摘要
研究背景及目的
桥小脑角区无论是出现功能性疾病(如三叉神经痛、面肌痉挛、舌咽神经痛)还是器质性疾病(听神经瘤),除了后颅窝神经、血管出现解剖变化外,桥小脑角区的膜性结构也相应的出现改变。但是不论它们的解剖关系如何变化,不同方式的微血管减压术(Microvascular decompression,MVD)大多时候主要是要将压迫膜性结构薄弱的颅神经上(尤其是颅神经进出脑干处)的责任血管隔离开来或是解除颅神经的压迫因素。即使是压迫因素远离REZ,也是要锐性分离、充分松解蛛网膜、神经鞘膜、系带等这些膜性结构和颅神经间的粘连,必要时甚至要剪断部分神经束带、鞘膜,以将贯穿入神经束内的责任血管推离开来。而听神经瘤终究是脑外肿瘤,与脑干、小脑、神经之间存在软脑膜、肿瘤表面的囊壁、神经鞘膜和蛛网膜相隔离,这给我们术中遵循膜性结构的层次和界面来进行听神经瘤手术提供了解剖基础。然这些膜性结构与神经和脑的解剖位置关系尚不清楚,至今存在广泛争议,病理情况下的膜性结构研究更是较少,值得进一步研究。
尽管越来越多的神经外科医生在处理三叉神经痛、面肌痉挛、舌咽神经痛患者时首选MVD,且绝大多数学者认为血管压迫症状源自包裹颅神经中枢段的膜性结构脱髓鞘变,文献报道也多在颅神经REZ处探查和减压,不同MVD方式也有不同程度的症状缓解。然而也存在其他微血管压迫部位的理论,减压方式也不同,也有不同程度的疗效,争论一直存在,原因不详。目前对MVD机制及其手术方式争议较大,缺乏统一标准,也缺乏解剖和膜性结构研究的依据。
临床上MVD减压方式各异,效果各不同,少数病例复发,甚至存在一些无效病例。尽管统计学上无显著性差异,但是复发和无效的原因不明,是否需要再次手术来处理和评估无效或是复发病例具有极大的挑战性,争论也较大。
临床上三叉神经痛和面肌痉挛患者到底责任血管压迫何处才产生症状?MVD减压的主要部位在何处?基础研究方面,减压处的颅神经显微解剖和膜性结构到底有何不同?其减压的理论和解剖学依据是什么等问题有待于研究解决,文献无这方面的解剖和膜性结构的系统研究。
一百多年来,听神经瘤起源是位于蛛网膜下腔之内还是位于蛛网膜下腔之外一直存在争议。听神经瘤手术时面、听神经之间的膜性结构关系的认识直接关系到听神经瘤手术显微操作的理念和术后面听神经功能保存率的高低。
然而近20年来,多数神经外科医生对面听神经术中解剖和术后功能的保存率水平都一直在较低范围内徘徊。对桥小脑角区膜性结构的研究对于促进临床上提高面听神经解剖和功能的保存具有重要的临床和理论价值,国内外尚无文献系统报道听神经瘤术中病理情况下的膜性结构的研究。
研究目的:
①与桥小脑角区病变有关的三叉、面听神经及其膜性结构的显微外科解剖和组织学研究,以了解三叉、面听神经中枢段、周围段、移行区域和内听道内面听神经池的膜性结构特点,为MVD减压部位及其手术方式和听神经瘤的神经起源提供解剖学依据;②与MVD有关的三叉神经痛、面肌痉挛的临床研究,探讨临床病例特点和术中所见及不同MVD术式治疗三叉神经痛、面肌痉挛的疗效比较,为改良MVD术式提供临床依据;③与听神经瘤有关的桥小脑角区膜性结构的临床研究,以探讨听神经瘤的起源,听神经瘤与膜性结构的解剖关系及对提高面听神经功能的保存的影响。
材料和方法
1实验部分材料与方法(与桥小脑角区病变有关的三叉、面听神经的显微外科解剖和组织学研究)
成人湿性头颅标本10例(20侧),6例男性,4例女性,死亡原因排除颅神经疾病,10%甲醛固定(南方医科大学解剖教研室提供)。所有标本两侧颈总、椎动脉灌注红色乳胶,静脉系统灌注蓝色乳胶。常规神经外科显微手术器械,自制头架,Zeiss NC4型手术显微镜(放大5～20倍),Cannon数码相机,高速气钻。圆规,游标卡尺(精确度0.02mm),光学显微镜。天狼猩红Van Gieson染色液(Sigma公司)。
1.1三叉、面神经、前庭蜗神经膜性结构的显微解剖学和组织学研究
成人湿性尸头标本10例(20侧),显微镜下解剖,完整取出并测量三叉神经感觉支、面神经运动支、前庭蜗神经脑池段长度。标本石蜡包埋,水平切片,天狼猩红苦味酸法染色。光学显微镜下测量三叉、面、前庭蜗神经中枢段与周围段的长度,分析它们之间组织学结构的不同。所有统计数据使用SPSS11.5软件包进行统计学处理,数据用(?)±s表示,以P＜0.05表示有显著性差异。三叉神经、面神经、前庭蜗神经三组颅神经中枢段长度测量结果比较,采用单向方差分析(One-way ANOVA)。在颅神经压迫症状必需是血管与颅神经有直接接触的这种假设前提下,根据已知的西方人三叉神经痛、面肌痉挛、舌咽神经痛的发病率与相应颅神经中枢段的长度进行双变量相关分析。
1.2面、前庭蜗神经脑池段的显微外科解剖学研究
模拟枕下乙状窦后入路,头架固定尸头,逐层解剖。先观察面、前庭蜗神经进出脑干端,桥小脑角段及其毗邻解剖关系。再自中心部将小脑半球切除,保护小脑外侧面蛛网膜结构的完整。观察小脑外侧面蛛网膜与内听道口之间的关系。自硬膜外磨除内听道上、后壁至内听道底部,平行于内听道切开硬膜,在显微镜下解剖观察面、前庭蜗神经脑池段,并进行数据测量和拍摄。统计20侧数据,经SPSS11.5统计软件计算样本均数和标准差,测量值范围以均数±标准差的形式表达。
2 MVD治疗面肌痉挛的临床资料与方法
按医生手术方式不同分为a、b组。a组常规微血管减压,患者30例,男性13例,女性17例;年龄35～67岁,平均50.5岁,病程8个月～7年,平均5年。b组全程围套式微血管减压,病例35例,男性15例,女性20例;年龄38～65岁,平均47.2岁,病程6个月～10年,平均4年。按患者起病时年龄分为c,d组,其中c组＜40岁27例,d组＞40岁38例。所有患者术前均接受过如药物、针灸或封闭等治疗。a组2例,b组4例患者术前在外院曾经接受面神经微血管减压术,效果不显著或短期缓解后复发。
回顾性分析两种微血管减压方式治疗65例面肌痉挛患者的术中情况、显微操作技术及结果。按手术方式不同分a组30例,b组35例。按起病时年龄分为c组＜40岁27例,d组＞40岁38例。所有统计数据使用SPSS11.5软件包进行统计学处理,以P＜0.05表示有显著性差异,不同面神经受压迫模式对比使用R×C列联表资料的卡方检验(Pearson Chi-square),不同手术组疗效采取两个独立样本的非参数检验,总的并发症发生率和复发率的比较使用列联表资料分析的四格表资料的卡方检验(Pearson Chi-square)。
3 MVD治疗原发性三叉神经痛的临床研究
3.1改良MVD治疗原发性三叉神经痛的临床资料与方法
87例患者中男性39例,女性48例,疼痛位于右侧54例、左侧33例。按疼痛始发年龄分为a组41例,平均年龄为64岁(60～75岁),病程8个月～13年,平均为7年;b组46例,平均年龄为47岁(30～59岁),病程9个月～10年,平均为3.5年。所有患者术前均经过药物、针灸、拔除下颌牙或封闭等治疗。a组3例,b组2例患者术前在外院曾经接受三叉神经微血管减压术,效果不显著或短期缓解后复发。a组2例患者曾在外院行射频、r刀治疗,疼痛无缓解。
回顾性分析改良MVD治疗87例TN的术中发现、显微操作技术及随访结果。所有统计数据使用SPSS11.5软件包进行统计学处理,以P＜0.05表示有显著性差异,两组总的并发症发生率的比较使用列联表资料分析的四格表资料的卡方检验(Pearson Chi-square)。
3.2静脉压迫性三叉神经痛的手术治疗临床资料与方法
33例患者中男性15例,女性18例;年龄30～75岁,平均55岁。病程8个月～13年,平均为5年。疼痛位于右侧20例、左侧13例。所有患者术前曾经过药物、针灸、拔除下颌牙或封闭等治疗。4例患者术前在外院曾经接受MVD,无效或短期缓解后复发。2例患者曾在外院行射频、r刀治疗,疼痛无缓解。其中25例(75%)患者为典型TN,5例(15%)不典型,3例(10%)表现为典型与不典型混合性。疼痛单独分布于三叉神经的第一、第二及第三支分别为3例、7例和4例。疼痛同时累及第二和第三支最常见,占11例(33.3%)。疼痛分布第一、第二支3例(10%),患者疼痛同时累及三个分支5例(14%)。
回顾性分析33例原发性三叉神经痛患者术中静脉压迫的处理及结果。对静脉压迫的处理采取细小静脉予以电凝阻断,岩上静脉复合体分支可部分阻断,保留主干;全程解剖分离血管压迫后予以Teflon围套式包裹三叉神经。
4与听神经瘤有关的桥小脑角区膜性结构及面听神经功能保存的临床研究临床资料与方法
63例均为我院收治并由同一组术者进行显微手术治疗的病例。其中男25例,女38例,年龄21～75岁,平均45.9岁。病程1个月至10年,平均2年6个月,左侧33例,右侧30例。1例为双侧听神经瘤,一侧肿瘤体积较小,听力尚存在;3例为外院术后复发的病例,其中1例第一次术后曾行r刀治疗。术前症状:听力存在2例,耳鸣、听力减退31例(49.2%),听力丧失30例(47.6%),眩晕32例(50.8%),声音嘶哑、饮水呛咳11例(17.5%),面部麻木33例(52.4%),重度面瘫2例(3.2%),中度面瘫5例(7.9%),轻度面瘫12例(19%),肢体共济障碍34例(53.9%),肢体力弱5例(7.9%)。头痛、视力下降12例(19%)。术前体征:第Ⅴ颅神经受累40例(63.5%),Ⅵ神经受累10例(15.9%),Ⅶ神经受累20例(31.7%),Ⅷ神经受累(听力障碍)61例(96.8%)。Ⅷ神经受累(前庭功能障碍):眩晕,走路不稳定,眼球震颤30例(47.6%),Ⅸ～Ⅺ神经受累10例(15.9%)。视乳头水肿6例(9.5%),小脑体征(共济失调)46例(73%)。锥体束征,一侧肢体病理征阳性6例(9.5%)。
根据影像资料及手术录像,回顾性分析我科近3年来经枕下乙状窦后入路显微手术治疗63例听神经瘤术中桥小脑区膜性结构与听神经瘤之间的解剖位置关系,手术前后面听神经功能情况;并将其中直径大于3.5cm的54例大型听神经瘤分为Ⅰ型(脑干腹侧型)、Ⅱ型(脑干小脑型)和Ⅲ型(嵌入型),对三种类型听神经瘤的手术方式、手术耗时进行回顾性分析。所有统计数据使用SPSS11.5软件包进行统计学处理,数据用(?)±s表示,以P＜0.05表示有显著性差异。不同分型患者肿瘤大小对比和不同类型的听神经瘤手术耗时使用单向方差分析(One-way ANOVA),多重比较使用SNK法。不同分型肿瘤术后面神经功能的对比采用Kruskal Wallis Test。
结果:
1.三叉、面神经、前庭蜗神经膜性结构的显微外科解剖学和组织学研究结果
三叉神经感觉支脑池段的长度为13.08±2.12(9.26～15.7)mm,中枢段长3.42±0.22(3.14～3.89)mm;面神经运动支脑池段(桥小脑角段+内听道段)长23.23±1.29(20.72～25.30)mm,中枢段长2.39±0.197(2.05～2.6)mm;前庭蜗神经脑池段长(桥小脑角段+内听道段)28.02±3.33(21.79～31.82)mm,中枢段长9.59±0.84(8.56～11.17)mm。三组颅神经中枢段特征性表现为圆锥形头端,推进周围段,中枢段神经轴索仅有薄层结缔组织膜包裹,周围段轴索排列疏松,结缔组织丰富。统计学分析三组颅神经中枢段长度有显著性差异(P=0.000),从长到短依次为:前庭蜗神经、三叉神经、面神经。西方人颅神经中枢段的长度与微血管压迫症状的发病率正相关(P=0.000)。
2.面、前庭蜗神经脑池段的显微外科解剖学研究结果
面、前庭蜗神经脑池段分为进出脑干段(root entry/exit zone,REZ)、桥小脑角段、内听道段。REZ有重要的解剖三角;桥小脑角段面神经运动支与前庭蜗神经走行关系恒定,走行在前庭蜗神经前上方,中间神经和面神经运动根在内听道中部融合成一支;桥小脑角池蛛网膜象袖套一样延续至内听道底部。
3.全程围套式与常规微血管减压术治疗面肌痉挛的对比研究结果
术中a、b两组均发现面神经受压迫有四种模式:单纯接触型,压迫型,黏连包绕型,无明确责任血管型;责任血管包括动脉、静脉、混合性,血管袢;c组术中多见蛛网膜增厚,d组多见血管的构筑改变而致血管解剖移位;出院时a组总有效率80%,随访24例,5例复发(20.8%)。b组总有效率97.1%,随访31例,1例复发(3.2%);并发症随访1年以上未恢复者a组:耳鸣、听力下降10%,共济失调6.7%,面瘫10%;b组:耳鸣、听力下降2.9%,面瘫2.9%。a、b两组血管压迫类型无显著性差异(P=0.856),b组总的有效率高于a组(P=0.019),b组复发率(P=0.038)和并发症(P=0.020)明显低于a组。
4.改良微血管减压术治疗原发性三叉神经痛结果
术中a、b两组三叉神经受压迫模式均有6种:单纯接触型,压迫型,黏连包绕型,无明确责任血管型,复杂型和贯穿型;责任血管包括动脉、静脉、混合性,血管袢。a组责任血管多位于三叉神经远外侧端,b组责任血管多位于三叉神经REZ;a、b组术后总有效率均为100%,无1例死亡。a、b两组术后总的并发症无显著差异(P=0.981),随访病例无复发,并发症随访1年以上均显著改善。
5.静脉压迫性三叉神经痛的手术治疗结果
静脉压迫可位于三叉神经整个脑池段;33例中22例既有静脉压迫也有动脉责任血管,11例责任血管为单纯静脉,其中3例为无名静脉,8例为靠近Meckel's腔的岩上静脉复合体;岩上静脉复合体按其引流模式分三种类型;微血管减压术后有效率为100%,平均随访2.5年无复发;术后主要并发症是三叉神经和小脑功能障碍,但经治疗后均明显改善。
6.与枕下乙状窦后入路听神经瘤手术有关的桥小脑角区膜性结构及其面听神经功能保存的临床研究
①听神经瘤远端未充满内听道底时有脑脊液信号;供血丰富的部分听神经瘤DSA显示存在椎动脉的分支供血;②术中发现听神经瘤基底可完全位于桥小脑角池,表面神经鞘膜形成囊壁,听神经瘤脑干侧、肿瘤本身和面听神经之间没有蛛网膜间隔。听神经瘤上、下极,背侧、腹侧面有蛛网膜覆盖。③本组肿瘤全切率为96.8%,面神经解剖保留率为85.5%,听神经解剖保留率为39.7%,本组无死亡。三组类型听神经瘤中嵌入型手术难度最大,耗时最长(P=0.000),但术后各型听神经瘤面神经功能的保存率无显著性差异(P=0.751)。
结论
1.①三叉、面神经周围段较中枢段因膜性结构不同而对血管压迫更具有抵抗性,中枢段容易出现血管压迫症状,MVD减压的部位主要为中枢段;②颅神经进出脑干端与移行区域是两个完全不同的部位,不可混用;③前庭蜗神经周围段可从内听道底延伸至桥小脑角区域脑池段。
2.①听神经瘤起源于蛛网膜下腔内,面、前庭蜗神经池与桥小脑池相连续;②听神经瘤可利用REZ解剖三角来寻找面、前庭蜗神经的起始段,并根据肿瘤生长方向不同与REZ的解剖关系分3种类型,有利于术中面、前庭蜗神经功能的保留;③磨除内听道后唇不能超过1cm,以免进入骨迷路。
3.全程围套式减压术治疗面肌痉挛更安全、有效;全程解剖分离面神经白REZ至内听道口,识别责任血管和可疑被压迫部位,置入Teflon棉对面神脑池段全程围套式包裹,避免损伤颅神经和细小穿支血管是影响疗效和减少复发的关键。
4.改良MVD治疗TN术后复发率低、安全,对老年人同样适用。全程解剖探查三叉神经痛脑池段,充分显露三叉神经REZ,识别责任血管和可疑被压迫部位并予以妥善处理,置入Teflon棉是提高疗效和减少术后复发及并发症的关键。
5.岩上静脉复合体是三叉神经痛最常见的责任静脉,静脉压迫无论是主要还是次要压迫因素时,均需要妥善处理,对三叉神经充分有效减压。微血管减压术避免了遗漏静脉压迫,减少了复发,但术后并发症稍偏高。
6.①听神经瘤位于蛛网膜下腔内,肿瘤脑干侧以及肿瘤本身和面听神经之间没有蛛网膜间隔。肿瘤上、下极,背侧、腹侧面覆盖的蛛网膜是桥小脑角池固有的蛛网膜,沿蛛网膜层或肿瘤囊壁界面将肿瘤与面听神经、脑干分离开来有助于提高全切率和面听神经功能的保存;②熟悉桥小脑角区膜性结构解剖,根据肿瘤与脑桥、小脑的位置关系分型,采取相应的手术策略,有助于提高手术效果。
Background and purposes of the research
Regardless of functional diseases in the cerebellopontine angle zone such as trigeminal neuralgia (TN),hemifacial spasm (HFS),and glossopharyngeal neuralgia (GPN),or parenchymal diseases such as vestibular schwannoma,the cerebellopontine angle zone meningeal layers will result in anatomical variations respective with the nerves and vessels of posterior fossa. However, the key steps for different modes of MVD techniques are to identify arteries or veins compressing a cranial nerve where the nerve sheath are thinner(especially the root entry/exit zone,REZ),neurovascular conflict,the doubted compression places which should be appropriately separated away. Even though compressive factors involved the distal segment of the nerve part from the REZ. Adhesions betweed the arachnoid membrane,nerve sheath,fraenulum and the involved nerve shoul be separated away. Some nerve tracts and fraenulum had to be interrupted when it was in need in order to push the offending vessels which penetrated intrafascicular away.
Vestibular schwannomas originate outside brain. There are pia mater,capsule wall of tumor consisted of vestibular nerve sheath, arachnoid membrane layers covered posterior nerves and brain surface,neurilemmal sheath between the brain stem,cerebellum and the tumor. The cerebellopontine angle zone meningeal layers offer anatomy foundations to remove vestibular schwannomas following with neuroma/ nerve interface. However,the anatomical variations of meningeal layers with vasculonervous structures and neuromas are still unclear or inaccurate with unresolved controversies.
More and more neurosurgeons widely offer MVD to treat trigeminal neuralgia (TN),hemifacial spasm (HFS),and glossopharyngeal neuralgia (GPN) patients for the first choice,many MVD modes have some low or high probability of remaining symptomatic relief that late recurrences have also been reported. However,in line with the variety of different theories regarding the site or sites of vascular compression that cause syndrome,there is wide variation in the types of decompression techniques that neurosurgeons recommend. Different MVD modes have more controversies surrounding the issues of the standard mode,the pathogenesis of microvascular decompression (MVD) without insufficient systematic anatomic and histology study to be based on. Although different MVD modes with different techniques resulted in curative effect in variation,MVD is an efficacious method to treat TN,HFS,GPN with good outcomes. Such a high degree of surgical success makes a statistically significant analysis difficult of the very small subset of recurrent,inefficient patients .The exact reasons for surgical failure or recurrence remain unclear. It is debatable for the postoperative evaluation and management of failure or recurrence and present a challenging decision regarding whether a second surgical procedure should be performed. There is no consensus among neurosurgeons regarding which site or sites of compression actually cause this condition,and,thus,which should be operated on to provide relief. Many etiological theories have been proposed,but none have yet been definitively proven.
There is no consensus among neurosurgeons regarding which site or sites of compression actually cause trigeminal neuralgia,facial spasm,which should be operated on to provide relief. What different variations based on surgical anatomic and histological features are about decompression site of the nerve. What the theoretical and anatomic evidences are about MVD,et al. All these are waiting for being resolved. So far there have been rare system reports on anatomy and histological evidence of MVD and decompression site.
It has been debatable for more than one hundred years to accept that the origin of an vestibular schwannomas is located outside or inside the subarachnoid space. The origin concept of acoustic neuroma which should be paid particular attention to the arachnoidal membrane during surgical procedures is important to remove tumor with low or high probability of preservation of facial and vestibulocochlear nerves.
However, in the late two decades, anatomical and functional preservation rate of facial and hearing nerves is still kept in low scope. The study of cerebellopontine angle zone meningeal layers aims to improve anatomical and functional preservation of hearing and facial nerves related to vestibular schwannoma surgery via the retrosigmoid approach. It will bring immportant theoretical and clinical values for the study. So far there have been rare system reports on the study of intraoperative cerebellopontine angle zone meningeal layers related to vestibular schwannoma surgery via the retrosigmoid approach.
The purposes of the research are①to study microanatomy and histology of trigeminal,facial and vestibulocochlear nerves,cerebellopontine angle zone meningeal layers and explore the microanatomy and histology of the central nervous system segment (CNS),peripheral nervous system(PNS) segment and transition zone(TZ) in trigeminal and vestibulocochlear nerves,acousticofacial cistern from cadavers so as to offer anatomic references for microvascular decompression and origin of an vestibular schwannomas.②To the different MVD modes for idiopathic trigeminal neuralgia,facial spasm and explore the efficacy differences and surgical techniques,findings and outcomes avoiding of recurrence to find clinical evidences for modified MVD.③To study the origin of vestibular schwannomas and effect of cerebellopontine angle(CPA) zone meningeal layers anatomy variation on the surgical technique for removal of vestibular schwannoma with improved preservation of hearing and facial nerve function.
Materials and Methods
Experiment data
1. Histological and micranatomy study on the membranes structure of the central nervous system segment,peripheral nervous system segment and transition zone in the trigeminal,facial and vestibulocochlear nerves
The cisternal portions of the trigeminal nerve and the acousticofacial nerves were removed enbloc for observation and measurement with micro-operative techniques in 20 sides from 10 cadaveric heads. Each tissue was fixed in formalin and then embedded in paraffin and sectioned horizontally with the aid of scarlet nitroxanthic acid staining method. Specimens were light microscopically measured the length of CNS,PNS,TZ segments and analyzed for structural differences between the CNS and PNS segments. The statistical analysis was performed with SPSS11.5 software package and the data were presented with(Mean±Standard Deviation). The differences between the length of CNS among trigeminal,hemifacial,and vestibulocochlear nerves were analyzed with One-way ANOVA,being significant when P<0.05.If vascular contact with the CNS segment of a cranial nerve is necessary to cause symptoms,we analyzed the correlation of the known incidences of trigeminal neuralgia,hemifacial spasm,and glossopharyngeal neuralgia in the west are related to the length of their respective CNS segments through double-variance correlationship analysis.
2.Microsurgical anatomy of cisternal segments of facial and vestibulocochlear nerves
The anatomic relationships and datas of facial and vestibulocochlear nerves were observed and measured using microscope in 5 to 20xmagnification with microsurgical techniques through retrosigmoid approach in 20 sides from 10 formalin-fixed and perfused cadaveric heads with color silicon.
Clinical data
3. Microvascular decompression with whole range encircling mode versus conventional microvascular decompression in treatment of hemifacial spasm
We retrospectively analyzed the collected datas of all patients with the diagnosis of hemifacial spasm from January 1998 to January 2006. Intraoperative findings,surgical technique,and outcomes were recorded. The patients were divided into Group a (30 cases) and Group b (35 cases) according to different operative modes, Group c (below 40yr) and Group d (above 40yr) according to the onset age of symptom. The statistical analysis was performed with SPSS11.5 software package. Overall effective rate of group a and b were analyzed with 2 independent sample nonparametric test,being significant when P<0.05. The differences between four facial nerve compression categories, total complicated and recurrent incidences in two groups were analyzed with Pearson Chi-square,being significant when P<0.05.
4. Modified microvascular decompression for idiopathic trigeminal neuralgia
We retrospectively assessed surgical technique,findings and outcomes in 87 patients who underwent modified MVD. The outcomes from 41 consecutive patients with a mean age of 64 years(range,60～75yr) were compared with those from 46 younger group(mean age,47yr;range,20～59yr) operated on during the same period. The statistical analysis was performed with SPSS11.5 software package. The differences between the complication incidence,the mean length of hospital stay and pain relief in group a and group b were analyzed with Pearson Chi-square,being significant when P<0.05.
5. Surgical treatment for idiopathic trigeminal neuralgia caused by venous compression
Surgical management technique and outcomes in 33 patients were retrospectively analyzed. Tiny veins were coagulated and cut,the offending vein was coagulated and cut when the vein was one of several superior petrosal veins complex(SPVC).However,the vein was preserved,divided away from the nerve and not cut in cases in which it was a large main drainer. After exposure of the entire cisternal trigeminal nerve,teflon graft was properly interpositioned to encircle the whole range of it.
6. Study of cerebellopontine angle zone meningeal layers and preservation of hearing and facial nerve function related to vestibular schwannoma surgery via the retrosigmoid approach
63 patients with vestibular schwannoma in our department during the last 3 years were divided into three groups on the basis of radiological features and operative record. The clinical features, microsurgical technique and results were analyzed retrospectively. The micranatomical position relationship between the cerebellopontine angle zone meningeal layers and tumor,hearing and facial nerve function were analyzed retrospectively for 63 patients with vestibular schwannoma via the retrosigmoid approach in our department during the last 3 years. 54 large tumors in a series of 63 patients were divided into three groups(Ventral brainstem group, Brainstem-cerebellum group and Incuneation group)on the basis of tumor exceeding 3.5cm in size. Surgical technique and operative duration on these three groups were analyzed retrospectively. The statistical analysis was performed with SPSS11.5 software package and the data were presented with(Mean±Standard Deviation). Statistical significance was set at P<0.05.The differences between the large tumor size and operative duration in three groups were analyzed with One-way ANOVA. Comparisons of postoperative facial nerve functions between the 3 groups were performed using Kruskal Wallis Test.
Results
1. Microscopic measurement demonstrate that the cisternal portions of trigeminal, hemifacial,and vestibulocochlear nerves respective were 13.08±2.12(9.26～15.7)mm,23.23±1.29(20.72～25.30)mm,28.02±3.33(21.79～31.82)mm.The histological examination revealed that the CNS segment of trigeminal,hemifacial, and vestibulocochlear nerves respective were 3.42±0.22(3.14～3.89)mm,2.39± 0.197(2.05～2.6) mm,9.59±0.84 (8.56～11.17) mm.The cone-like organizationobserved at the top of the CNS segment was characteristic. It pushed into the PNSregion,which surrounded the CNS segment. The PNS region revealed a parallel-aligned organization of the axons,which was loosely arranged to be rich inconnective tissue.The CNS segment was surrounded by thinner connective tissue,but to a far lesser extent than in the PNS segment. The length of the CNS segmentof vestibulocochlear nerve is longer than the CNS segment of the trigeminal nerve,which is longer than the CNS segment of the facial nerve(P=0.000).We found aclear epidemiological correlation between the length of the CNS segment, whichdiffered among cranial nerves, and the incidence of the microvascularcompression syndrome in the west(P=0.000).
2.The cisternal segments of facial and vestibulocochlear nerves were divided into three segments,namely,REZ,cerebellopontine angle, internal acoustic meatus(IAM) segment. There was an important anatomical triangle in the area of REZ.The facial nerve motor root of cerebellopontine angle segment exposed a regular relation with the vestibulocochlear nerve in their pathways. The motor root had its location in the anterior-superior vestibulocochlear nerve and converged into one with the intermediate nerve in the middle of IAM. The arachnoid membrane of cerebellopontine cistern invaginated into the fundus of IAM as a muff.
3. Results of MVD for facial spasm
We ascertained the facial nerve intraoperative compressed by degree was classified into 4 categories: Single contact,Contact and indentation, Adhesion and encasement,No identified offending vessels type.The offending vessels included arteries,veins,vascular loops. In the most patients of Group c,arachnoid membrane around the facial nerve was thick and encased the offending vessel;In Group d,the characteristic changes of the vasculature were the offending artery,which compressed the facial nerve was elongated,redundant,and focal arteriosclerosis. In Group a,the overall effective rate was 80%, the recurrent rate was 20.8%.In Group b,the overall effective rate was 97.1%,the recurrent rate was 3.2%.The chief permanent complications were hearing impairment found in 10.0% and ataxia in 6.7% of patients in Group a. In Group b,the rate of hearing impairment was 2.9 %,ataxia was 2.9%.There was no significant difference in terms of four facial nerve compression categories(P=0.856).Overall effective rate in group b was significantly higher than that of group a(P=0.019),however,the complicated incidence(P=0.020),recurrent incidence(P=0.038) in Group a were significantly higher than that of Group b.
4. Results of modified MVD for idiopathic trigeminal neuralgia
The trigeminal nerve compressed by mode was classified into 6 types:Single contact,Contact and indentation,Adhesion and encasement,No identified offending vessels,Transfixation and Complicated type. The offending vessels include arteries,veins,vascular loops. Location of the neurovascular conflict was often in the midthird and distal segment of the trigeminal nerve in Group a and at the trigeminal root entry/exit zone in Group b.Pain relief achieved 100% in 87 cases. In our series of modified MVD procedures,there was no significant difference in terms of postoperative complications between two groups (P=0.981).There were no operative mortalities or life-threatening morbidities. After average follow-ups of 2.5yr,no case recurred. The complications improved after discharge through treatments.
5.Results of surgical treatment for idiopathic trigeminal neuralgia caused by venous compression
Location of the neuroveins conflict can be at all along the cisternal trigeminal nerve. The venous conflict was associated with one (or several) offending artery(ies) in 22 cases. The venous compression was pure in 11(12.6%), among 3 was unnamed vein while,8 was SPVC near Meckel's cave. The patterns of drainage of the SPVC were classified into three groups. Complete pain relief in all patients after microvascular decompression. After mean follow-ups of 2.5yr,no case recurred. Four patients developed trigeminal nerve impairment and 2 cases suffered from disordered cerebellum function, which improved through treatment.
6.Results of Study of cerebellopontine angle zone meningeal layers and preservation of hearing and facial nerve function related to vestibular schwannoma surgery via the retrosigmoid approach
①Cerebrospinal fluid emerged between the distal portion of vestibular schwannoma and the fundus of auditory meatus. DSA showed the some vestibular schwannomas with abundant blood supply on MRI examination was fed by the branch(es) of vertebral or basilar artery.②the vestibular schwannoma base can wholly locate in CPA cistern. The capsule wall of tumor consisted of vestibular nerve sheath. Arachnoid membrane layers covered posterior and ventral surface, superior and inferior poles of tumor,no arachnoid membrane interface was present between tumor and facial,vestibulocochlear nerves,also at side opposite to brainstem.③)Total tumor removal was accomplished in 96.8% of the patients. Anatomical preservation of the facial nerve and the cochlear nerve were achieved in 85.5% and 39.7%,respectively. There was no death in this group. The resection of groupⅢtumor with the longest time-consuming was the most difficult (P=0.000).However,it is not significant different from three groups for preservation of facial nerve function(P=0.751).
Conclusions
1.①Histological differences between the PNS and CNS segments suggest that the PNS segment is more resistant to compression. The evidence we present supports that vascular compression syndromes prone to arise from vascular contact along the CNS segment of the cranial nerves.②The data definitively prove that the root entry zone (REZ, nerve-pons junction) and TZ of the nerves are distinct sites and that these terms should never be used interchangeably.③The peripheral nervous system segment in the vestibulocochlear nerves could extend from cerebellopontine angle cistern to the fundus of internal acoustic meatus.
2.①The origin of acoustic neuroma was inside the subarachnoid space,the cousticofacial cistern was a lateral extension of the cerebellopontine cistern.②The initial segments of facial and vestibulocochlear nerves can be located according to REZ anatomical triangle.The acoustic neuroma can be classified 3 types according to different tumor growth directions and anatomic relationships with REZ anatomical triangle. The functions preservation of facial and vestibulocochlear nerves can benefit from the categories.③To avoid entering the labyrinth,the bone exposure of IAM does not extend to the lateral end about 1cm.
3. The report demonstrated that microvascular decompression with whole range encircling mode was more safety associated with higher cure rate. The key steps were to expose the entire facial nerve from the pons to internal auditory canal to identify neurovascular conflict,especially the REZ,the doubted compression places which should be appropriately separated away. Teflon graft was properly interpositioned to encircle the cisternal portion of facial nerve. Fewer disturbance to cranial nerves avoiding injury to the penetrating vessels from REZ and the pons were essential to improve the efficacy,reduce recurrence and complications.
4.The report demonstrated modified MVD was safe and higher effective without recurrence. It was also suitable for the elderly. The key steps were to expose the entire trigeminal nerve from Meckel's cave to pons to identify neurovascular conflict,especially the REZ,the doubted compression places which should be appropriately separated away. Teflon graft was properly interpositioned to encircle the whole range of trigeminal nerve. All these done are essential to improve the efficacy,reduce recurrence and complications.
5.SPVC is most frequently the offending vein. Whether the venous compression was main compressing factor or not,it was essential to deal with them and adjust surgical strategy. The trigeminal nerve was completely decompressed from veins followed with or without arterial compression in all patients. MVD may identify the venous compression accurately and reduce the recurrence. However,it could result in higher postoperative complications.
6.①Vestibular schwannoma locates inside of arachnoid membrane layers. Arachnoid membrane layers covering tumor is intrinsic extension of cerebellopontine cistern. Arachnoid membrane layers covered posterior and ventral surface,superior and inferior poles of tumor,no arachnoid membrane interface was present between tumor and facial,vestibulocochlear nerves,also at side opposite to brainstem. Intraoperative difficulties in total tumor removal and preservation of hearing and facial nerve function can be avoided in atraumatic dissection and separation between the duplication of arachnoidal layers or cyst wall of tumor.?Surgical results of large vestibular schwannoma can be improved by familiarity with the anatomy of cerebellopontine angle zone meningeal layers and adoption of corresponding surgical strategy according to its anatomical relationship to brain stem and cerebellum.
引文
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