Microsurgical anatomy of the superficial veins of the cerebrum

Microneurosurgical management of aneurysms at the A2 segment of anterior cerebral artery (proximal pericallosal artery) and its frontobasal branches

BACKGROUND

Aneurysms originating from the A2 segment of ACA and its frontobasal branches are rare, forming less than 1% of all IAs. There are only few reports on management of A2As. In this article, we review the practical anatomy, preoperative planning, and avoidance of complications in the microsurgical dissection and clipping of A2As.

METHODS

This review, and the whole series on IAs, is mainly based on the personal microneurosurgical experience of the senior author (JH) in two Finnish centers (Helsinki and Kuopio), which serve, without patient selection, the catchment area in Southern and Eastern Finland.

RESULTS

These two centers have treated more than 10000 patients with IAs since 1951. In the Kuopio Cerebral Aneurysm Database of 3005 patients and 4253 IAs, there were 35 patients carrying 35 A2As, forming 1% of all patients with IAs, 0.8% of all IAs, and 3% of all ACA aneurysms. Twenty-one (60%) patients presented with ruptured A2As with ICH in 11 (52%) and IVH in 7 (33%). Nineteen patients (54%) had multiple aneurysms.

CONCLUSIONS

A2As are often small, even when ruptured, with relatively wide base, and they are frequently associated with ICHs of IVHs. Our data suggest that A2As rupture at smaller size than IAs in general. The challenge is to select appropriate approach, locate the aneurysm deep inside the interhemispheric fissure, and to clip the neck adequately without obstructing branching arteries at the base. Unruptured A2As also need microneurosurgical clipping even when they are small.

Dural Entrance of the Bridging Vein into the Transverse Sinus Provides a Reliable Measure for Preoperative Planning: An Anatomic Comparison between Cadavers and Neuroimages

Objective:

Understanding the anatomy of the transverse sinus and its associated bridging veins (BVs) is essential to approaching the posterior and middle incisural space. The venous phase of neuroimages has received increasing attention in preoperative planning. The aims of this study are to identify anatomic features of the dural entrance of the BVs into the transverse sinus on the cadaver and to correlate such features with those of digital subtraction angiography (DSA), computed tomographic venography (CTV), and magnetic resonance venography (MRV).

Methods:

A total of 30 adult cadavers and 76 patients were examined through anatomic dissection and DSA, CTV, and MRV, respectively. The number, diameter, and location of the BVs entering the sinus were measured, and comparisons were made between the cadavers and neuroimages.

Results:

We found that the way BVs entered the transverse sinus varied but was identifiable in DSA, CTV, and MRV images. Compared with the cadavers, DSA, CTV, and MRV revealed less than 50% of the BV entering the sinus because the smaller BVs were not seen on the neuroimages. However, the distribution pattern of the dural entrance of the BVs into the transverse sinus was relatively consistent between cadavers and neuroimages.

Conclusion:

Unique anatomic features of the dural entrance of a BV into the transverse sinus in the cadaver correspond to those evident in neuroimages; thus, identification of the dural entrance of the BVs with neuroimaging modalities provides a reliable measure for preoperative planning.

Medial Sphenoid Ridge Meningiomas: Classification, Microsurgical Anatomy, Operative Nuances, and Long-Term Surgical Outcome in 35 Consecutive Patients

Objective:

On the basis of contemporary multiplanar imaging, microsurgical observations, and long-term follow-up in 60 consecutive patients with sphenoid ridge meningiomas, we propose a modification to Cushing's classification of these tumors. This article will concentrate on patients from this series with global medial sphenoid ridge tumors.

Methods:

Data were collected prospectively for 35 patients with global meningiomas arising from the medial portion of the sphenoid ridge that were surgically treated between 1982 and 2002.

Results:

All patients were followed for the entire length of this study (mean, 12.8 yr). The tumor size ranged from 2 to 8 cm (mean, 4.5 cm). Of the 24 patients with purely intradural tumors, four (17%) had Simpson Grade I and 19 had Simpson Grade II resections; 23 (96%) had gross total resections. Of the 11 patients with tumors extending extradurally (i.e., cavernous sinus), one (9%) patient had a Simpson Grade II resection, whereas nine (82%) had Simpson Grade III resections, with the latter being all visible tumor removed except that in the cavernous sinus. One (9%) of these 11 patients had a gross total resection, and 9 (82%) had radical resections, with the latter defined as total removal of all intradural tumor. The overall morbidity rate was 18%. There was no surgical mortality or symptomatic cerebral infarction.

Conclusion:

An accurate classification of global medial sphenoid meningiomas is mandatory to gain insight into their clinical behavior and for understanding the long-term efficacy and safety of available treatment options. Primary medial sphenoid ridge tumors consistently involve the unilateral arteries of the anterior cerebral circulation, and therefore, the resection of tumor from around these arteries is the most important operative nuance for their safe excision.

Microneurosurgical management of proximal anterior cerebral artery aneurysms

BACKGROUND

Aneurysms originating from the proximal segment of anterior cerebral artery (A1As) are rare, forming less than 1% of all IAs. There are only few reports on microneurosurgical management of A1As. In this article, the authors review the practical anatomy, preoperative planning, and avoidance of complications in the microsurgical dissection and clipping of A1As.

METHODS

This review, and the whole series on IAs, is mainly based on the personal microneurosurgical experience of the senior author (JH) in 2 Finnish centers (Helsinki and Kuopio), which serve without patient selection the catchment area in Southern and Eastern Finland.

RESULTS

These 2 centers have treated more than 10,000 patients with aneurysm since 1951. In the Kuopio Cerebral Aneurysm Database of 3005 patients with 4253 aneurysms, there were 23 patients carrying 23 A1As, forming 0.8% of all patients with aneurysm, 0.5% of all aneurysms, and 2% of all ACA aneurysms. Twelve (52%) patients presented with ruptured A1As with ICH in 3 (25%) and IVH in 2 (17%). Seventy percent of patients had at least 1 associated aneurysm.

CONCLUSIONS

Aneurysms arising from A1 are usually small, with a fragile wall. Our data suggest that A1As rupture at smaller size than IAs in general. Because of their small size and involvement of perforating arteries at their base, microneurosurgical clipping is the method of choice in treatment of ruptured A1As. Unruptured A1As also need microneurosurgical clipping even when they are small.

Venous Anatomy of the Sphenoparietal Sinus: Evaluation by MR Imaging

SUMMARY

The termination of the superficial middle cerebral vein (SMCV) has been described as entering or being partially equivalent to the venous sinus coursing under the lesser sphenoid wing, which has classically been called the sphenoparietal sinus. However, the recent literature reports that the SMCV is not connected to the sphenoparietal sinus. In this study, the venous anatomy was evaluated to clarify the anatomy of the sphenoparietal sinus and the termination of the SMCV. Magnetic resonance imaging (MRI) was performed on 1.5-T superconductive units using a three-dimensional fast spoiled gradientrecalled acquisition in the steady state (3-D fast SPGR) sequence with fat suppression in a total of 48 sides of 24 patients. Coronal source images and reconstructed axial images were displayed on the Advantage Window Console, and connections to the cavernous sinus were then evaluated for the venous sinus coursing under the lesser sphenoid wing (hereafter called the sinus of the lesser sphenoid wing), the middle meningeal vein, and the SMCV. The following findings were observed bilaterally in all patients. The sinus of the lesser sphenoid wing was connected medially with the cavernous sinus and laterally with the anterior branch of the middle meningeal vein near the pterion. The anterior branch of the middle meningeal vein entered the bony canal laterally above the junction with the sinus of the lesser sphenoid wing and coursed along the inner table of the skull or emerged into the diploic vein, indicating its parietal portion. Although the termination of the SMCV had several patterns, the SMCV was not connected with the sinus of the lesser sphenoid wing in any of the patients. The sphenoparietal sinus is considered to consist of the sinus of the lesser sphenoid wing and the parietal portion of the anterior branch of the middle meningeal vein; these were identified as venous structures distinct to the SMCV.

Dural arteriovenous fistula of the sphenobasilar sinus with concomitant meningioma: case report and review of the literature

Dural arteriovenous fistula of the sphenobasilar sinus is a true but rare lesion that connects the meningeal arteries from both the external and internal carotid arteries to the superficial middle cerebral vein (SMCV) and dural sinus. It must be distinguished from other dural arteriovenous fistulas (DAVFs) of the middle cranial fossa, such as cavernous DAVFs and sphenoparietal sinus DAVF, because of differences in the treatment and outcome between these DAVFs. Two patients with sphenobasilar sinus DAVFs reported in the literature have been identified, but they did not simultaneously harbor intracranial meningiomas. To the best of the authors' knowledge, the patient described here is the first case that concomitantly harbors a sphenobasilar sinus DAVF and intracranial meningioma. A 42-year-old man presented with acute subarachnoid hemorrhage. Angiography demonstrated a DAVF of the sphenobasilar sinus with a giant venous aneurysm of the SMCV. After transarterial embolization, the fistula was successfully obliterated and the giant venous aneurysm was resected microsurgically. A fortuitous small meningioma at the anterior clinoid was found and removed during the operation. The patient recovered excellently and resumed his normal activities. The relevant literature is reviewed and discussed.

Imaging of cerebral venous thrombosis: current techniques, spectrum of findings, and diagnostic pitfalls

Cerebral venous thrombosis is a relatively uncommon but serious neurologic disorder that is potentially reversible with prompt diagnosis and appropriate medical care. Because the possible causal factors and clinical manifestations of this disorder are many and varied, imaging plays a primary role in the diagnosis. Magnetic resonance (MR) imaging, un-enhanced computed tomography (CT), unenhanced time-of-flight MR venography, and contrast material-enhanced MR venography and CT venography are particularly useful techniques for detecting cerebral venous and brain parenchymal changes that may be related to thrombosis. To achieve an accurate diagnosis, it is important to have a detailed knowledge of the normal venous anatomy and variants, the spectrum of findings (venous sinus thrombi and recanalization, parenchymal diffusion or perfusion changes or hemorrhage), other potentially relevant conditions (deep venous occlusion, isolated cortical venous thrombosis, idiopathic intracranial hypertension), and potential pitfalls in image interpretation.

The dural entrance of cerebral bridging veins into the superior sagittal sinus: an anatomical comparison between cadavers and digital subtraction angiography

INTRODUCTION

Intracranial venous structures have received increasing attention due to improved neuroimaging techniques and increased awareness of cerebral venous disease. To date, few studies have attempted to investigate the dural entrance of the cerebral bridging vein (BV). The aim of this study was to use the superior sagittal sinus (SSS) as an example to identify anatomical features of the dural entrance of the BVs into the SSS in both human cadavers and digital subtraction angiography (DSA) images.

METHODS

A total of 30 adult and 7 fetal human cadavers and 36 patients were examined with anatomical dissections, vascular casting and DSA. The number, diameter and angle of the BVs entering the SSS were measured and compared between the cadavers and DSA images.

RESULTS

The results demonstrated that (1) the way a BV entered the SSS varied in three dimensions, and thus the BV dural entrance was difficult to precisely localize by DSA, (2) the distribution pattern of the dural entrance of the BVs into the SSS was relatively constant and a nontributary segment of the SSS was centered at the coronal suture and was identifiable by DSA, and (3) nearly all the BVs (97%, 561/581) entered the SSS at an angle opposite to the direction of blood flow.

CONCLUSION

Unique anatomical features of the dural entrance of a BV into the SSS should be considered in neuroimaging interpretation of the sinus and its associated veins.

Biomechanical properties of the superior sagittal sinus-bridging vein complex

Finite element models (FEM) of the head are frequently used to simulate traumatic brain injury, leading to a better understanding of brain injury tolerance. The strength of a FEM of the head is dependent on the use of correct material characteristics, experimentally derived for each intracranial tissue, including parasagittal bridging veins (BV). These veins are prone to rupture in their subdural portion upon head impact, giving rise to an acute subdural hematoma (ASDH). The junction of these veins to the superior sagittal sinus (SSS) has been described as an area with distinct vein wall architecture. To understand the biomechanical characteristics of acute subdural hematoma, we studied the SSS-BV complex by loading it to failure in a tensile test. 37 BVs from 9 fresh cadavers were dissected, leaving small strips of SSS attached to the veins. The units were clamped on the SSS and the cortical end of the BV. Strain rates ranged from 0.1-3.8 s(-1). From force-time and strain-time histories, we calculated ultimate strain (epsilon(U)), ultimate stress (sigma(U)), yield strain (epsilon(Y)), yield stress(sigma(Y)) and Young's modulus (E). A mixed-model multivariate analysis of variance (MANOVA) was used to study correlations and strain rate sensitivity of these parameters. We found no strain rate sensitivity. The biomechanical response of the SSS-BV unit in this study was found to be stiffer than reported biomechanical behavior of bridging veins. We conclude that the SSS-BV junction plays an important role in bridging vein rupture, and warrants further investigation to provide FEM with correct material properties for bridging veins.

Mechanics of acute subdural hematomas resulting from bridging vein rupture

Object

Based on data from primate experiments it is known that rotational acceleration in the sagittal plane and in a forward direction is most likely to produce acute subdural hematomas due to bridging vein rupture. For protection against these lesions, knowledge of rotational acceleration tolerance levels in humans is required. In the present study the authors analyze human tolerance levels for bridging vein rupture by performing head impact tests in cadavers.

Methods

Ten unembalmed cadavers were subjected to 18 occipital impacts producing head rotation in the sagittal plane with varying rotational acceleration magnitudes and pulse durations. Rotational acceleration was calculated from the linear acceleration histories recorded by three uniaxial accelerometers mounted on the side of the head. Bridging vein ruptures were detected by injecting contrast dye into the superior sagittal sinus under fluoroscopy and by autopsy procedures. Bridging vein ruptures were produced in six head impact tests: one test with a pulse duration of 5.2 msec and a peak rotational acceleration of 13,411 rad/second2; three tests with a pulse duration between 7 and 8 msec and a peak rotational acceleration of 12,558, 10,607, and 8567 rad/second2; and two tests with a pulse duration longer than 10 msec and a peak rotational acceleration as low as 5267 rad/second2.

Conclusions

This is the only cadaveric study of bridging vein rupture focused on short pulse durations, which are usually associated with falls. The data suggest a tolerance level of approximately 10,000 rad/second2 for pulse durations shorter than 10 msec, which seems to decrease for longer pulse durations.

Evaluation of drainage patterns of the major anastomotic veins on the lateral surface of the cerebrum using three-dimensional contrast-enhanced MP-RAGE sequence

BACKGROUND AND PURPOSE

Three-dimensional (3D) contrast-enhanced magnetization-prepared rapid gradient-echo (MP-RAGE) sequence has been reported useful for evaluation of the intracranial venous structures. The purpose of this study is to assess the patterns of the major anastomotic veins on the lateral surface of the cerebrum using MP-RAGE sequence.

METHODS

MP-RAGE images in consecutive 100 patients (200 sides) were reviewed by two neuroradiologists in consensus to evaluate drainage patterns of the superficial middle cerebral vein (SMCV), the vein of Labbe, and the Trolard vein.

RESULTS

MP-RAGE images clearly depicted the major anastomotic veins and their draining vessel. The dominant vein was the Trolard vein in 12%, the vein of Labbe in 36%, SMCV in 38%, and all three veins in 14%. The vein of Labbe was entered the transverse sinus in 80% and superior petrosal sinus in 4%. Undeveloped type of the vein of Labbe was seen in 16%. The SMCVs were entered the sphenoparietal sinus in 57%, the cavernous sinus in 19%, and the emissary vein in 5%. Basal type of the SMCVs was seen in 3% and undeveloped type in 16%. It was difficult to differentiate the Trolard vein from other cortical veins, if it was not dominant. In the most cases with the dominant Trolard vein, it located at the level of the post central vein.

CONCLUSION

With MP-RAGE sequence, it is easy to identify the variation of the major anastomotic veins. Such information may be helpful to reduce the risk of damage on these important veins at surgery.

Concussion in Professional Football: Brain Responses by Finite Element Analysis: Part 9

OBJECTIVE

Brain responses from concussive impacts in National Football League football games were simulated by finite element analysis using a detailed anatomic model of the brain and head accelerations from laboratory reconstructions of game impacts. This study compares brain responses with physician determined signs and symptoms of concussion to investigate tissue-level injury mechanisms.

METHODS

The Wayne State University Head Injury Model (Version 2001) was used because it has fine anatomic detail of the cranium and brain with more than 300,000 elements. It has 15 different material properties for brain and surrounding tissues. The model includes viscoelastic gray and white brain matter, membranes, ventricles, cranium and facial bones, soft tissues, and slip interface conditions between the brain and dura. The cranium of the finite element model was loaded by translational and rotational accelerations measured in Hybrid III dummies from 28 laboratory reconstructions of NFL impacts involving 22 concussions. Brain responses were determined using a nonlinear, finite element code to simulate the large deformation response of white and gray matter. Strain responses occurring early (during impact) and mid-late (after impact) were compared with the signs and symptoms of concussion.

RESULTS

Strain concentration "hot spots" migrate through the brain with time. In 9 of 22 concussions, the early strain "hot spots" occur in the temporal lobe adjacent to the impact and migrate to the far temporal lobe after head acceleration. In all cases, the largest strains occur later in the fornix, midbrain, and corpus callosum. They significantly correlated with removal from play, cognitive and memory problems, and loss of consciousness. Dizziness correlated with early strain in the orbital-frontal cortex and temporal lobe. The strain migration helps explain coup-contrecoup injuries.

CONCLUSION

Finite element modeling showed the largest brain deformations occurred after the primary head acceleration. Midbrain strain correlated with memory and cognitive problems and removal from play after concussion. Concussion injuries happen during the rapid displacement and rotation of the cranium, after peak head acceleration and momentum transfer in helmet impacts.

[Epidural hematoma at the vertex: case report]

We report the unusual case of a 37 years old man with an epidural traumatic hematoma at the vertex with intracranial hypertension symptoms. The diagnostic was achieved with coronal cranial tomographic scans and a craniotomy was performed for hematoma removal.

Three-dimensional Computed Tomography Angiography of the Galenic System for the Occipital Transtentorial Approach

The venous variations of the galenic system were evaluated using three-dimensional computed tomography angiography (3D-CTA) to assess the influence on the occipital transtentorial approach in 150 patients who underwent 3D-CTA as a routine screening examination for cerebrovascular diseases. The variations of the vein of Galen with its tributaries, the tentorial sinus, and the veins around the tentorium were evaluated in multiple intensity projections and stereoscopic images. The angle between the vein of Galen and the straight sinus was 67.1 +/- 31.9 degrees (mean +/- SD). Observation of the pineal body from the direction of the approach tended to extend to the quadrigeminal bodies in acute angle cases, and to the third ventricle in obtuse angle cases. Bilateral internal cerebral veins (ICVs) joined in the anterior portion were associated with a long vein of Galen, or in the posterior portion with a short vein of Galen. The distance between the bilateral ICVs was 4.66 +/- 2.28 mm (mean +/- SD), and the shape of the space could be classified as spindle, parallel, hairpin, and round types. The basal vein could be classified into well-developed, hypoplastic, hardly recognized, and mimicking two basal veins because the tributary did not join but ran parallel to the basal vein. The drainage pathways lead to the anterior or posterior portion of the vein of Galen, the ICV, the tentorial sinus, and the superior petrosal sinus. The various types of the tentorial sinus and primitive tentorial sinus which might be sacrificed during section of the tentorium were confirmed. The inferior cerebral vein draining to the tentorial sinus could be seen. 3D-CTA could also demonstrate the presence, the course, and the drainage points of the internal occipital vein, the precentral cerebellar vein, the posterior pericallosal vein, and so on. 3D-CTA is useful to evaluate the variations of the venous system and the relationship with the tumor, and for preoperative simulation and intraoperative navigation of the occipital transtentorial approach.

Epoxy-resin injection of the cerebral arterial microvasculature: An evaluation of the limits of spatial resolution in 8 Tesla MRI

The purpose of this study was to quantify the spatial resolution of microscopic arteries on magnetic resonance images acquired at 8 Tesla (T). Techniques similar to those used for standard MRI of the human brain in vivo at 8 T were utilized to generate high-resolution gradient echo (GE) images of a whole postmortem human brain whose common carotid arterial system had been injected with an epoxy-resin. Single slice images, along with summed images of up to 5 contiguous slices, were then compared to color digital photographs detailing the distribution of the arterial system on the surface of the same injected brain. There was excellent MR visualization of the microscopic cerebral arteries down to a spatial resolution of 200 microm. Through the use of an 8 T whole-body MRI scanner and standard GE imaging sequences, microscopic arterial structures can be clearly resolved down to a dimension of 200 microm.

Anatomical variations of occipital bone impressions for dural venous sinuses around the torcular Herophili, with special reference to the consideration of clinical significance

Venous blood flow through the cerebral dural sinus is variable and clinically significant. It has been investigated by cadaver dissection or radiology; however, we thought that osteology might be informative. A total of 160 dried skulls were macroscopically examined for impressions on the inner surface of the occipital bone in order to interpret the sinus flow around the torcular Herophili. The continuity between the grooves for the superior sagittal sinus (SSS) and the transverse sinuses was categorized into four types. Confluence type was noted in 56 specimens (35%), in which SSS drained into a common pool of venous sinuses. Bifurcation type was noted in 22 cases (14%), in which SSS was divided to drain into the bilateral transverse sinuses. Right dominant type was the most frequent one with 66 cases (41%), in which SSS drained only into the right transverse sinus. Left dominant type was the least frequent one with 16 cases (10%), in which SSS drained to the left, in a mirror image to the right dominant type. Clinical significance is discussed with our preliminary trial for the optimization of the inner skull surface and venous flow using computed tomography and magnetic resonance imaging, and demonstration of cerebrovascular disease.

A Biomechanical Analysis of the Causes of Traumatic Brain Injury in Infants and Children

There is significant disagreement among medical professionals regarding the mechanisms for infant brain injury. This disagreement is due in part to the failure by some to acknowledge and incorporate known biomechanical data and models into hypotheses regarding causes. A proper biomechanical understanding of the mechanisms of traumatic brain injury (TBI) challenges many published and testified assumptions regarding TBI in infants and children. This paper analyzes the biomechanical relationship between the causes of TBI in infants and children, and their physiological consequences. Loading characteristics, injury parameters and criteria, scaling, failure characteristics, differences between infants and adults, and impact due to falls are described and discussed in the context of the laws of mechanics. Recent studies are critiqued with reference to their contribution to an understanding of brain injury mechanisms. Finally, methods for improving our currently incomplete knowledge of infant head injuries, and their mechanisms, consequences and tolerances are proposed. There is an urgent need for close collaboration between physicians and biomechanicians to objectively and scientifically evaluate infant head injuries to further define their mechanical bases, and to assist in their diagnosis and treatment.

Microsurgical anatomy of the insula and the sylvian fissure

Object. The purpose of this study was to define the topographic anatomy, arterial supply, and venous drainage of the insula and sylvian fissure.

Methods. The neural, arterial, and venous anatomy of the insula and sylvian fissure were examined in 43 cerebral hemispheres.

Conclusions. The majority of gyri and sulci of the frontoparietal and temporal opercula had a constant relationship to the insular gyri and sulci and provided landmarks for approaching different parts of the insula. The most lateral lenticulostriate artery, an important landmark in insular surgery, arose 14.6 mm from the apex of the insula and penetrated the anterior perforated substance 15.3 mm medial to the limen insulae. The superior trunk of the middle cerebral artery (MCA) and its branches supplied the anterior, middle, and posterior short gyri; the anterior limiting sulcus; the short sulci; and the insular apex. The inferior trunk supplied the posterior long gyrus, inferior limiting sulcus, and limen area in most hemispheres. Both of these trunks frequently contributed to the supply of the central insular sulcus and the anterior long gyrus. The areas of insular supply of the superior and inferior trunks did not overlap. The most constant insular area of supply by the cortical MCA branches was from the prefrontal and precentral arteries that supplied the anterior and middle short gyri, respectively. The largest insular perforating arteries usually arose from the central and angular arteries and most commonly entered the posterior half of the central insular sulcus and posterior long gyrus. Insular veins drained predominantly to the deep middle cerebral vein, although frequent connections to the superficial venous system were found. Of all the insular veins, the precentral insular vein was the one that most commonly connected to the superficial sylvian vein.

Preoperative evaluation of the venous system for potential interference in the clipping of cerebral aneurysm

BACKGROUND

Variations of the venous system affecting the surgical treatment of cerebral aneurysm were evaluated using three-dimensional computed tomography angiography (3D-CTA) to evaluate the essential aspects of preoperative diagnosis.

METHODS

This study included 50 patients who underwent clipping of cerebral aneurysm through the pterional and trans-sylvan approaches. The 3D-CTA and operative findings were compared to assess the characteristics of cases in which the veins restrict brain retraction, hinder operative manipulations or require sacrifice because of the position in the operative field.

RESULTS

Superficial sylvian veins that restricted brain retraction were identified in 8 cases. The veins entered the cavernous sinus in a relatively high position just below either the sphenoid ridge (superior lateral type) or the anterior clinoid process (superior medial type), and the veins entering at a more medial position were closer to the spatula and tended to be compressed or directly excluded (superior medial type). The inferior medial type did not tend to become tense and so did not restrict brain retraction. The inferior lateral type hardly affected the operative manipulation. The first segment of the basal vein of Rosenthal, the uncal vein entering the cavernous sinus, or the sphenoparietal sinus were located in the operative field in six cases, and affected the manipulation of dissecting arteries, and exposure and clipping of the aneurysm.

CONCLUSIONS

3D-CTA provides essential information for operative planning to protect the venous system during the pterional and trans-sylvian approaches.

Estudio morfométrico mediante técnicas de imagen de la vena de Trolard en su anastomosis al seno longitudinal superior

OBJECTIVE

The main objective of this work is to allow the anatomical localization of the vein of Trolard (VT) or great anastomotic vein, before neurosurgical approaches to the parietal region.

MATERIAL AND METHODS

Thirty four patients were subjected to cerebral angiography. Measurements of different points related to the anatomy of the vein were taken in 41 studies on the lateral projection. A statistical analysis was performed.

CONCLUSIONS

The measures obtained are of practical utility to locate the final portion of the vein of Trolard in its anastomotis to the sagittal superior sinus (SLS) for planning neurosurgical approaches to the parietal region.

On the Development of the SIMon Finite Element Head Model

The SIMon (Simulated Injury Monitor) software package is being developed to advance the interpretation of injury mechanisms based on kinematic and kinetic data measured in the advanced anthropomorphic test dummy (AATD) and applying the measured dummy response to the human mathematical models imbedded in SIMon. The human finite element head model (FEHM) within the SIMon environment is presented in this paper. Three-dimensional head kinematic data in the form of either a nine accelerometer array or three linear CG head accelerations combined with three angular velocities serves as an input to the model. Three injury metrics are calculated: Cumulative strain damage measure (CSDM) - a correlate for diffuse axonal injury (DAI); Dilatational damage measure (DDM) - to estimate the potential for contusions; and Relative motion damage measure (RMDM) - a correlate for acute subdural hematoma (ASDH). During the development, the SIMon FEHM was tuned using cadaveric neutral density targets (NDT) data and further validated against the other available cadaveric NDT data and animal brain injury experiments. The hourglass control methods, integration schemes, mesh density, and contact stiffness penalty coefficient were parametrically altered to investigate their effect on the model's response. A set of numerical and physical parameters was established that allowed a satisfactory prediction of the motion of the brain with respect to the skull, when compared with the NDT data, and a proper separation of injury/no injury cases, when compared with the brain injury data. Critical limits for each brain injury metric were also established. Finally, the SIMon FEHM performance was compared against HIC15 through the use of NHTSA frontal and side impact crash test data. It was found that the injury metrics in the current SIMon model predicted injury in all cases where HIC15 was greater than 700 and several cases from the side impact test data where HIC15 was relatively small. Side impact was found to be potentially more injurious to the human brain than frontal impact due to the more severe rotational kinematics.

Scalp-recorded slow EEG responses generated in response to hemodynamic changes in the human brain

OBJECTIVE

To study whether hemodynamic changes in human brain generate scalp-EEG responses.

METHODS

Direct current EEG (DC-EEG) was recorded from 12 subjects during 5 non-invasive manipulations that affect intracranial hemodynamics by different mechanisms: bilateral jugular vein compression (JVC), head-up tilt (HUT), head-down tilt (HDT), Valsalva maneuver (VM), and Mueller maneuver (MM). DC shifts were compared to changes in cerebral blood volume (CBV) measured by near-infrared spectroscopy (NIRS).

RESULTS

DC shifts were observed during all manipulations with highest amplitudes (up to 250 microV) at the midline electrodes, and the most pronounced changes (up to 15 microV/cm) in the DC voltage gradient around vertex. In spite of inter-individual variation in both amplitude and polarity, the DC shifts were consistent and reproducible for each subject and they showed a clear temporal correlation with changes in CBV.

CONCLUSIONS

Our results indicate that hemodynamic changes in human brain are associated with marked DC shifts that cannot be accounted for by intracortical neuronal or glial currents. Instead, the data are consistent with a non-neuronal generator mechanism that is associated with the blood-brain barrier.

SIGNIFICANCE

These findings have direct implications for mechanistic interpretation of slow EEG responses in various experimental paradigms.

Surgical strategy for distal anterior cerebral artery aneurysms: microsurgical anatomy

OBJECT

Most distal anterior cerebral artery (ACA) aneurysms arise at the pericallosal-callosomarginal artery (PerA-CMA) junction, which is usually located in the A3 segment of the ACA around the genu of the corpus callosum. Aneurysms in the PerA-CMA junction are divided into two types according to their location: supracallosal and infracallosal. Infracallosal distal ACA aneurysms are defined as those located in the lower half of the A3 segment, which makes it more difficult to gain proximal control. In this study, the authors examined the microsurgical anatomy of the distal ACA region, focusing especially on the relationship between the PerA and CMA located in the lower half of the A3 (infracallosal) segment, and present a surgical strategy for dealing with distal ACA aneurysms.

METHODS

The microsurgical anatomy of the distal ACA region was examined in 22 adult cadaveric cerebral hemispheres after perfusion of the arteries and veins with colored silicone. The relationships of the infracallosal segment of the PerA to the CMA and the A2 segment of the PerA to the frontopolar artery were examined. The distance between the nasion and the site at which a parallel line directed along the long axis of the infracallosal PerA just proximal to the origin of the CMA artery crosses the forehead (which we have named the PC point) was also measured. Surgical approaches to distal ACA aneurysms were examined in stepwise dissections.

CONCLUSIONS

The PerA-CMA junctions were located in the supracallosal and infracallosal segments of A3 in 36 and 55% of cases, respectively. In the infracallosal region, it was difficult to identify the proximal PerA and to establish proximal control of the vessel. The infracallosal part of the proximal PerA coursed almost parallel to the frontal cranial base, and the PC point was 42.2 +/- 15.9 mm (mean +/- standard deviation) from the nasion. These findings indicate that there is only a limited space in which to access an infracallosal distal ACA aneurysm below the PC point and establish proximal control by the anterior interhemispheric approach. When the approach is made above the PC point, an anterior callosotomy may be necessary to establish proximal control before final aneurysm dissection and clip placement are completed. The PC point is an important surgical landmark in planning the surgical strategy for infracallosal distal ACA aneurysms.

Tentorial dural arteriovenous fistula presenting with various visual symptoms related to anterior and posterior visual pathway dysfunction: case report

OBJECTIVE AND IMPORTANCE

Dural arteriovenous fistulae (DAVFs) not directly shunting into the cavernous sinus are an infrequent cause of visual dysfunction. An unusual case of a tentorial DAVF associated with visual symptoms related to dysfunction of the anterior and posterior visual pathway is presented.

CLINICAL PRESENTATION

A 38-year-old woman with a history of long-standing bilateral proptosis experienced a sudden onset of headache and visual disturbances. Ocular examination revealed bilateral episcleral and retinal venous congestion, optic disc paleness, right superior homonymous quadrantanopsia in both eyes, and concentric narrowing of the visual field of the right eye. Angiography revealed a DAVF supplied by a falx branch arising from the left vertebral artery and both middle meningeal arteries, which drained directly into the markedly dilated vein of Galen via the basal vein of Rosenthal and the cavernous sinus into both superior ophthalmic veins.

INTERVENTION

Endovascular treatment was performed in two consecutive sessions by transarterial embolization with n-butylcyanoacrylate, which resulted in occlusion of the fistula and complete clinical cure, confirmed at the 6-month follow-up examination.

CONCLUSION

Various neuro-ophthalmological findings may be caused by an arteriovenous lesion remote from the optic organ as a result of rerouting of venous drainage compromising the visual pathway at different locations. Transarterial embolization of a DAVF may result in complete cure if advantageous arterial anatomy allows for flow control and occlusion of the fistulous connection with liquid adhesives.

Venous Infarction Resulting From Sacrifice of a Bridging Vein During Clipping of a Cerebral Aneurysm: Preoperative Evaluation Using Three-dimensional Computed Tomography Angiography-Case Report-

A 67-year-old woman presented with a ruptured aneurysm of the left internal carotid artery bifurcation. Three-dimensional computed tomography angiography (3D-CTA) demonstrated the first segment of the basal vein of Rosenthal passing in front of the internal carotid artery and the anastomosis with the cavernous sinus, the partially hypoplastic second segment, and the superficial sylvian vein entering the lateral side of the sphenoparietal sinus. Dissection of the sylvian fissure toward the distal direction enabled transfer of the superficial sylvian vein to the temporal side, but the bridging vein had to be sacrificed to secure adequate operating space. Postoperative CT demonstrated hemorrhagic infarction at the left caudate head and surrounding region. Postoperative venous infarction is not an uncommon complication of various approaches. 3D-CTA can provide important information about the venous anatomy indispensable for avoiding postoperative venous infarction.

Operative Anatomy and Classification of the Sylvian Veins for the Distal Transsylvian Approach

Methods for preservation of the sylvian veins in the transsylvian approach have not been established because of the considerable variations. This study attempted to classify the sylvian veins to facilitate systematic dissection of the sylvian fissure for sylvian veins to be preserved. The operative anatomy of the sylvian vein was examined in 82 hemispheres. The type of drainage and the pattern of branching were investigated. The superficial sylvian vein (SSV) was classified into three types according to the number of stems draining into the dural sinus on the inner surface of the sphenoid bone: The SSV was absent or hypoplastic in eight cases, the SSV was single in 38 cases, and the SSV was double in 36 cases. The SSV drained into neither the sphenoparietal sinus nor the cavernous sinus in nine cases. An anastomosis between the SSV and the deep middle cerebral vein (DMCV) was observed in 42 cases. The frontobasal bridging vein (FBBV) drained into the sphenoparietal sinus in 47 cases. The type of connection was further subdivided into four types according to the connections with the DMCV and FBBV. The venous anatomy of sylvian fissure indicates that dissection (skeletonization) of the main stem of sylvian veins from the temporal lobe should be performed to preserve the tributaries from the frontal lobe.

Transcranial ultrasonography of cerebral veins and sinuses

Transcranial ultrasonography has become a valuable diagnostic tool for the bed-side evaluation of cerebral hemodynamics. While the assessment of arterial blood flow is well established, analysis of venous hemodynamics by transcranial ultrasonography is a new application of the method. The present review summarises the current state of transcranial venous ultrasound in adults by means of transcranial Doppler (TCD) and transcranial colour-coded duplex sonography (TCCS). It gives a critical overview regarding current and possible future clinical applications of the techniques.

Occipital lobe morphological anatomy: anatomical and surgical aspects

BACKGROUND: The occipital lobe is an important region of the central nervous system and site of a wide variety of lesions. Different from others regions of the brain, whose anatomy has been already meticulously detailed, controversies about occipital lobe morphology can occasionally hinder the surgical approaches to it. METHOD: Twenty-six hemispheres were dissected, examining the distances of the medial structures of the posterior interhemispheric fissure region; identifying the sulci and gyri more frequently found in the lateral surface; and detailing the anatomy of the occipital horn of the lateral ventricle. Also, anatomical details of structures such as the calcarine sulcus and preoccipital notch were evaluated. RESULTS: Twenty-four hemispheres (92%) showed sulci with evident transverse trajectories in the lateral surfarce, and it was possible to identify marked longitudinal sulci in 16 (61%). All of the specimen presented a transverse sulcus in the inferior third of the lobe -- labeled in this paper as Inferior Transverse Occipital -- and 69% of the cases showed a transverse sulcus in the superior third -- labeled as Superior Transverse Occipital. The occipital horn was present in 53% of the cases at level of the anterior boundary of the lobe. It was a half moon shaped cavity, whose the medial wall was formed by the calcar avis and the lateral wall, roof and floor formed by fibers of the tapetum. CONCLUSION: The occipital lobe presents parameters that are often recognized in most of the dissected brain and can be useful for the planning and performance of surgery in this area of the brain.

The preservation and reconstruction of cerebral veins and sinuses

Although cerebral veins and venous sinuses are very important to the neurosurgeon, they have received adequate attention only recently. The consequences of cerebral venous occlusion are well known. When the venous outflow is compromised due to a lack of adequate collateral circulation, venous infarction follows, with swelling, haemorrhage and neuronal death. The clinical consequences will depend upon the region of involvement of the brain and the site of the infarcted tissue. The symptoms may include seizures, hemiplegia, aphasia, coma and death. Similarly, the consequences of cerebral venous sinus occlusion depend upon the availability of collateral circulation. When such collaterals are not available, papilledema and visual loss and a pseudotumour cerebri syndrome are observed in milder cases, whereas, severe diffuse brain swelling, coma and death may be observed in severe cases. Acute venous or venous sinus occlusion is potentially very dangerous, whereas slow and chronic venous or venous sinus occlusion is better tolerated. Even in such patients, some neurological manifestations may follow, when the collaterals are poor.

Subarachnoid hemorrhage caused by dural arteriovenous fistula of the sphenobasal sinus--case report

A 59-year-old woman presented with a rare middle fossa dural arteriovenous fistula (AVF) unrelated to the cavernous sinus manifesting only as subarachnoid hemorrhage. Angiography revealed shunts between the meningeal branches of both the internal and external carotid arteries and the sphenobasal sinus. The AVF drained into the superficial middle cerebral vein (SMCV) which had a varix and an anastomosis to a superior cerebral vein. The arterial supply vessels were eliminated surgically and the sinus was excised. Bleeding did not recur and there was no venous infarction. Dural AVF of the sphenoparietal sinus is associated with pulsatile exophthalmos and dural AVF of the sphenopetrosal sinus with tinnitus, but dural AVF of the sphenobasal sinus has no obvious symptom. Simple interruption of the SMCV at the penetration of the arachnoid membrane was possible because of the absence of a draining vessel to preserve AVF patency, but the arteries were eliminated in this patient to prevent formation of another AVF.

Relative positions of the arteries and veins on the dorsolateral surface of the human cerebrum

We investigated whether arteries pass superficial to veins or whether veins pass superficial to arteries at artery-vein crossings on the anterior, dorsolateral, and posterior surfaces of the human cerebrum. We examined a total of 2,266 artery-vein crossings on 40 sides of 20 cadavers. At 2,059 crossings (91%), the vein passed superficial to the artery. Thus, vein (V), artery (A), and nerve (N), if we regard the cerebrum as nerve, were generally arranged in the order VAN from the superficial to the deep layers. This concept is important for a positional understanding of blood vessels on the cerebrum and it is useful for the understanding of fluid-drainage pathways from the cerebral cortex in various pathological conditions.

Postoperative cortical venous infarction in tumours firmly adherent to the cortex

It is sometimes difficult to separate extra-axial tumours from the cortical veins in case of tumours attaching tightly to the cortex and the cortical veins. We present two patients having a postoperative cortical venous infarction. A 59 year old female had convexity meningioma above the motor cortex where abnormal cortical anastomotic veins developed. Transient hemiparesis occurred after total removal of the tumour because of venous infarction and cyst formation resulting from sacrifice of these veins which were tightly adherent to the tumour surface. A 15 year old boy with immature teratoma of the pineal region, showing several draining veins around the vascular-rich tumour, presented transient drowsiness, diplopia and partial impairment of bilateral visual acuity postoperatively because of localised cortical brain and venous damage. It is important to make an effort to preserve main cortical veins during operation as much as possible, even if the tumour adheres to the cortical surface.

[Cranioencephalic relationships between Trolard and Labbé veins: neurosurgical applications]

We accomplished an anatomic study of the anastomotic veins of Trolard and Labbé in seven human cephalic segments with the objective to accurate its stretch and references to facilitate its preservation during surgical procedure. The relationship between the Trolard vein and motor cortex was also studied.

Preservation of large bridging veins of the cranial base: technical note

OBJECTIVE

Sacrifice of a bridging vein in the cranial base occasionally may cause significant postoperative morbidity. We report a simple method for preserving large bridging veins of the cranial base by reflecting the dura when a subtemporal or transsylvian approach is used.

METHODS

In the subtemporal approach, when a larger bridging vein enters the dura attached to the bone of the temporal base before it empties into the dural sinus, the dura is dissected widely from the bone and is cut vertically toward the medial side of the temporal base in front of the entrance of the vein into the dura. The dura, which includes part of the entrance and interdural course of the vein, is reflected and retracted over the brain. In the transsylvian approach, when the bridging segment of the superficial sylvian vein becomes taut because of retraction of the temporal lobe, the dura is incised along the sphenoid ridge and is dissected and freed from the sphenoid bone.

RESULTS AND CONCLUSION

This dura-reflecting technique facilitates brain retraction without exerting tension on the bridging vein of the cranial base and is expected to help avoid injury to bridging veins during neurosurgical procedures.

Vertex epidural hematomas: imaging findings and diagnostic pitfalls

PURPOSE

Our purpose was to show the computed tomography (CT) and magnetic resonance (MR) imaging features of vertex epidural hematomas (EDHs) and emphasize pitfalls in the diagnosis of this entity.

SUBJECTS AND METHODS

The neuroradiologic studies of four patients (CT in four, MR imaging and MR venography in one) were evaluated for EDH shape, size and appearance.

RESULTS

EDHs were biconvex in three patients and crescentic in one patient. CT appearances included a collection that was hyperdense (two patients), generally isodense with a few regions of hyperdensity (one patient) and mixed hyperdense and hypodense (one patient). MR imaging findings in one patient consisted of hyperintense signal on T1-weighted images and hypointense signal on T2-weighted images. Inferior displacement of the superior sagittal sinus was seen in two patients. Diagnosis of a small vertex EDH was difficult on routine axial CT in one patient, but apparent on MR imaging and MR venography.

CONCLUSIONS

Small vertex EDHs can be difficult to diagnose on routine CT. MR imaging or thin section CT should be performed to exclude the diagnosis in patients with trauma to the skull vertex.

Cerebral microvascular architecture in the common tree shrew (Tupaia glis) revealed by plastic corrosion casts

The vascularization of the cerebrum (cerebral cortex and basal ganglia) in the common tree shrew (Tupaia glis) has been studied in detail using vinyl injection and vascular corrosion cast/SEM techniques. It is found that the arterial supply of the cerebral cortex are from cortical branches of the middle cerebral artery (MCA) and of the anterior cerebral artery (ACA). These arteries are in turn branches of the internal carotid artery (ICA). In addition, the cerebral cortex receives the blood from the cortical branches of the posterior cerebral artery (PCA) that originates from the basilar artery (BA). These cortical arteries gives rise to rectilinear orientated intracortical arteries that are divided into dense capillary networks to supply the cerebral cortex. The capillary networks drain the blood into intracortical veins and then into the tributaries of major superficial cerebral veins. The basal ganglia (caudate and lentiform nuclei) are supplied by central or perforating branches of the ACA and MCA. These central or medullary arteries give rise to arterioles that ramify into dense capillary plexuses. The venous blood from both nuclei drains into venules and finally into the tributaries of internal cerebral veins. It is obvious that on the ventral aspect, the diameter of the lateral striate artery (LSA) and of the penetrating arterioles from the MCA are much smaller than that of the MCA. These arterioles have few side branches while the peripheral branches of the superficial cerebral arteries exhibit several series of branches that are gradually reduced in diameter before branching into intracortical arteries. This could be one of the reasons why the rupture of cerebral arteries in man mostly occurs in the those originating from the ventral surface rather than from the dorsolateral surface.

Venous consideration in petrosal approach: microsurgical anatomy of the temporal bridging vein

OBJECTIVE

The technical difficulty of using the petrosal approach and the likelihood of encountering venous complications depend on the particular temporal venous anatomy. To reduce such potential risks, neurosurgeons must have adequate knowledge of the variations in the anatomy of the temporal venous drainage system, particularly of the temporal bridging veins.

METHODS

In 20 cadaveric specimens, the temporal bridging veins were examined with the aid of an operating microscope. The anatomic location of their termination and of the tributaries of these bridging veins was noted.

RESULTS

Forty-four terminations and 109 tributaries of the temporal bridging veins were identified in our specimens. The temporal bridging veins were divided into three groups according to the anatomic location of their terminations: 1) the transverse sinus group (seen in all 20 hemispheres), with drainage into the lateral part of the cerebellar tentorium, to which most of the vein of Labbé belongs; 2) the tentorial group (seen in 50% of the 20 hemispheres), with drainage into the medial part of the tentorium, which is composed mainly of the middle and posterior temporobasal veins; and 3) the petrosal group (seen in 55% of the 20 hemispheres), with entry around the superior petrosal sinus, which may limit mobility of the temporal lobe in the petrosal approach. On the basis of this anatomic information, we propose a new classification of the temporal venous drainage system and discuss the clinical implications of these findings.

CONCLUSION

In planning the petrosal approach, great care should be taken not only with the vein of Labbé but also with the petrosal bridging veins. Knowledge of this venous anatomy can reduce venous complications during the lateral cranial base approach.