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 lower basilar artery

Abstract

This study was designed to study the microvascular anatomy of the basilar artery between the superior cerebellar artery and the vertebrobasilar junction (i.e. the lower basilar artery). Twenty unfixed brains were injected with silicone rubber solution and studied with a Zeiss OPMI microscope. The length of this segment of the basilar artery was 28.1 + 1.35 mm and its course was straight in 9 (45%) brains, curved in 7 (35%) and tortuous in 4 (20%). The total number of perforators found in 20 brains was 340 with an average of 17 per brain. Of these, 118 (34.7%) were median and 222 ( 65.2%) were lateral. Median branches had a mean length of 5.8 + 1.25 mm, whereas left and right lateral branches had a mean length of 16 + 1.25 mm and 16 + 1.58 mm respectively.     

Microsurgical anatomy of the lower basilar artery.

This study was designed to study the microvascular anatomy of the basilar artery between the superior cerebellar artery and the vertebrobasilar junction (i.e. the lower basilar artery). Twenty unfixed brains were injected with silicone rubber solution and studied with a Zeiss OPMI microscope. The length of this segment of the basilar artery was 28.1 + 1.35 mm and its course was straight in 9 (45%) brains, curved in 7 (35%) and tortuous in 4 (20%). The total number of perforators found in 20 brains was 340 with an average of 17 per brain. Of these, 118 (34.7%) were median and 222 (65.2%) were lateral. Median branches had a mean length of 5.8 + 1.25 mm, whereas left and right lateral branches had a mean length of 16 + 1.25 mm and 16 + 1.58 mm respectively.     

Rotational vertebral artery syndrome due to compression of nondominant vertebral artery terminating in posterior inferior cerebellar artery

Rotational vertebral artery syndrome (RVAS) is characterized by recurrent attacks of paroxysmal vertigo, nystagmus, and ataxia induced by head rotation. We report on a patient who developed atypical RVAS due to compression of the vertebral artery (VA) terminating in the posterior inferior cerebellar artery (PICA). A 59-year-old man suffered from vertigo and nystagmus induced by leftward head rotation and oculography showed right beating horizontal-torsional and downbeat nystagmus. Cerebral angiography showed hypoplastic right VA terminating in PICA without connection to the basilar artery. The basilar artery received its flow from the left VA only and branched out both anterior inferior cerebellar arteries. Cerebral angiography revealed a complete occlusion of the right distal VA at the level of the C1–2 junction when the head was rotated to a leftward position. In contrast, the blood flow through the left vertebral and basilar arteries remained intact while turning the head to either side. The hemodynamic compromise observed in our patient with RVAS indicates that isolated vertigo and nystagmus may occur due to transient ischemia of the inferior cerebellum or lateral medulla.     

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.     

Anomalous Origin of the Middle Meningeal Artery from the Basilar Artery: A Case Report

Anomalous courses, anastomoses, and origins of the middle meningeal artery have often been described in the literature; however origin from the basilar artery or its branches is exceedingly rare with only five previous reports. We describe a middle meningeal artery originating from a large lateral pontine branch of the basilar artery. The lateral pontine branch also supplied most of the cerebellar hemispheric territory normally vascularized by both the anterior inferior cerebellar artery and posterior inferior cerebellar artery. We discuss the anatomy and possible embryological development of middle meningeal origin from the basilar artery.     

Imaging of the intracranial vertebrobasilar system using color-coded ultrasound.

BACKGROUND: Anatomic variety and difficult accessibility of the vertebrobasilar arteries pose considerable problems to conventional ultrasound. We evaluated the diagnostic potential of transcranial color-coded sonography in the distal part of this system. METHODS: We insonated the intracranial section of the vertebrobasilar arteries through the foramen magnum window in 24 healthy individuals using a Doppler color flow imaging system in connection with a 2.5-MHz sector transducer. Magnetic resonance images in special inclination planes were performed and compared with the color-coded duplex images in five cases. RESULTS: The B-mode image of the craniocervical junction and the intracranial parenchymal structures in addition to the color-coded blood flow allowed an unambiguous identification of the vertebrobasilar arteries (vertebral artery, 96%; basilar artery, 79%; and posterior inferior cerebellar artery, 50%). Blood flow velocities were measured considering the insonation angles: vertebral arteries, 50/24 cm/sec (30 degrees); basilar artery, 59/28 cm/sec (4 degrees); and posterior inferior cerebellar artery, 56/30 cm/sec (20 degrees) [peak systolic/end diastolic blood flow velocity (mean angle correction)]. CONCLUSIONS: Transcranial color-coded sonography enables accurate identification and differentiation of the intracranial vertebrobasilar arteries and improves accuracy of Doppler measurements. It may prove useful for evaluation of tortuosity and for hemodynamic studies in this vascular territory.     

Infarcts presenting with a combination of medial medullary and posterior inferior cerebellar artery syndromes

Cerebellar and medial medullary infarctions are well-known vertebrobasilar stroke syndromes. However, their development in a patient with distal vertebral artery occlusion has not been previously reported. A 49-year-old man with longstanding hypertension suddenly developed vertigo, right-sided Horner syndrome, and left-sided weakness. An MRI of the brain showed acute infarcts in the right inferior cerebellum (posterior inferior cerebellar artery territory) and the right upper medial medulla (direct penetrating branches of vertebral artery). Magnetic resonance angiogram showed occlusion of the distal vertebral artery on the right side. Atherothrombotic occlusion of the distal vertebral artery may cause this unusual combination of vertebrobasilar stroke.     

Rotational vertebral artery syndrome

Whether the rotational vertebral artery syndrome (RVAS), consisting of attacks of vertigo, nystagmus and tinnitus elicited by head-rotation induced compression of the dominant vertebral artery (VA), reflects ischemic dysfunction of uni- or bilateral peripheral or central vestibular structures, is still debated. We report on a patient with bilateral high-grade carotid stenoses, in whom rightward headrotation led to RVAS symptoms including a prominent nystagmus. Three-dimensional kinematic analysis of the nystagmus pattern, recorded with search coils, revealed major downbeat nystagmus with minor horizontal and torsional components. Magnetic resonance angiography demonstrated a hypoplastic right VA terminating in the posterior inferior cerebellar artery, a dominant left VA, and a hypoplastic P1-segment of the left posterior cerebral artery (PCA) that was supplied by the left posterior communicating artery (PCoA). The right PCA and both anterior inferior cerebellar arteries were supplied by the basilar artery. The right PCoA originated from the right internal carotid artery. Color duplex sonography showed severe reduction of diastolic blood flow velocities in the left VA during RVAS attacks. The nystagmus pattern can be best explained by vectorial addition of 3D sensitivity vectors of stimulated right and left anterior and horizontal semicircular canals with slightly stronger stimulation on the left side. We hypothesize that in RVAS, compression of dominant VA leads to acute vertebrobasilar insufficiency with bilateral, but asymmetric ischemia of the superior labyrinth. With regard to RVAS etiology, our case illustrates a type of pure vascular RVAS. Severity of attacks markedly decreased after successful bilateral carotid endarterectomy.     

Bilateral sudden deafness as a prodrome of anterior inferior cerebellar artery infarction

BACKGROUND: Acute ischemic stroke in the distribution of the anterior inferior cerebellar artery is known to be associated with hearing loss, facial weakness, ataxia, nystagmus, and hypalgesia. There have been few reports on bilateral deafness and vertebrobasilar occlusive disease. Furthermore, previous reports have not emphasized the inner ear as a localization of bilateral deafness. OBJECTIVE: To describe the presentation of acute ischemic stroke in the distribution of the anterior inferior cerebellar artery as sudden bilateral hearing loss with minimal associated signs. DESIGN AND SETTING: Case report and tertiary care hospital. PATIENT: A 66-year-old man with diabetes mellitus developed sudden bilateral deafness, unilateral tinnitus, and vertigo 7 days before the onset of dysarthria, facial weakness, and ataxia. T2-weighted magnetic resonance imaging scans showed hyperintensities in the right lateral pons and right middle cerebral peduncle and a possible abnormality of the left middle cerebellar peduncle. A magnetic resonance angiogram showed moderately severe stenosis of the distal vertebral artery and middle third of the basilar artery. The patient's right limb coordination and gait improved steadily over several weeks, but there was no improvement in hearing in his right ear. CONCLUSIONS: The relatively isolated onset of deafness as well as the severity and persistence of the hearing loss led us to conclude that the hearing loss in this case was likely due to prominent hypoperfusion of the internal auditory artery, with labyrinthine infarction as the earliest event. Vertebrobasilar occlusive disease should be considered in the differential diagnosis of sudden bilateral deafness.     

A case of ischemic disturbance of inner ear

We reported a 51-year-old male with ischemic disturbance of right inner ear resembling Meniere's disease. The patient had a sudden-onset episode of vertigo, right severe hearing disturbance, nausea, vomiting and gait disturbance. Two days after, he had hypersomnia, vertical gaze palsy, double vision, left Horner's sign, and sensory disturbance of pain and temperature of right half body involving face. Brain MRI disclosed high intensity area in T2-weighted image and proton density in bilateral paramedian thalamo-mesencephalic region and right cerebellum (area of the anterior inferior cerebellar artery). Cerebral angiography showed 90% or more stenosis of the right vertebral artery, 50% stenosis of the left vertebral artery before the posterior inferior cerebellar artery (PICA), and 60% stenosis of distal portion of the basilar artery. Furthermore, stem portion of the posterior cerebral artery, and the right anterior cerebellar artery and the left vertebral artery after the PICA were absent or occluded. Right deafness was evaluated to be Jerger type II, namely disturbance of inner ear. Caloric tests showed no response, and right auditory brainstem response showed no waves. Main cause of this vertigo and right deafness was considered to be disturbance of inner ear due to ischemia of right labyrinthine artery, though this patient was not a typical case of the anterior cerebellar artery syndrome. Ischemic disturbances of inner ear have been reported only in patients with the anterior cerebellar artery syndrome, therefore this patient who had only acute ischemic disturbance of inner ear and did not have disturbance of caudo-lateral portion of the pons was considered to be very rare.     

后循环动脉瘤显微外科手术治疗

目的 探讨后循环动脉瘤手术适应证和治疗效果.方法 纳入42例共44个后循环动脉瘤,包括基底动脉动脉瘤26例(27个)、椎动脉动脉瘤16例(17个).其中15例分别行颈外动脉-大脑后动脉P2段(4例)、颈内动脉-大脑后动脉P2段(2例)、颌内动脉-大脑后动脉P2段(2例)、椎动脉颅内外段(2例)、枕动脉.小脑后下小动脉(5例)搭桥联合动脉瘤孤立术;余27例行单纯动脉瘤夹闭术.结果 经随访共37例(基底动脉顶端动脉瘤14例、基底动脉主干动脉瘤3例、椎动脉动脉瘤9例、小脑后下动脉动脉瘤5例、大脑后动脉P1～P2段交界处动脉瘤4例、小脑上动脉动脉瘤l例和小脑前下动脉动脉瘤1例)患者恢复正常生活活动能力,无一例发生手术相关性神经功能障碍,恢复良好率达88.09%.其余5例患者,1例(基底动脉顶端动脉瘤)术后出现严重神经功能缺损症状与体征,生活不能自理;2例(1例基底动脉顶端动脉瘤、1例基底动脉主干动脉瘤)因术后发生脑干缺血,围手术期死亡;2例(椎动脉动脉瘤)复发患者经再次治疗康复.结论 对于不宜直接行手术夹闭的后循环动脉瘤,为了避免因夹闭动脉瘤和延长临时阻断载瘤动脉时间而发生术后脑缺血事件.可选择颅内外血管搭桥联合动脉瘤孤立术,以避免动脉瘤夹闭术带来的危险.     

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.     

The posterior inferior cerebellar artery arising from the internal carotid artery directly: a variant of the persistent primitive hypoglossal artery]

We reported a rare case of the posterior inferior cerebellar artery arising from the internal carotid artery directly. A 33-year-old male was admitted to our hospital with the complaint of throbbing type headache. CT showed no abnormal findings. A saccular aneurysm at the bifurcation of the left middle cerebral artery was revealed by MR angiography and the left internal carotid angiography. The right internal carotid angiography demonstrated an anomalous branch originating at the level of the C1/2 in the cervical portion of the internal carotid artery. This branch terminated as the posterior inferior cerebellar artery without an interposed segment of the vertebro-basilar artery. The ipsilateral vertebral artery was aplasia. T2-weighted MR image showed a flow-void penetrating the right hypoglossal canal. This vessel was confirmed an artery passing through the hypoglossal canal with the source images of the three-dimensional time-of-flight MR angiography. We diagnosed it as a kind of variant of the persistent primitive hypoglossal artery. The persistent primitive hypoglossal artery is composed of the proximal segment derived from the primitive hypoglossal artery, and the distal segment consisting of portions of the lateral anastomotic channels (primitive lateral basillo-vertebral anastomosis) which give rise to the posterior inferior cerebellar artery. We speculated that this variant resulted from the persistence of the proximal segment, which communicated with the stem of the posterior inferior cerebellar artery via the distal segment, and next, the disconnection of the posterior inferior cerebellar artery origin with the vertebral artery due to the aplasia of right vertebral artery and the involution of the distal segment connected to the basilar artery.     

小脑后下动脉解剖变异致双侧小脑梗死2例报道并文献复习

目的 探讨小脑后下动脉(posterior inferior cerebellar artery, PICA)解剖变异致双侧小脑梗死的临床特征及发病机制。方法 对2例经颅脑MRI确诊的双侧小脑梗死患者采用CT血管造影(CTA)、磁共振血管成像(MRA)或数字减影血管造影(DSA)显示其头颈部血管,从而了解后循环血管的形态特征并复习相关文献。结果 病例1经DSA证实左侧椎动脉较细,远端管腔闭塞,通过右椎动脉代偿供血原左侧PICA供血区但欠充分,双侧PICA共同起源于右侧椎动脉。病例2经CTA证实右侧椎动脉较左侧明显细且远端显示欠清,MRA示双侧PICA共同起源于左侧椎动脉。结论 2例双侧小脑梗死患者均存在一侧椎动脉优势供血,且双侧PICA共同起源于该侧椎动脉。在该解剖变异基础上一侧椎动脉发生病变时可出现双侧小脑梗死。因此,在临床中出现双侧小脑梗死时临床医师不能忽略这一解剖变异基础。     

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]     

Obliteration of bilateral dissecting aneurysms of the vertebral arteries following repeated subarachnoid hemorrhage: A case report

Abstract

A 51-year-old man presented with loss of consciousness when he underwent urological examination at another hospital. CT scans showed subarachnoid hemorrhage, and cerebral angiography showed bilateral dissecting aneurysms of the vertebral arteries. Following ventricular drainage, the lesion was managed conservatively with blood pressure control but again ruptured on day 8. Cerebral angiography revealed narrowing of both the dissecting aneurysms. On day 11, the right vertebral artery had been spontaneously obliterated and the right dissecting aneurysm was filled in a retrograde fashion via the left vertebral artery. Proximal occlusion of the right vertebral artery was performed to prevent recanalization. Two months later, cerebral angiography revealed that both vertebral arteries were obliterated and the basilar artery and right posterior inferior cerebellar artery were filled via the right posterior communicating artery. The present case demonstrated that the hemodynamic status of bilateral dissecting aneurysms of the vertebral artery changed variably indicating the necessity of careful angiographic observation.     

A case of brain stem infarction with bilateral hearing impairment and tinnitus at the onset

We reported a 49-year-old male with brain stem infarction who had bilateral hearing impairment and tinnitus at the onset and subsequently developed various neurological symptoms, including bilateral lateral inferior pontine syndrome, one and a half syndrome and upward gaze palsy. Although CT scan failed to reveal any abnormalities initially, MRI revealed symmetrical foci bilaterally from the lateral inferior pons to the middle cerebellar peduncle, as well as in the paramedian portion of the mid-pons. Cerebral angiography: The left vertebral artery (VA) occluded at the 4th segment. The right VA showed severe stenosis at the 4th segment. The basilar artery (BA) was found to be occluded in the lower 1/3 below the clivus. Furthermore, CAG demonstrated upper portion of the BA, bilateral superior cerebellar artery and posterior cerebral artery via the posterior communicating artery, but the bilateral anterior inferior cerebellar arteries (AICAs) were absent or occluded. Neuroradiological findings suggested ischemia in the bilateral AICA and the middle portion of the BA. Bilateral hearing impairment rarely accompanies cerebrovascular disorders. This case of bilateral hearing impairment, tinnitus at the onset, followed by bilateral lateral inferior pontine syndrome was considered to be an extremely rare pathological condition.     

Bilateral deafness as a prodromal symptom of basilar artery occlusion.

Bilateral deafness is a rare but possible symptom for ischemia of the vertebrobasilar system, primarily derived from occlusion of anterior inferior cerebellar arteries or their branches. Patients 1 and 2 developed sudden bilateral deafness, soon followed by coma. The proximal segment of the basilar artery was occluded due to atherothrombosis in Patient 1 and arterial dissection in Patient 2. Thrombolytic therapy failed to recanalize the basilar arterial flow. Both patients died of extensive infarction in the vertebrobasilar arterial territory. Sudden bilateral deafness can be a warning sign of imminent brainstem ischemia by occlusion of the basilar artery regardless of age. Prompt and intensive management for stroke is needed for patients with sudden bilateral deafness.     

Combination of infarctions in the posterior inferior cerebellar artery and anterior spinal artery territories

After an episode of vasodilator-induced systemic hypotension, a 75-year-old man developed ocular lateropulsion to the right, left-side-dominant quadriparesis, loss of superficial sensation below C4 dermatome level, and anuresis. Magnetic resonance imaging (MRI) showed infarcts in the right cerebellar hemisphere (posterior inferior cerebellar artery territory) and the upper cervical cord (anterior spinal artery territory); the combination of posterior inferior cerebellar artery (PICA) and anterior spinal artery (ASA) infarcts has not been reported previously. Angiography revealed severe stenosis in the bilateral vertebral arteries. Hemodynamic hypoperfusion of the stenotic vertebral arteries may cause this unusual combination.