Anatomical basis for the lateral approach to the fourth ventricle

Abstract

This study focused on the posterior inferior cerebellar artery bifurcation and branching patterns in the fissures around the fourth ventricle. The vertebral arteries in 25 unfixed human cerebellum were cannulated and injected with polyester colored resin. The suboccipital surface of the cerebellum was exposed and the cisterna magna main landmarks localized. The average distance was 12.6 mm between the tonsillovermlan notches and 21.8 mm between the inferior tips of the tonsils. The mean vertical distance between these horizontal planes was 14.5 mm. The posterior inferior cerebellar artery was found in the cerebellomedullary fissure in 42 of 50 cerebellar hemispheres, in seven cases the artery was absent and in one it was hypoplastic. The mean outer diameter was 1.8 mm and the average length was 27.9 mm. The posterior inferior cerebellar artery presented four bifurcation point patterns: superomedial, superolateral, inferomedial, and inferolateral. These patterns were characterized into subtypes based on the courses of the vermian and tonsillohemispheric branches. The perforating and choroidal branches originating in these segments were also studied. The mean number of perforating branches per hemisphere was 5.1. The range of the length was 2-10 mm and the range of the outer diameter was 0.1-0.3 mm. An average of 4.6 choroidal arteries originated from the tonsillomedullary and telovelotonsillar segments, a mean of 4 arose from both vermian and tonsillohemispheric branches. This information will facilitate surgical planning in approaching the fourth ventricle as well as the interpretation of cerebellar infarcts in the posterior inferior cerebellar artery area. [Neurol Res 1999; 21: 444–456]     

Microsurgical anatomy of the posterior circulation

CONTEXT: The microsurgical anatomy of the posterior circulation is very complex and variable. Surgical approaches to this area are considered risky due to the presence of the various important blood vessels and neural structures. AIMS: To document the microsurgical anatomy of the posterior circulation along with variations in the Indian population. MATERIALS AND METHODS: The authors studied 25 cadaveric brain specimens. Microsurgical dissection was carried out from the vertebral arteries to the basilar artery and its branches, the basilar artery bifurcation, posterior cerebral artery and its various branches. Measurements of the outer diameters of the vertebral artery, basilar artery and posterior cerebral artery and their lengths were taken. RESULTS: The mean diameter of the vertebral artery was 3.4 mm on the left and 2.9 mm on the right. The diameter of the basilar artery varied from 3-7 mm (mean of 4.3 mm). The length varied from 24-35 mm (mean of 24.9 mm). The basilar artery gave off paramedian and circumferential perforating arteries. The origin of the anterior inferior cerebellar artery (AICA) varied from 0-21 mm (mean 10.0 mm) from the vertebrobasilar junction. The diameter of the AICA varied from being hypoplastic i.e., CONCLUSIONS: The authors have documented the various anomalies as well as the differences of the anatomy in this area in the Indian population as compared to the Western literature.     

Microsurgical anatomy of the posterior choroidal arteries

Abstract

In this study; we analysed the microanatomy of the medial and lateral posterior choroidal arteries, which supply vital central nervous system structures to the brainstem and choroids plexus. We traced the anatomical course of the medial and lateral posterior choroid arteries, their origin, diameter, number of branches, length, and anatomical variations. Twenty-six human unfixed brains were injected through the vertebral and carotid arteries with silicon rubber. Fifty-one out of a total of 129 vessels were medial posterior, and 78 were lateral posterior choroidal arteries. We divided the medial posterior choroidal artery into three segments: around the brainstem, quadrigeminal-pineal, and choroidal. The mean length of the medial posterior choroidal artery was 77.6 + 15 mm on the right side, and 77.1 ±15 mm on the left; the mean outer diameter observed was 0.8 ±0.5 mm on the right side, and 0.8 ±0.4 mm on the left. The number of branches arising from the medial posterior choroidal arteries averaged 25±9. In the lateral posterior group, the mean length observed was 49.5±26 mm on the right, and 58.0 ±23 mm on the left. There were instances of duplication and triplication of the lateral posterior choroidal vessels. The outer diameter averaged 0.72 mm on the right, and 0.6 mm on the left. The posterior choroidal arteries are clearly an important vascular component. A comprehensive knowledge of their anatomy will aid the neurosurgeon during surgery of the brainstem, pineal region, and third ventricle, and will limit complications resulting from injury to these arteries. [Neurol Res 1995; 17: 334-344]     

Microsurgical anatomy of the anterior choroidal artery

Microdissection of 100 hemispheres from human cadavers were performed in order to study the anatomic characteristics of the anterior choroidal artery (AChA). One AChA per hemisphere was found. In 98% of hemispheres the AChA arose from the internal carotid artery (ACI) 2.4mm distal to the origin of the posterior communicating artery (ACoP) and 4.7mm proximal to the carotid bifurcation. One or more perforating branches arose from communicating segment of ACI in 29% of hemispheres. The average calibre of the cisternal portion was 0.9mm and the plexal portion 0.7mm. The most frequent branches of the cisternal portion pass to the optic tract, cerebral peduncle, uncus and lateral geniculate body. Anastomosis were found between branches of the AChA and posterior cerebral artery, ACoP, middle cerebral artery and ACI. The results are discussed.     

远外侧入路手术中椎动脉颅内段的显微解剖应用研究

目的 对椎动脉颅内段进行观察和测量,探讨远外侧人路手术中如何保护椎动脉颅内段和小脑后下动脉. 方法 手术显微镜下对20例带颈成人头颅标本模拟远外侧人路开颅,到达颈静脉孔区,显露椎动脉颅内段及其主要分支,观察其走形特点和形态,并测量相关数据. 结果椎动脉颅内段穿寰枕筋膜后在基底动脉沟与对侧椎动脉合成基底动脉.椎动脉与舌下神经关系密切,本组30侧椎动脉穿经舌下神经根的腹侧达桥脑延髓沟,8侧椎动脉穿舌下神经根丝之间,2侧椎动脉经舌下神经根丝的背侧.70%的椎动脉与舌下神经有接触,其中30%的椎动脉对舌下神经造成压迫.椎动脉颅内段主要分支有小脑后下动脉、脊髓前动脉、脑膜后动脉和一些穿动脉.小脑后下动脉是椎动脉最大的分支,本组全部发自椎动脉颅内段,行程多为袢状并同后组颅神经关系密切.小脑后下动脉的起始点因人而异,同一标本左右也不一致,大多起自椎动脉颅内段的中上1/3.本组未见小脑前下动脉起源于椎动脉.脊髓前动脉均起于双侧椎动脉的末段,在中线吻合成一单干,沿脊髓前正中裂迂曲下降供应脊髓. 结论 熟悉椎动脉颅内段及其分支的走形特点和解剖变异有助于远外侧入路到颈静脉孔区手术中识别和保护椎动脉颅内段的主要分支.     

Anastomoses among the perforating arteries of the brain. Microanatomy and clinical significance

Anastomoses among the perforating arteries were examined in 50 human brains using injection technique with India ink and gelation, or methylmethacrylate. Anastomoses were not found among the perforators of the internal carotid artery and the thalamogeniculate branches. Anastomotic channels involving perforating branches of the anterior choroidal, middle cerebral, and anterior cerebral arteries were noted in 1% of the cases. Vascular connections of the premamillary arteries were observed in 30% of the brains. They varied from 60 to 280 microns) in diameter, and from 0.3 to 3.6 (mean 1.5 mm) in length. Anastomoses among the interpeduncular (thalamoperforating) branches of the posterior cerebral artery were present in 79% of the cases. They ranged from 80 to 400 microns (mean 146 microns) in caliber, and from 0.9 to 6.1 mm (mean 3.3 mm) in length. Since anastomoses among the interpeduncular and the premamillary arteries are much more frequent than those among other perforators, thalamic, subthalamic, and midbrain's infarctions seem to be less frequent than capsular and ganglionic ischemic lesions.     

Aneurysm of the posterior inferior cerebellar arteries/communicating artery

Only 3 cases of aneurysm associated with the communicating artery between both distal posterior inferior cerebellar arteries (PICAs) have been reported in the literature. We present the 4th case of such an aneurysm arising from the communicating artery itself, which is unrelated to the arterial branches. A hypertensive 68-year-old man presented with a Hunt and Hess grade 4 subarachnoid hemorrhage. Angiographic studies revealed that the ruptured aneurysm arose from the fine communicating artery itself interconnecting both distal PICA vermian branches. The right PICA was absent and its vermian territory was supplied by the left PICA through this communicating artery. At surgery, a saccular aneurysm was noted which developed at the top of the arterial loop under the nodulus of the cerebellar vermis and was trapped. The actual prevalence and clinical significance of aneurism associated with the communicating artery interconnecting both PICAs are unknown, but defective embryonal development may lead to congenital vulnerability of the vascular wall, resulting in aneurysm formation.     

与中枢性尿崩症相关的穿动脉显微外科解剖

目的 探讨下丘脑、垂体柄和神经垂体的穿动脉的显微解剖，为减少术后中枢性尿崩症提供解剖学依据。方法 借助手术显微镜观察20例成人尸头标本的第三脑室前部、垂体柄和神经垂体的穿动脉的显微解剖关系。结果 室旁核和视上核的血供来自于前交通动脉的穿支，该区域自外下部的血供主要来自后交通动脉的穿支；垂体柄的血供来自于垂体上动脉；神经垂体的血供来自垂体下动脉。结论 与中枢性尿崩症相关的穿动脉可分为3组：（1）前组：主要来自前交通动脉附近发出的穿动脉；（2）外侧组：来自颈内动脉床突上段和后交通动脉发出的穿动脉；（3）下组：发自颈内动脉海绵窦段的垂体下动脉。了解这些血管的分布，可减少在鞍区肿瘤手术时对这些血管的损伤，避免中枢性尿崩症的发生。     

The perforating branches of the P1 segment of the posterior cerebral artery

The perforating branches of the P1 segment of the posterior cerebral artery are vulnerable to injury. Because of their close proximity to the basilar artery, the vulnerability occurs especially during surgical interventions for vascular pathologies such as basilar apex aneurysms. Therefore, extensive knowledge of the microsurgical anatomy of this area is mandatory to prevent poor post-operative outcomes. We microscopically examined 28 P1 segments obtained from 14 adult fresh cadaver brains (6 silicone injected, 8 freshly examined). The P1 segments ranged between 2.8 mm and 12.2 mm (mean 6.8 mm) in length with a mean outer diameter of 1.85 mm (range 0.8–4.5 mm). All 94 thalamoperforating branches identified in 27 P1 segments (mean 3.35 branches per segment) arose from the postero-superior aspect of P1 and were the most proximally originating branch in nearly all specimens (96.4%). In addition in 28 P1s, 12 short circumflex arteries (42.8%; mean 0.42 branches per segment), 16 long circumflex arteries (57.1%; mean 0.57 branches per segment) and 10 medial posterior choroidal arteries (35.7%; mean 0.35 branches per segment) were identified and all originated from the posterior or postero-inferior surface of the P1 segment. When the P1 segment had more than one type of branch, it was the short circumflex arteries that were always more proximal in origin than the others. The medial posterior choroidal arteries were always more distal in origin. All three branches were not observed together in any of the P1 segments. The findings in this, and future, anatomical studies may help to reduce the post-surgical morbidity and mortality rates after surgery for posterior circulation aneurysms.     

小脑浅静脉的显微解剖及临床意义

目的 观察小脑浅静脉的显微解剖结构.方法 利用20具(40侧)尸头标本,动、静脉分别用红蓝色乳胶灌注,在显微镜下观察小脑浅静脉的构成并测量相关的数据.结果 小脑浅静脉的构成中,15具标本的小脑中央前静脉纤细,外径平均为(1.1±0.14)mm;5具标本粗大,外径平均为(2.0±0.20)mm.20具标本(40侧)小脑前...     

前交通动脉复合体的解剖学研究

目的通过在手术显微镜下对鞍区前交通动脉复合体及各自发出的穿支动脉的解剖和测量,进一步掌握和熟悉前交通动脉复合体的结构及毗邻血管神经的走行,为手术入路提供参考。方法在30侧(15例)福尔马林固定的成人湿性头颅标本上,模拟双侧翼点入路开颅,对鞍区前交通动脉复合体及各自发出的穿支动脉进行解剖观察和测量,所得结果用SPSS 10.0软件进行统计分析。结果描述和测量了前交通动脉复合体及其各分支、穿通动脉和神经的毗邻、走行及直径、长度。ACA均由前穿支下方的ICA发出对侧大脑前动脉借前交通动脉相接。回返动脉为ACA-A1段发出的穿动脉中最粗大的血管,起源部位、行程及数量变异大。ACoA的形态与双侧A1段直径关系密切。结论间隙Ⅱ中回返动脉起点范围通常位于前交通动脉近侧3 mm及前交通动脉远侧3 mm范围内,故在前交通动脉水平远、近侧3 mm范围内临时夹闭或解剖ACA时,易造成回返动脉损伤。在A1段近侧3~5 mm、A1段中1/3段少有穿支发出,此二处可作为ACoA动脉瘤手术时临时阻断的部位,而A1段远侧、特别在ACoA水平2 mm附近几乎均有回返动脉平行伴行,在此处解剖极易损伤回返动脉。A1段发育不全与ACoA动脉瘤可能有较高的相关性。     

Microsurgical anatomy of the intracranial part of the vertebral artery

Abstract

We studied the intracranial portion of the vertebral artery and its branches in 11 cadaveric specimens. We evaluated the course of vessels and their dimensions (external diameter and length), as well as relationships between each of them. The vertebral artery was larger on the ? left side in two cases, on the right in five cases, and equal on both sides in four cases. The right and left vertebral arteries joined each other forming the basilar artery at the level of the pontomedullary junction in four cases, 2 mm below it in one case, and 1 to 7 mm above it in six cases. We divided all branches of the intracranial vertebral artery into two groups: the medial branches and the lateral branches. Two major types of medial branches were observed: the anterior spinal artery and the branches of the foramen caecum. The origin of the anterior spinal artery was located 6.5 mm (5-11 mm) proximal to vertebrobasilar junction on the right and 8.5 mm (6-17 mm) on the left. The anterior spinal artery was absent on the right in two cases and on the left in one. Branches arising from the vertebral artery to the foremen caecum were found in four brains. Lateral branches originated from the posterolateral or lateral aspect of vertebral artery. The posterior inferior cerebellar artery, the largest branch of the vertebral artery, was included in this group. Other branches were mostly located between the origin of the posterior inferior cerebellar artery and the vertebrobasilar junction. Forty-six lateral branches originating from the vertebral artery were found in 11 brains (26 on the right and 20 on the left). Lateral branches widely anastomosed with perforators from the basilar arteryposterior inferior cerebral artery; and the anterior inferior cerebellar artery. [Neurol Res 1994; 16:171–180]     

Dissecting aneurysms of the posterior inferior cerebellar artery: report of four cases and review of the literature

Dissecting aneurysms frequently involve the vertebral arteries and their branches, but those exclusively on the posterior inferior cerebellar artery (PICA) represent only 24 cases in the literature, including the four cases discussed in this article. The clinical diagnosis lacks pathognomonic signs or symptoms, with presentations such as subarachnoid haemorrhage or ischaemia of the brain stem or the cerebellum, and the management is controversial. Wrapping, clipping and embolisation of the aneurysms were tried in this series with different outcomes. Exclusion of the pathological segment should be performed, as shown by rebleeding from our case which was wrapped or by progression of the vascular disease in cases where treatment was delayed. Surgical or endovascular occlusion are well tolerated in our cases and in those reported from the literature, which implies the absence of normal perforating branches to the brain stem arising from the proximal dissected segment of the PICA and a good collateral circulation. A revascularisation procedure using the occipital artery can be performed in order to prevent infarction if an endovascular test occlusion is not tolerated.     

Perforating branches from offending arteries in hemifacial spasm: anatomical correlation with vertebrobasilar configuration

OBJECTIVE: In microvascular decompression for hemifacial spasm, the perforating branches around the facial nerve root exit zone occasionally complicate facial nerve decompression. In this context, the vertebrobasilar configuration was retrospectively correlated with the perforating branches. METHODS: Based on vertebral angiography, magnetic resonance angiography, and three dimensional computed tomographic angiography, 69 patients were divided into three groups, according to the anatomy of the vertebrobasilar system. In patients with the type I configuration, the vertebral artery on the affected side was dominant and had a sigmoidal course. The type II patients had the basilar artery curving mainly towards the affected side. The type III patients showed the basilar artery either running straight or curving toward the unaffected side. The relation of the anatomical configuration of these vessels with the perforating branches around the facial nerve exit zone was investigated. RESULTS: The posterior inferior cerebellar artery in type I patients (n=33) and the anterior inferior cerebellar artery in type II (n=5) and type III (n=31) patients were the most common offending arteries. More than half of the type I patients (n=20) showed no perforating branches around the facial nerve exit zone. However, the type II (n=3) and III patients (n=23) often showed one or more perforating branches around that region. CONCLUSIONS: The configuration of the vertebrobasilar system has a significant correlation with the presence of perforating branches near the site of microvascular decompression. These perforating vessels are often responsible for the difficulty encountered in mobilising the offending artery during the procedure.     

Relationship between the posterior cerebral artery and the cisternal segment of the oculomotor nerve.

The aim of this study was to evaluate the relationship between the cisternal segment of the oculomotor nerve and the posterior cerebral artery and its branches. The oculomotor nerve and the posterior cerebral artery of 15 cadaver brains (30 hemispheres) were examined using a surgical microscope. The dorsal portion of the cisternal segment of the oculomotor nerve had a close relationship with the P(1) and P(2) segments of the posterior cerebral artery in 100% of cases, the thalamoperforating arteries in 97%, the collicular arteries in 97%, the short circumferential arteries in 33% and the posterior medial choroidal arteries in 20%. The proximal portion of the nerve had a close relationship with the P(1) segment of the posterior cerebral artery, the thalamoperforating arteries, the collicular arteries and the short circumferential arteries, whereas the distal portion had a close relationship with the P(2) segment of the posterior cerebral artery and the posterior medial choroidal arteries. The oculomotor nerve was perforated by various arteries in different portions. These arteries were the thalamoperforating arteries in 10% of the hemispheres, the collicular arteries in 16% and the short circumferential arteries in 11%. It can be concluded that the dorsal portion of the cisternal segment of the oculomotor nerve has a close relationship with the branches arising from the P(1) and P(2) segments of the posterior cerebral artery. These arteries supply the cisternal segment of the oculomotor nerve.     

Perforating branches of the middle cerebral artery. Microanatomy and clinical significance of their intracerebral segments

Perforating branches of the middle cerebral arteries (MCA) were examined on the forebrain hemispheres of fourteen human brains. It was noticed that their intracerebral segments arose from the MCA main trunk, and its terminal and collateral (cortical) branches. They terminated in certain parts of the basal ganglia and internal capsule. The course, direction, shape, diameters and branches of these segments were examined in detail. Classification of all the vessels was made according to caliber. It was concluded that the size of lacunar infarcts depends on the caliber and ramification zone extent of the occluded perforating vessels. Diameters of the intracerebral segments of vessels ranged from 80 to 840 microns, of their terminal branches from 80 to 780 microns, and of the collateral branches from 50 to 400 microns. The average size of the ramification zone was: 41.6 X 15.5 mm for the entire perforating artery; 37.9 X 15.5 mm for the intracerebral segment; 23 X 13 mm for the terminal branches; 8.9 X 5.5 mm for larger collateral branches; and 2.6 X 1.4 mm for the smallest branches.     

Anatomy of the cerebellar arteries

Origin, course and distribution of the cerebellar arteries and of their branches are described. Anatomical drawings of the territory of these arteries are presented. They are based on a neuropathological study of 64 cases of cerebellar infarctions, the detailed study of which is reported elsewhere. The superior cerebellar artery (SCA) supplies a small brain stem territory, located on the dorsal tegmentum and the tectum of the upper part of the pons. The superior part of the cerebellum supplied by this artery includes the following lobules: lobulus anterior, lobulus simplex, lobulus semilunaris superior, and, in the vermis, lobulus centralis, culmen and clivus. The dentate nucleus belongs to this territory. The anterior inferior cerebellar artery (AICA) irrigates a ponto-cerebellar territory. It usually supplies the lateral territory of the lower part of the pons, the middle cerebellar peduncle, the flocculus and the neighbouring lobules of cerebellum. When the posterior inferior cerebellar artery (PICA) is hypoplastic, AICA takes over the territory usually supplied by the lateral branch of the PICA. The PICA always gives rami to the group of arteries supplying the dorsal medullary territory, but rarely participates to the supply of the lateral medullary territory. It supplies the lobulus semilunaris inferior, the lobulus gracilis, the lobulus biventer, the tonsilla cerebelli, and, in the vermis, the clivus, the tuber, the pyramis, the uvula and the nodulus. PICA never supplies the dentate nucleus. The flocculo-nodular lobe is usually supplied by 2 arteries: the flocculus is supplied by the AICA and the nodulus is supplied by the PICA.     

Anastomoses among the thalamoperforating branches of the posterior cerebral artery

Thirty-three injected human brains were examined, and anastomotic vessels were found in 26 (79%) of them. Anastomoses varied in number from one to six. The mean diameter was 148 microns, and the mean length was 3.3 mm. Anastomoses were observed among the following: the branches of the single thalamoperforating vessel of the posterior cerebral artery (PCA), the individual thalamoperforating arteries of the same PCA, the thalamoperforating vessels and branches of the basilar and superior cerebellar arteries on the same side, the peduncular branches of the PCA and ipsilateral branches of the basilar and superior cerebellar arteries, and the thalamoperforating arteries on one side and various contralateral vessels. Anastomoses could be important components of collateral circulation in occlusive cerebrovascular diseases.     

Infarction in the territory of the medial branch of the posterior inferior cerebellar artery.

We report 10 cases of cerebellar infarction in the territory of the medial branch of the posterior inferior cerebellar artery (mPICA). Axial sections on MRI through the middle of the medulla and the cerebellum showed the infarction as a triangular area with a dorsal base and a ventral apex directed towards the fourth ventricle. The infarct also involved the lateral and dorsal medulla when the mPICA supplied all or part of these regions. Three clinical patterns were observed: 1) pseudolabyrinthine signs with or without dysmetria and ataxia when the medulla was spared; marked axial lateropulsion was present in most cases; 2) complete or incomplete Wallenberg's syndrome, when the medulla was involved; 3) silent infarction. These syndromes are precisely those previously attributed to PICA occlusion without distinction of the branch involved. No alteration of consciousness was recorded and spontaneous recovery was the rule. Cerebellar infarction in the distribution of the mPICA can be regarded as a benign condition with a good prognosis.