通过一些稀疏的蛛网膜小梁与动眼神经池及环池前部交通。2、动眼神经池：位于脚间池与环池前部之间,环中脑膜、Liliequist间脑叶、颈动脉内侧膜及桥脑前膜发出一些蛛网膜小梁附着并包裹动眼神经,在动眼神经周边形成一个鞘样结构,从而构成动眼神经池。该蛛网膜鞘相对较薄,且多数不完整,动眼神经为动眼神经池内的唯一内容物。3、环池：是环绕中脑的一对脑池,呈前后宽、中间窄的半环形,位于小脑幕切迹以上水平、环中脑膜的上方,该池由颞叶内侧面、枕叶底面、中脑及环中脑膜围绕形成,从前方的颞叶钩回后缘一直延伸至后方的四叠体板外侧缘。环池可分为前后两部分：(1)环池前部：大脑脚外侧面及视束下表面的软膜与钩回软膜逐步融合,在进入脉络裂之前形成一个反折,共同构成环池前部的顶壁；底壁由环中脑前膜的外侧段构成,并籍此与下方的桥小脑角池分隔；内侧壁由大脑脚外侧面构成；外侧壁由颞叶内侧面构成。环池前部的前方与颈内动脉池交通,内侧与脚间池交通,内下方与动眼神经池交通,下方通过环中脑前膜的外侧段与桥小脑角池交通。(2)环池后部：中脑被盖、外侧膝状体与枕叶底内侧面的软膜逐步融合,在进入脉络裂之前形成一个反折,共同构成环池后部的顶壁；底壁由环中脑前膜的水平段构成,并籍此与下方的小脑中脑裂池分隔；内侧壁由中脑被盖的上部与外侧膝状体构成；外侧壁由枕叶底内侧面构成；后内侧壁由环中脑后膜的升段构成,藉此壁与四叠体池分隔。环池后部的后内侧通过环中脑后膜的升段与四叠体池交通,下方通过环中脑后膜的水平段与小脑中脑裂池交通,其中滑车神经即行于小脑中脑裂池内。环池内主要包括脉络膜前动脉、大脑后动脉、基底静脉,有时可见部分小脑上动脉。4、小脑中脑裂池：为幕下脑池,位于小脑脚上方、中央小叶、中央叶翼与中脑背侧之间,从两侧向中线呈翼状汇合,可分为中间部与外侧部：(1)中间部：位于中央小叶前下方,是一个潜在腔隙,前壁为小脑舌叶,后壁为中央小叶；该部分脑池内包含滑车神经及部分分支血管,其上方与小脑上池交通。(2)外侧部：位于中央叶翼前方,前壁为中脑背侧下部,后壁为中央叶翼,顶壁为环中脑膜后膜水平段,底壁为小脑上脚；该部分脑池内包含小脑上动脉及滑车神经,其上方通过环中脑后膜水平段与环池后部交通,前方与桥小脑角池交通。5、四叠体池：位于Galen静脉蛛网膜袖套的下方,具有前、后、上、外侧5个壁。上壁由Galen静脉蛛网膜袖套构成,前壁的中间部分由四叠体板(上下丘)构成,两侧部分由丘脑枕内侧面构成,后壁由小脑前中央膜构成,外侧壁由两侧的环中脑后膜升段构成。池内包含脉络膜后内侧动脉及中脑背侧的一些分支血管。脉络膜后内侧动脉在四叠体池外侧穿环中脑后膜的升段进入四叠体池,贴丘脑枕内侧走行,最后在丘脑枕内侧面与蛛网膜袖套之间进入中间帆腔内。四叠体池两侧通过环中脑后膜的升段与环池后部交通,两池之间通常仅有疏松的蛛网膜小梁间隔,网孔较大；后方通过小脑前中央膜与小脑上池交通；上方通过两侧丘脑枕内侧面与蛛网膜袖套之间的间隙与后胼周池交通。6、小脑上池：位于小脑蚓上方,可分为前后两个部分：(1)蚓前部：位于小脑蚓中央小叶的前方,前壁为小脑前中央膜及下丘下部,后壁为中央小叶,侧上壁为部分环中脑后膜；池内包含蚓上静脉及小脑上动脉的分支；该部分脑池的下方通过一些稀疏的蛛网膜小梁与小脑中脑裂池交通,前方通过小脑前中央膜与四叠体池相隔。(2)蚓后部：位于小脑蚓山顶和山坡的上方,上壁为小脑上表面蛛网膜,下壁为山顶和山坡,池内包含小脑上动脉的小脑分支；该部分脑池在两侧与小脑半球表面的脑池交通,在后方与枕大池交通。7、中间帆池：位于三脑室的顶部,由脉络膜的上下两层构成,上层紧贴穹窿,向后与胼胝体压部的软膜相延续,下层后部延续为松果体上隐窝。池内主要包含大脑内静脉远端及脉络膜后内侧动脉,其中大脑内静脉包裹着二级蛛网膜袖套。中间帆池的后方处于开放状态,可与后胼周池交通,但与脑室系统之间不存在交通关系。四、结论我们对环中脑区的蛛网膜和脑池重新进行了详细的显微解剖学研究,与以往的文献相比,获得了以下一些新的认识：1、明确并命名了环中脑膜,并对其的组成、形态、分布特点及变异情况进行了详细描述。2、确定了Liliequist膜中脑叶的外侧边界。3、对包裹Galen静脉系统的蛛网膜袖套(AEPG)进行了系统的阐述。4、明确了小脑前中央膜的概念,并对其形态学特点、分布形式进行了描述。5、从解剖学角度证实了环池是一个位于幕上的脑池,该池位于环中脑膜以上水平,并藉此膜与幕下脑池相分隔。6、重新划分了各脑池的分布范围、内容物及相互间的交通关系。7、蛛网膜结构可能是影响环中脑区肿瘤的生长方式的重要因素之一,充分认识其解剖学特点可为探索该区域肿瘤新的分型方法提供解剖学依据。8、环中脑区各种类型的病变及其周围的神经血管结构与蛛网膜及脑池之间存在密切关系,了解这一关系对于手术入路的设计和显微手术操作有重要意义。更多还原

【Abstract】 Background and ObjectiveThe perimesencephalic region refers to the area surrounding the midbrain. Specifically, it can be divided into anterior (interpeduncular), lateral and posterior (pineal) mesencephalic region. The subarachnoid space of the perimesencephalic region is surrounded by the temporal lobe, occipital lobe, tentorial incisura, midbrain and inner arachnoid membrane, forming cisterns, in which the arachnoid membranes are closely related to adjacent neurovascular structures. The perimesencephalic region is one of the most complex areas lying deep within the brain and containing arteries, deep veins, cranial nerves and brainstem. Many lesions like germinomas, meningiomas, trigeminal neurinomas and aneurysms frequently arise from the region, presenting unique challenges to the neurosurgeon about the knowledge of the anatomy and management. For this reason, a complete understanding of the microsurgical anatomic features in this region play an important role inVarious descriptions of the ambient cistern can be found in the literature, and the anatomy of neurovascular structures or surgical approaches in this region has been well illustrated. However, only few microscopic studies of the arachnoid membranes related to the region have been published, which is limited to such structures as Liliequist’s membrane. Lu, Rothon and Vinas have described some aspects of the arachnoid membranes in the perimesencephalic region. However, they had not make a detailed and complete description, and there still exist some conflict among their illustration about the arachnoid membranes and cisterns. For example, Rhoton identified, lateral to the oculomotor nerve, a "lateral pontomesencephalic membrane" that was "attached to the pontomesencephalic junction and to the outer arachnoidal membrane near the free edge of the tentorium." They demonstrated that this membrane separated the cerebellopontine from the ambient cistern. But Vinas identified a membrane, the "superior cerebellar membrane" that originates "from the cerebellar precentral membrane and runs around the midbrain towards the oculomotor cistern." Rhoton and Vinas also mentioned that the vein of Galen and its tributaries are surrounded by a broad membranous envelope, while they failed to provide further description about it. In addition, most authors have considered the ambient cistern to be a subarachnoid space extending across the tentorial incisura. Some authors even divided the cistern into supra- and infratentorial compartments.Focused on the above-mentioned issues, we reinvestigated the anatomy of the arachnoid membranes and cisterns in the perimesencephalic region in an attempt to gain a thorough understanding about it. Hopefully, it will be helpful to explore some factors possibly related to the growth of lesions in this region and more precisely manage lesions in this region.Materials and MethodsMaterials:Twenty adult cadaveric brains fixed in formaldehyde solution were carefully prepared for microsurgical dissection. On macroscopic examination, none of the brains showed signs of cerebral diseases. Some microsurgical instruments, a Leica surgical microscope and a digital video recorder were also used in this study.Methods:10 specimens were selected randomly and injected by color silicon through internal carotid artery and vein. The cranium of all 20 specimens was first removed at the level of line between the superciliary arch and the inion after the dura mater has been dissected from the skull. The dura mater was then opened along the line about lcm to the superior sagittal sinus and turned over downwards to expose bilateral hemispheres. The supratentorial cerebral lobes were subpially removed under a surgical microscope, step by step, until it reached the wall of ventricle, corpus callosum and brainstem. The leptomeninges near the falx and the skull base was totally reserved. After the brain parenchyma was removed, the pia mater was then carefully dissected away from the surfaces of the arachnoid membranes surrounding the midbrain, with special attention to observe the relationship between the arachnoid membrane and the pia mater. It is important to handle tenderly in some region where the arachnoid membrane was adhered tightly to the pia matter, in case of the destruction of the membrane. Some timely irrigation also prevents the membrane from shrinking which may lead to an incorrect result. Finally, the arachnoid membranes with their adjacent neurovascular structures in the perimesencephalic region were carefully dissected. During the whole course of the study, the microscope was connected to the digital video recorder for photographic documentation. The cisterns and their arachnoid membranes, configurations, borders, contents, and communications with adjacent cisterns were examined in detail in this study.ResultsThe inner arachnoid membranes in the perimesencephalic region include the perimesencephalic membrane, Liliequist’s membrane, the arachnoid envelope surrounding the vein of Galen (AEPG) and the precentral cerebellar membrane.Perimesencephalic membrane. The perimesencephalic membrane is a set of inner arachnoid membranes surrounding the midbrain at the level of the tentorial incisura. It originates from the outer arachnoidal membrane covering the tentorial edge and the dorsum sellae. This membrane usually changes in structure from an intact and thick membrane to a thinner trabeculated membrane with many perforations near its attachment. The membrane is composed of 2 distinct membranes—anterior and posterior. The anterior membrane is actually the mesencephalic leaf of Liliequist membrane. It extends between the dorsum sellae and bilateral tentorial edges. The oculomotor nerve divides it into medial and lateral parts. The medial part extends posteriorly with a free edge attaching to the basilar bifurcation and the junction of the midbrain and pons by trabeculae. This part usually presents as a structure of trabecular network with large perforations. The lateral part is frequently intact without perforations. As it extends backward, the lateral part becomes narrow, gradually, until it disappears. The anterior and posterior membranes are mostly connected by some sparse trabeculae. The posterior membrane is surrounding the midbrain tegmentum and can be divided into horizontal and ascending parts. The horizontal part was attached anteriorly to the midbrain tegmentum or the basal vein. It separates the posterior ambient cistern from the cerebellomesencephalic cistern. The ascending part is attached anteriorly to the pulvinar and superiorly to the AEPG. The posterior membrane is mostly thinner and incomplete with multiple perforations near its attachment, which causes a wide communication between the ambient and quadrigeminal cistern.Liliequist’s membrane. Liliequist’s membrane arises from the arachnoid covering the dorsum sellae and posterior clinoid processes, and can be divided into two distinct leaves near its origination. The diencephalic leaf originates from Liliequist’s membrane, extends posterosuperiorly and attaches to the pia of the diencephalon between the infundibulum and mamillary bodies. The leaf is usually intact and complete without openings. The mesencephalic leaf refers to the anterior perimesencephalic membrane in this study.AEPG. The supratentorial outer arachnoid membrane covering the edial surface of bilateral parietooccipital lobes and the posterior urface of splenium and the infratentorial outer arachnoid embrane covering the superior surface of the cerebellum converged near the site where the vein of Galen emptied into the straight sinus. The thickened outer arachnoid membrane then embraced and ran forward along the vein of Galen to form the AEPG. The AEPG could be arbitrarily divided into 2 parts:anterior and posterior. Anterior AEPG (aAEPG) is relatively thick and encloses the great cerebral vein and its proximal tributaries. The posterior edge of pAEPG forms an arachnoid cuff near the site where the great cerebral vein joins the straight sinus. Based on the distance between the cuff and the tentorial apex, it can be divided into typeⅠand typeⅡ. Posterior AEPG (pAEPG) is relatively thin and contains the proximal inner cerebral vein, the pineal vein, the suprapineal recess and the pineal body. It enters the posterior compartment of the third ventricle together with the inner cerebral vein and the suprapineal recess.Precentral cerebellar membrane. The membrane originates from the lower surface of pAEPG near the cuff, extends anteroinferiorly, attaches to the quadrigeminal plate anteriorly and to the ascending part of the posterior perimesencephalic membrane laterally. This membrane is usually intact an complete with few perforations, separating the quadrigeminal cistern from the superior cerebellar cistern. The superior vermian vein runs upwards along the posterior edge of the membrane and perforates the lower surface of pAEPG to join the great cerebral vein.The cisterns in the perimesencephalic region include the interpeduncular cistern, the oculomotor cistern, the ambient cistern, the cerebellomesencephalic cistern, the quadrigeminal cistern and the superior cerebellar cistern.Interpeduncular cistern. The interpeduncular cistern is a pyramid-shaped compartment enclosed by the peduncle, the posterior perforated substance, the posterior diencephalon and both leaves of Liliequist’s membrane. It is located between the peduncle and the posterior perforated substance. Its anterior wall is formed by the anteroinferior part of the diencephalic leaf. The roof consists of diencephalic and mesencephalic parts:the diencephalic part refers to the posterior-superior part of the diencephalic leaf and the mamillary bodies, and the mesencephalic part refers to the upper surface of the interpeduncular fossa. The posterior wall is formed by the peduncle, the interpeduncular fossa and upper surface of the pons. The inferior will is formed by mesencephalic leaf. Its lateral wall usually presents as some trabeculae ro incomplete arachnoid septum attached to the oculomotor nerve. The content of the interpeduncular cistern includes the bifurcation of the basilar artery, the P1, the posterior thalamoperforating arteries, the posterior communicating artery with its branches, the peduncular vein and the posterior communicating vein. The interpeduncular cistern borders the chiasmatic cistern by the diencephalic leaf anteriorly and the prepontine cistern by the mesencephalic leaf inferiorly. Laterally, it communicates with the oculomotor cistern and the anterior ambient cistern via some sparse trabeculae.Oculomotor cistern. The diencephalic, mesencephalic, medial carotid, lateral pontomesencephalic, and anterior pontine membranes attach to form a sleeve, mostly thin and incomplete, around the nerve, constructing the oculomotor cistern. The cistern spans the interval of the interpeduncular and the ambient cistern. The oculomotor nerve is the only content of the cistern. It arises from the medial side of the peduncle, passes between the posterior cerebral and superior cerebellar arteries and courses anterolaterally at the junction of the carotid, interpeduncular, prepontine, and cerebellopontine cisterns to reach the dural roof of the cavernous sinus.Ambient cistern. The ambient cistern is a paired ring-shaped cistern situated above the level of the tentorial incisura and the perimesencephalic membrane. It is surrounded by the upper midbrain laterally in a semiring shape and is limited by the medial temporal lobe, the inferior occipital lobe, the midbrain, and the perimesencephalic membrane. The cistern can be divided into anterior and posterior compartments. The superior wall of the anterior compartment is formed by the pial layers covering the lateral surface of the upper peduncle, the optic tract, and the uncus. The inferior wall is formed by the lateral part of the anterior perimesencephalic membrane, the medial wall by the lateral peduncle, and the lateral wall by the medial temporal lobe. The anterior ambient cistern communicates with the carotid cistern anteriorly, the interpeduncular cistern medially, the cerebellopontine cistern inferiorly, and the oculomotor cistern inferomedially. The superior wall of the posterior compartment is is formed by the pial layers covering the midbrain tegmentum, the lateral geniculate body, and the medial occipital lobe. The inferior wall is formed by the horizontal part of the posterior perimesencephalic membrane, the medial wall by the midbrain tegmentum, the lateral wall by the medial occipital lobe, and the posteromedial wall by the ascending part of the posterior perimesencephalic membrane. The posterior ambient cistern communicates with the cerebellomesencephalic cistern inferiorly and the quadrigeminal cistern posteromedially. The ambient cistern contains the AChA, the P2 and P3 segments with their branches, the basal vein of Rosenthal, and, infrequently, a segment of the superior cerebellar artery.Cerebellomesencephalic cistern. The cistern is a wing-shaped infratenrorial compartment and enclosed by the cerebellar peduncle, the central lobule, the ala cerebella and dorsal midbrain. It can be divided into central and lateral compartments. The central compartment is located anteroinferiorly to the central lobule. Its anterior wall is formed by the lingual lobe and the posterior wall by the central lobule. It contains the trochlear nerve and some vessel branches, and communicates with the superior cerebellar cistern. The lateral compartment is positioned anteriorly to the ala cerebella. Its anterior wall is formed by the lower dorsal midbrain, the posterior wall by the ala cerebella, the superior wall by the horizontal part of the posterior perimesencephalic membrane, and the inferior wall by the superior cerebellar peduncle. It contains the superior cerebellar artery and the trochlear nerve. The compartment communicates with the posterior ambient cistern superiorly and the cerebellopontine cistern anteriorly.Quadrigeminal cistern. The quadrigeminal cistern is located inferior to the AEPG and contains five walls. Its superior wall is formed by AEPG, the anterior wall by the quadrigeminal plate medially and the medial pulvinar laterally, the posterior wall by the precentral cerebellar membrane, and the lateral wall by the ascending part of the posterior perimesencephalic membrane. The cistern contains medial posterior choroidal artery (MPChA) and some branches nourishing the dorsal midbrain. The MPChA perforates the ascending membrane, courses in the quadrigeminal cistern, and then passes through the gap between the medial pulvinar and the AEPG to enter the velum interpositum. The quadrigeminal cistern communicates with the posterior ambient cistern laterally, the superior cerebellar cistern posteriorly and the pericallosal cistern superiorly.Superior cerebellar cistern. The superior cerebellar cistern is positioned superior to the vermis and includes anterior and posterior parts. The anterior compartment is situated anterior to the central lobule. Its anterior wall is formed by the precentral cerebellar membrane and the inferior colliculus, the posterior wall by the central lobule, and the lateral wall by the posterior perimesencephalic membrane. It contains the superior vermian vein and some branches of the superior cerebellar artery. The anterior compartment communicates with the cerebellomesencephalic cistern inferiorly and the quadrigeminal cistern anteriorly. The posterior part is located above the culmen and clivas of cerebellum. Its superior wall is formed by the outer arachnoid membrane covering the cerebellum, and the inferior wall by the culmen and clivas. It contains the branches of the superior cerebellar artery. This compartment communicates with the cistern covering the upper the cerebellar hemisphere laterally and the cisterna magna posteriorly.ConclusionThe anatomy of the cisterns and its related arachnoid membranes in the perimesencephalic region has been reinvestigated in this study. Compared with previously reported studies, some new information was updated:1) The perimesencephalic membrane was identified as a set of inner arachnoid membranes surrounding the midbrain at the level of the tentorial incisura, it was an important membranous barrier between the supra- and infra-tentrial cisterns. Its formation and distribution were also been described in detail.2) The anterior tentorial edge was verified to be the lateral border of the mesencephalic membrane.3) The AEPG, including its formation, construction, content and relationship with adjacent arachniod membranes and structures, was illustrated systematically, which cannot been found in previous studies.4) The precentral cerebellar membrane has been identified and described in detail.5) The ambient cistern was verified, anatomically, to be a supratentorial cistern located above the level of the tentorial edge and perimesencephalic membrane.6) The borders and contents of the cisterns in the perimesencephalic region, as well as its relationship with adjacent cisterns have also been redefined.7) The arachnoid membranes may be one of the most important factors related to the growing pattern of the perimesencephalic tumors.8) A better understanding of the cisterns and membranes may be helpful to explore the morphologic features, design optimal surgical approaches and more precisely manage lesions in the perimesencephalic region.更多还原