Feeding artery pressure and venous drainage pattern are primary determinants of hemorrhage from cerebral arteriovenous malformations

[Cerebral arteriovenous malformations: evaluation of the hemorrhagic risk and its morbidity]

Evaluation of the hemorrhagic risk associated with intracranial arteriovenous malformation is a keypoint question for physicians involved in the management of these patients. Indeed, this hemorrhagic risk including its morbid-mortality consequences has to be balanced with the therapeutic risk. All the published studies have estimated the annual bleeding risk between 2 to 4%; a first hemorrhagic event is associated with an increased risk of a new bleeding. Mortality associated with AVM bleeding is estimated between 10 to 15%, with a 50% risk of morbidity. Factors associated with an increased risk of bleeding include existence of aneurysms (intranidal or flow related pedicular, proximal or distal) and some venous drainage patterns such as deep venous drainage or venous stenosis.

Natural history, evaluation, and management of intracranial vascular malformations

Intracranial vascular malformations are seen increasingly in clinical practice, primarily because of advances in cross-sectional brain and spinal cord imaging. Commonly encountered lesion types include arteriovenous malformations, cavernous malformations, venous malformations, dural arteriovenous fistulas, and capillary telangiectasias. Patients can experience various symptoms and signs at presentation. The natural history of vascular malformations depends on lesion type, location, size, and overall hemodynamics. The natural history for each lesion subtype is reviewed, with special consideration of the risk of hemorrhage or other adverse outcomes after the lesion is detected and any known predictors of hemorrhage or other outcomes. In practice, these data are compared with the risk of available treatment options as the optimal management is clarified. A multidisciplinary approach including neurosurgery, radiosurgery, interventional neuroradiology, and vascular neurology is most useful in determining the best management strategy.

Endovascular Pressure Measurements: Validation with a Pulsatile Flow Model and Haemodynamic Assessment of Brain AVMs

SUMMARY

Intravascular pressure measurements for several types of endovascular catheters were obtained in an in vitro model to validate the pressure readings obtained during the interventional procedures of brain AVM embolization. An experimental model was used where the beat rate, flow and pressures were as close as possible to the average human values of interest. It is shown that the corrections increase with the decreasing inner diameter of the catheter used and with increasing vascular pressure. We have also shown that there were no differences between measurements made with the catheter in the direction of flow or against it. An average pressure reading corrections for the various microcatheters to compensate the readings obtained during in vivo monitoring is presented. The haemodynamic assessment of 81 brain AVMs was performed using the endovascular measurement of arterial pressure in 389 feeding arteries during embolization. Mostly, the feeders' arterial median pressure was half the systemic arterial pressure but there was a wide variability of AV shunts in brain AVMs not only from one brain AVM to another but also within the same brain AVM. Measurement of arterial feeder pressure is an inexpensive, quick and accurate tool to evaluate the type of AV shunts within brain AVM.

Do the morphological characteristics of arteriovenous malformations affect the results of radiosurgery?

OBJECT

The authors sought to determine which morphological features of arteriovenous malformations (AVMs) are statistically predictive of preradiosurgical hemorrhage, postradiosurgical hemorrhage, and neuroimaging-defined failure of radiosurgical treatment. In addition, correlation between computerized tomography (CT) scanning and angiography for the identification of AVM structures was investigated.

METHODS

Archived CT dosimetry and available angiographic and clinical data for 268 patients in whom AVMs were treated with linear accelerator radiosurgery were retrospectively reviewed. Many of the morphological features of AVMs, including location, volume, compact or diffuse nidus, neovascularity, ease of nidus identification, number of feeding arteries, location (deep or superficial) of feeding arteries, number of draining veins, deep or superficial venous drainage, venous stenoses, venous ectasias, and the presence of intranidal aneurysms, were analyzed. In addition, a number of patient and treatment factors, including patient age, presenting symptoms, radiation dose, repeated treatment, and radiological outcome, were subjected to multivariate analyses. Two hundred twenty-seven patients were treated with radiosurgery for the first time and 41 patients underwent repeated radiosurgery. Eighty-one patients presented with a history of AVM hemorrhage and 91 patients had AVMs in a periventricular location. Twenty-six patients (10%) experienced a hemorrhage following radiosurgery. Of the 268 patients, 81 (30%) experienced angiographically defined cures, and 37 (14%) experienced MR imaging-defined cures. Eighty-six patients (32%) experienced neuroimaging-defined treatment failure, and 64 underwent insufficiently long follow up. A larger AVM volume (odds ratio [OR] 0.349; p = 0.004) was associated with a decreased rate of pretreatment hemorrhage, whereas periventricular location (OR 6.358; p = 0.000) was associated with an increased rate of pretreatment hemorrhage. None of the analyzed factors was predictive of hemorrhage following radiosurgery. A higher radiosurgical dose was strongly correlated with neuroimaging-defined success (OR 3.743; p = 0.006), whereas a diffuse nidus structure (OR 0.246; p = 0.008) and associated neovascularity (OR 0.428; p = 0.048) were each associated with a lower neuroimaging-defined cure rate. A strong correlation between CT scanning and angiography was noted for both nidus structure (p = 0.000; Fisher exact test) and neovascularity (p = 0.002; Fisher exact test).

CONCLUSIONS

Patients presenting with AVMs that are small or periventricular were at higher risk for experiencing hemorrhage. A higher radiosurgical dose correlated strongly with neuroimaging-defined success. Patients in whom the AVM had a diffuse structure or associated neovascularity were at higher risk for neuroimaging-defined failure of radiosurgery. A strong correlation between CT scanning and angiography in the assessment of AVM structure was demonstrated.

Intraoperative Doppler to Measure Cerebrovascular Resistance as a Guide to Complete Resection of Arteriovenous Malformations

OBJECTIVE:

Intraoperative color Doppler ultrasound has been used to locate arteriovenous malformations (AVMs). We describe the use of spectral Doppler to measure flow resistance and resistive index (RI) of vessels around the nidus to distinguish feeding arteries from en passant and normal vessels. This is particularly helpful in small AVMs and aids in the identification of normal vessels and completeness of resection by ruling out persistent low RI flow.

METHODS:

Seven patients with AVMs underwent resection. Spectral Doppler applied to the vessels in proximity to the AVM, along with calculated RI, was used to identify feeding arteries and draining veins. After presumed surgical resection of the AVM, pre-resection and postresection RIs were compared to identify residual AVM. Postoperative angiography was performed in all seven patients to confirm complete resection of the AVM.

RESULTS:

The mean pre-resection RI of vessels feeding the AVM was 0.34 (±0.01). In five patients without residual nidus on the basis of postresection color Doppler and postoperative angiogram, the postresection RI was 0.62 (±0.04). In two patients, the postresection scan identified a nidus with persistent low RI flow. Once residual AVM was resected, the RI became significantly higher. A postoperative angiogram confirmed complete resection of the AVM in all patients.

CONCLUSION:

Intraoperative duplex Doppler allowed more accurate localization of the AVM nidus. RI of the vessels around the AVM helped to distinguish vessels feeding the AVM from en passant vessels. Furthermore, comparison of pre-resection and postresection RI accurately indicated the completeness of resection.

THE RELATIONSHIP OF COEXISTING EXTRANIDAL ANEURYSMS TO INTRACRANIAL HEMORRHAGE IN PATIENTS HARBORING BRAIN ARTERIOVENOUS MALFORMATIONS

OBJECTIVE

We hypothesized that coexisting extranidal arterial aneurysms (EAs) would be associated with an increased risk of incident intracranial hemorrhage (ICH) from brain arteriovenous malformation (BAVM) rupture.

METHODS

To determine the presence of EAs and compare the sources and locations of ICH, we retrospectively reviewed the computed tomographic, magnetic resonance imaging, and angiographic studies of patients who presented between 1990 and 1999. EAs were defined as saccular luminal dilations of the parent feeding vessels that were proximally flow-related (i.e., at the circle of Willis), distally flow-related (i.e., distal to the circle of Willis), and unrelated (i.e., in circulation distant from the BAVM).

RESULTS

Of 314 BAVM patients, 138 (44%) presented with ICH. In the ICH group, 22 patients (16%) had aneurysmal ICH, 100 (72%) had BAVM ICH, and 16 (12%) had ICH from an indeterminate source. There were 61 patients with 1 or more EAs (29 patients with 42 flow-related proximal aneurysms, 39 patients with 48 flow-related distal aneurysms, and 10 patients with 20 unrelated aneurysms). Multivariate regression analysis revealed that ICH patients were more likely than non-ICH patients to have a coexisting EA (35 versus 13%; odds ratio = 3.9; 95% confidence interval, 2.1-7.5; P < 0.001), but this effect was not present when only BAVM-related ICH was considered (odds ratio = 0.3; 95% confidence interval, 0.1-1.0; P = 0.052). Other independent predictors of ICH included small AVM size (<3 cm), exclusively deep venous drainage, and the presence of an intranidal aneurysm.

CONCLUSION

Clinical presentation with ICH was associated with EA aneurysms, but the association was due to aneurysmal rather than BAVM rupture, suggesting that EAs and the BAVM ICH risks may be considered as separate entities in future studies.

Management of patients with brain arteriovenous malformations

Arteriovenous malformations (AVMs) of the brain, which are probably genetically determined, are errors in the development of the vasculature that, together with the effects of blood flow, may lead to a focal arteriovenous shunt. Clinically, the adult patient may present with acute or chronic neurological symptoms-fixed or unstable-such as deficits, seizures or headache. Sometimes the lesion is an incidental finding. In about half of the patients, the revealing event is an intracranial haemorrhage. The prevalence of AVM in the western world is probably <0.01% and the detection rate is about one per 100,000 person-years. Most AVMs are revealed in patients 20-40 years of age. Therefore, the risk of developing neurological symptoms from an AVM, usually because of haemorrhage, increases with patient age. In the young adult population, AVMs are significant risk factors for hemorrhagic stroke. This risk increases with AVM volume and is higher in centrally located AVMs. Almost all patients with AVM are subjected to treatment, either by surgery, radiosurgery or embolisation, with the functional aim of reducing the risk of haemorrhage or to alleviate neurological symptoms with an acceptable treatment risk. Few neurocentres have physicians highly skilled in all treatment modalities. Therefore, the prescribed treatment may not be defined from an objective assessment of what is optimal for each individual patient, but rather from local expertise. In this context, more and better data about the natural history and the outcome of different treatments, as well as predictive models, would be valuable to help to optimise the management. Management strategies obviously differ according to local preferences, but results presented in the literature suggest the following strategy: (I) cortically located AVMs with a nidus volume <10 ml could be operated, with or without presurgical embolisation, unless there is a single feeder that can easily be catheterised and embolised for obliteration or other obvious target for embolisation, such as pseudoaneurysms or large fistulae; (II) centrally located AVMs with a nidus volume <10 ml should be treated by radiosurgery, unless suitable for embolisation as indicated above; (III) patients harbouring AVMs with a nidus volume >10 ml could benefit from targeted partial embolisation followed by radiosurgery or surgery, depending on the angioarchitecture; and (IV) AVMs >20 ml nidus volume usually have a high treatment risk with any treatment modality and are not obvious targets for treatment at all.

Deep arteriovenous malformations of the basal ganglia and thalamus: natural history

OBJECT

Patients with arteriovenous malformations (AVMs) in a deep location and with deep venous drainage are thought to be at higher risk for hemorrhage than those with AVMs in other locations. Despite this, the natural history of AVMs of the basal ganglia and thalamus has not been well studied.

METHODS

The authors retrospectively evaluated a cohort of 96 patients with AVMs in the basal ganglia and thalamus with respect to the tendency of these lesions to hemorrhage between the time of detection and their eventual successful management. The 96 patients studied had a mean age of 22.7 years at diagnosis, and 51% were male. Intracranial hemorrhage (ICH) was the event leading to clinical detection in 69 patients (71.9%), and 85.5% of these patients were left with hemiparesis. After diagnosis, 25 patients bled a total of 49 times. The cumulative clinical follow up after detection but before surgical management was 500.2 patient-years. The risk of hemorrhage after detection of an AVM of the basal ganglia or thalamus was 9.8% per patient-year.

CONCLUSIONS

The rate of ICH in patients with AVMs of the basal ganglia or thalamus (9.8%/year) is much higher than the rate in patients with AVMs in other locations (2-4%/year). The risk of incurring a neurological deficit with each hemorrhagic event is high. Treatment of these patients at specialized centers is recommended to prevent neurological injury from a spontaneous ICH.

Intention-to-treat analysis of Spetzler-Martin grades IV and V arteriovenous malformations: natural history and treatment paradigm

OBJECT

In this study the authors quantified a subgroup of patients with Spetzler-Martin Grades IV and V arteriovenous malformations (AVMs) recommended for complete, partial, or no treatment, and calculated the retrospective hemorrhage rate for these lesions.

METHODS

Between July 1997 and May 2000, 73 consecutive patients with Grades IV and V AVMs were evaluated prospectively by the cerebrovascular team at Barrow Neurological Institute. Treatment recommendations given to the patients or referring physicians were classified as complete treatment, partial treatment, and no treatment. Retrospectively, the hemorrhage rates associated with these treatment groups were also calculated. In the prospective portion of the study (the intention-to-treat analysis), no treatment of the AVM, was recommended for 55 patients (75%) and partial treatment was recommended for seven patients (10%). Aneurysms associated with an AVM were obliterated by surgical or endovascular treatment in seven patients (10%), and complete surgical removal was recommended for four patients (5%). The overall hemorrhage rate for Grades IV and V AVMs was 1.5% per year. The annual risk of hemorrhage was 10.4% among patients who previously had received incomplete treatment, compared with patients without previous treatment.

CONCLUSIONS

The hemorrhage risk of 1.5% per year, which was associated with Grades IV and V AVMs appears to be lower than that reported for Grades I through III AVMs. The authors recommend that no treatment be given for most Grades IV and V AVMs. No evidence indicates that partial treatment of an AVM reduces a patient's risk of hemorrhage. In fact, partial treatment may worsen the natural history of an AVM. The authors do not support palliative treatment of AVMs, except in the specific circumstances of arterial or intranidal aneurysms or progressive neurological deficits related to vascular steal. Complete treatment is warranted for patients with progressive neurological deficits caused by hemorrhage of the AVM. This selection process plays a significant role in the relatively low combined morbidity and mortality rates for Grade IV and Grade V AVMs (17 and 22%, respectively) reported by the cerebrovascular group in both retrospective and prospective studies.

Trigeminal neuralgia caused by microarteriovenous malformations of the trigeminal nerve root entry zone: symptomatic relief following complete excision of the lesion with nerve root preservation

OBJECT

Within a series of 341 consecutive patients who underwent posterior fossa surgery for trigeminal neuralgia (TN), in five the cause was found to be a microarteriovenous malformation (micro-AVM) located in the region of the trigeminal nerve root entry zone (REZ). The surgical management and clinical outcomes of these cases are presented.

METHODS

Patients were identified from a prospectively collected database of all cases of TN treated at one institution between 1980 and 2000. Presentation was clinically indistinguishable from TN caused by vascular compression. Preoperative imaging, including computerized tomography scanning (two cases) and magnetic resonance (MR) imaging and MR angiography (three cases), failed to demonstrate an AVM except for one case in which multiple abnormal vessels were identified in the trigeminal REZ on an MR image obtained using a 1.5-tesla magnet. All patients underwent a standard retromastoid craniotomy. In all cases a small AVM embedded in the trigeminal REZ was identified and completely excised, with preservation of the trigeminal nerve. All patients experienced immediate relief of pain following surgery. Postoperatively, in one patient a small pontine hematoma developed, resulting in permanent trigeminal nerve anesthesia in the V2 and V3 divisions. All patients were free from pain at a mean follow-up period of 30 months.

CONCLUSIONS

These rare lesions are usually angiographically occult, but may sometimes be identifiable on high-resolution MR images. Total microsurgical resection with nerve preservation is possible, although operative complications are relatively common, reflecting the intimate association between these lesions and the pons. Complete resection is advised not only for symptom relief, but also to eliminate the theoretical risk of pontine hemorrhage.

Concurrent arterial aneurysms in brain arteriovenous malformations with haemorrhagic presentation

OBJECTIVE

To assess the effect of concurrent arterial aneurysms on the risk of incident haemorrhage from brain arteriovenous malformations (AVMs).

METHODS

In a cross sectional study, 463 consecutive, prospectively enrolled patients from the Columbia AVM Databank were analysed. Concurrent arterial aneurysms on brain angiography were classified as feeding artery aneurysms, intranidal aneurysms, and aneurysms unrelated to blood flow to the AVM. Clinical presentation (diagnostic event) was categorised as intracranial haemorrhage proved by imaging or non-haemorrhagic presentation. Univariate and multivariate statistical models were applied to test the effect of age, sex, AVM size, venous drainage pattern, and the three types of aneurysms on the risk of AVM haemorrhage at initial presentation.

RESULTS

Arterial aneurysms were found in 117 (25%) patients with AVM (54 had feeding artery aneurysms, 21 had intranidal aneurysms, 18 had unrelated aneurysms, and 24 had more than one aneurysm type). Intracranial haemorrhage was the presenting symptom in 204 (44%) patients with AVM. In the univariate model, the relative risk for haemorrhagic AVM presentation was 2.28 (95% confidence interval (CI) 1.12 to 4.64) for patients with intranidal aneurysms and 1.88 (95% CI 1.14 to 3.08) for those with feeding artery aneurysms. In the multivariate model an independent effect of feeding artery aneurysms (odds ratio 2.11, 95% CI 1.18 to 3.78) on haemorrhagic AVM presentation was found. No significant effect was seen for intranidal and unrelated aneurysms. The attributable risk of feeding artery aneurysms for incident haemorrhage in patients with AVM was 6% (95% CI 1% to 11%).

CONCLUSIONS

The findings suggest that feeding artery aneurysms are an independent determinant for increased risk of incident AVM haemorrhage.

Relationship of nidal vessel radius and wall thickness to brain arteriovenous malformation hemorrhage

Cerebral (brain) arteriovenous malformations (BAVMs) are a tangle of disorganized vessels that are a rare cause of hemorrhagic stroke in the general population. Although clinical presentation of hemorrhage may be related to the structure of BAVM vessels, there has been no systematic quantitative analysis of BAVM vessel morphology. Histological sections of excised BAVM lesions were prepared from patients who presented with hemorrhage (n = 14) and from patients with no history of hemorrhage (n = 22). Mean values of radius and wall thickness in each section were determined. BAVM radii were 422+/-136 microm (mean +/- SD), minimum wall thickness (thinnest portion of the wall) was 54+/-14 microm; and the minimum thickness/radius ratio was 0.23+/-0.07. Greater vessel wall thickness was associated with hemorrhagic presentation (OR= 1.1; p = 0.046) after adjusting for feeding artery pressure. Because BAVM vessels from patients presenting with hemorrhage had thicker vessel walls, the search for structural properties predisposing BAVM rupture should be expanded beyond the morphological properties analyzed here.

Arteriovenous malformations

Arteriovenous malformations of the brain are congenital vascular lesions that affect 0.01-0.50% of the population, and are generally present in patients aged 20-40 years. The usual clinical presentations are haemorrhage, seizures, progressive neurological deficit, or headache. Results of natural history studies have shown a yearly haemorrhage rate of 1-4%. Frequency of rebleeding has increased over the years, and several factors that increase risk of haemorrhage have been identified. Although substantial, the morbidity associated with haemorrhages could be less than previously thought. Over the past decade, great advances have been made in application of endovascular embolisation techniques, stereotactic radiosurgery, and microsurgery, allowing effective multidisciplinary treatment of arteriovenous malformations, including those previously deemed to be untreatable. Increasing attention has been paid to management of flow-related aneurysms associated with these malformations. Finally, many reports of recurrent arteriovenous malformations have coincided with new theories regarding the embryogenesis of these disorders and laboratory work suggesting their proliferative potential.

Adaptation of cerebral circulation to brain arteriovenous malformations increases feeding artery pressure and decreases regional hypotension

PURPOSE

To determine how the adaptation of extranidal cerebral vessels affects feeding artery pressure, draining vein pressure, and regional hypotension due to the presence of brain arteriovenous malformations (BAVMs).

CONCEPT

BAVMs cause high flows in feeding arteries and draining veins and can induce profound hypotension in the neighboring vasculature. Despite the large difference in flow, endothelial shear stress (tau) observed in vessels ipsilateral to the BAVM is similar to tau in vessels contralateral to the BAVM, suggesting that the conductance vessels successfully adapt to keep tau constant. However, because BAVMs are discovered only after they are well developed, the natural history of the adaptation process in extranidal vessels is unknown.

RATIONALE

Currently, no way exists to determine experimentally the effects of adaptation of extranidal vessels in human patients. Therefore, a mathematical model of the cerebral vasculature is used to study adaptation in response to BAVMs. By comparing pressures and flows calculated before and after adaptation, the effect of adaptation of the conductance vessels on regional hemodynamics can be evaluated.

DISCUSSION

Structural adaptation of the extranidal circulation seems not only to reset tau, but also to ameliorate regional hypotension induced by BAVMs. However, this compensatory mechanism also increases feeding artery pressure and thus may increase the risk of hemorrhagic stroke.

Functional evaluation of arteriovenous malformations

Detailed knowledge of the angioarchitecture of arteriovenous malformations (AVMs) is necessary in determining the optimal timing and method of treatment of these challenging lesions. Many techniques are available for studying the functionality of surrounding cortical structures of AVMs. These include the use of positron emission tomography, functional magnetic resonance imaging, magnetoencephalography, and direct provocative testing of cortical function. The use of these methods to determine flow dynamics and tissue perfusion is also reviewed. These techniques are discussed in the present study, and their judicious utilization will enhance the safety of AVM therapy.

Epidemiology and natural history of arteriovenous malformations

The epidemiology and natural history of cerebral arteriovenous malformations (AVMs) remains incompletely elucidated. Several factors are responsible. With regard to the incidence and prevalence of AVMs, the results of prior studies have suffered because of the retrospective design, the use of nonspecific ICD-9 codes, and a focus on small genetically isolated populations. Recent data from the New York Islands AVM Hemorrhage Study, an ongoing, prospective, population-based survey determining the incidence of AVM-related hemorrhage and the associated rates of morbidity and mortality in a zip code–defined population of 10 million people, suggests that the AVM detection rate is 1.21/100,000 person-years (95% confidence interval [CI] 1.02–1.42) and the incidence of AVM-hemorrhage is 0.42/100,000 person-years (95% CI 0.32–0.55). Contemporaneous data from the Northern Manhattan Stroke Study, a prospective, longitudinal population-based study of nearly 150,000 patients in which the focus is to define the incidence of stroke, suggest the crude incidence for first-ever AVM-related hemorrhage to be 0.55/100,000 person-years (95% CI 0.11–1.61). Efforts are ongoing to study the natural history of both ruptured and unruptured AVMs in these datasets to examine the relevance of prior studies of patients selected for conservative follow up in Finland. In addition, data are being gathered to determine whether risk factors for future hemorrhage, which have previously been established in small case series, are valid when applied to whole populations. Together, these data should help inform therapeutic decisionmaking.

Anesthesia-related considerations for cerebral arteriovenous malformations

In the optimum anesthetic management of patients with cerebral arteriovenous malformations (AVMs), the anesthesiologist should be familiar with the general pathophysiology of these lesions and various strategies for treatment. In this review, the authors outline these issues with special attention to cerebral hemodynamic changes induced by AVMs and their resection.

Evidence of increased endothelial cell turnover in brain arteriovenous malformations

OBJECTIVE

We hypothesized that human brain arteriovenous malformations (BAVMs) are nonstatic vascular lesions with active angiogenesis or vascular remodeling. To test this hypothesis, we assessed endothelial cell turnover in BAVMs.

METHODS

We identified nonresting endothelial cells by use of immunohistochemistry for the Ki-67 antigen. From archived paraffin blocks, we selected BAVM vessels without intravascular thrombosis or embolic material in areas nonadjacent to the nidus edge. For controls, we used 50- to 100-microm diameter cortical vessels from temporal lobe cortex removed for epilepsy treatment. The Ki-67 index was calculated as a percentage of Ki-67-positive endothelial cells. The data were analyzed by the nonparametric Mann-Whitney test and reported as mean +/- standard deviation.

RESULTS

Thirty-seven specimens that met the above criteria were selected. There were 26 +/- 15 vessels counted in each BAVM specimen versus 18 +/- 5 in each control cortex (n = 5). The mean Ki-67 index was higher for BAVM vessels than control cortical vessels (0.7 +/- 0.6 versus 0.1 +/- 0.2%; P = 0.005), which represented an approximately seven-fold increase in the number of nonresting endothelial cells. In the BAVM group, there was a trend for younger patients to have a wider variation and higher Ki-67 index than older patients; no trend was evident in the control group.

CONCLUSION

Compared with control vessels, BAVM vessels have higher endothelial cell turnover, which suggests the presence of active angiogenesis or vascular remodeling in BAVMs.

Haemodynamics of arteriovenous malformations of the brain and consequences of resection: a review

The physiological manifestations of arteriovenous fistulae in humans have been studied since the 18th century. However, confusion regarding concepts of cerebral 'steal', 'normal perfusion breakthrough', and 'congestive hyperaemia' continue. Although the advent of more accurate monitoring of pressures and flows within the brain has provided useful information to help understand some of these proposed pathological hypotheses, disagreement still exists. The purpose of this review is to examine the current physiological data in attempt to explain the clinicopathological manifestations of arteriovenous malformations of the brain and the consequences of their removal.

Anaesthesia for interventional neuroradiology

Neuroradiologists have extended their treatment modalities in the field of vascular neurosurgery. The rapidly emerging and re-engineered neuroradiological techniques confront the anaesthetist with an increasing number of patients with severe neurological disease. More of these patients will need general anaesthesia in order to facilitate the endovascular procedure, including catheter placement, deposition of embolic material, and improved imaging. Anaesthetists are challenged by additional anaesthesiological aspects previously not encountered in neuroanaesthesia. A safe anaesthetic management is based on a broad understanding of pathophysiological and technical issues that arise with the endovascular treatment of cerebral vasculopathy.

The epidemiology of brain arteriovenous malformations

OBJECTIVE

Common estimates of the prevalence rate for pial arteriovenous malformations (AVMs) of the brain vary widely, and their accuracy is questionable. Our objective was to critically review the original sources from which these rates were derived and to establish best estimates for both the incidence and prevalence of the disease.

METHODS

We reviewed all of the relevant original literature: autopsy series, the Cooperative Study of Intracranial Aneurysms and Subarachnoid Hemorrhage and related analyses, and other population-based studies. We also modeled the confidence intervals of estimates for a process of low prevalence such as AVMs.

RESULTS

Many of the prevalence estimates (500-600/100,000 population) were based on autopsy data, a source that is inherently biased. Other estimates (140/100,000 population) originated from an inappropriate analysis of data from the Cooperative Study. The most reliable information comes from a population-based study of Olmsted County, MN, but prevalence data specific to AVMs was not found in that study.

CONCLUSION

The estimates for AVM prevalence that are published in the medical literature are unfounded. Because of the rarity of the disease and the existence of asymptomatic patients, establishing a true prevalence rate is not feasible. Owing to variation in the detection rate of asymptomatic AVMs, the most reliable estimate for the occurrence of the disease is the detection rate for symptomatic lesions: 0.94 per 100,000 person-years (95% confidence interval, 0.57-1.30/100,000 person-years). This figure is derived from a single population-based study, but it is supported by a reanalysis of other data sources. The prevalence of detected, active (at risk) AVM disease is unknown, but it can be inferred from incidence data to be lower than 10.3 per 100,000 population.

New concepts in adult brain arteriovenous malformations

Brain arteriovenous malformations are currently attracting increasing attention among clinicians as modern brain imaging techniques facilitate both diagnostic and follow-up evaluation. Their frequent presentation in young individuals, at times with flagrant clinical effects caused by cerebral hemorrhages or seizure disorders, keeps clinicians alert to any improvement in treatment strategies. Recent technical advances in surgical, endovascular, and radiation therapy add to the constantly accumulating data on clinical features, natural course, and treatment outcome in adult arteriovenous malformation patients. This review focuses on new concepts in arteriovenous malformation etiology, classification, treatment, and study approaches.

Imaging and interventional neuroradiology

Technical innovations in neuroimaging have improved diagnosis and prognosis, whereas developments in interventional neuroradiology have extended the range of therapy to different patient populations. These changes in service demand the identification of those clinical and technical factors distinguishing feasibility from futility, in order to increase population efficiency and reduce the harm associated with inappropriate therapy.

What determines the risk of hemorrhage from cerebral arteriovenous malformations?

We reviewed seven recent articles that discuss the risk factors associated with the hemorrhagic presentation of cerebral arteriovenous malformations (AVMs). Although several such factors have been identified, only nine have been shown to be independent predictors of AVM hemorrhage by multiple logistic regression. All of the studies reviewed are subject to biases that compromise their ability to identify risk factors for hemorrhage confidently. A prospective, multicenter, controlled trial would be necessary to identify such risk factors with certainty.

Theoretical modelling of arteriovenous malformation rupture risk: a feasibility and validation study

PURPOSE

To explore the feasibility of using a theoretical computational model to simulate the risk of spontaneous arteriovenous malformation (AVM) haemorrhage.

METHODS

Data from 12 patients were collected from a prospective databank which documented the angioarchitecture and morphological characteristics of the AVM and the feeding mean arterial pressure (FMAP) measured during initial superselective angiography prior to any treatment. Using the data, a computational model of the cerebral circulation and the AVM was constructed for each patient (patient-specific model). Two model risk (Risk(model)) calculations (haemodynamic- and structural-weighted estimates) were performed by using the patient-specific models. In our previously developed method of haemodynamic-weighted estimate, Risk(model) was calculated with the simulated intranidal pressures related to its maximal and minimal values. In the method of structural-weighted estimate developed and described in this paper, the vessel mechanical properties and probability calculation were considered in more detail than in the haemodynamic-weighted estimate. Risk(model) was then compared to experimentally determined risk which was calculated using a statistical method for determining the relative risk of having initially presented with AVM haemorrhage, termed Risk(exp).

RESULTS

The Risk(model) calculated by both haemodynamic- and structural-weighted estimates correlated with experimental risks with chi2 = 6.0 and 0.64, respectively. The risks of the structural-weighted estimate were more correlated to experimental risks.

CONCLUSIONS

Using two different approaches to the calculation of AVM haemorrhage risk, we found a general agreement with independent statistical estimates of haemorrhagic risk based on patient data. Computational approaches are feasible; future work can focus on specific pathomechanistic questions. Detailed patient-specific computational models can also be developed as an adjunct to individual patient risk assessment for risk-stratification purposes.