Hemodynamic and metabolic effects of cerebral arteriovenous malformations studied by positron emission tomography

Comparative analysis of peri-nidal cerebral blood flow and metabolism using a novel quantitative 15O-PET method in patients with arteriovenous malformations

To effectively treat cerebral arteriovenous malformations (AVMs), peri-nidal flow regulation and metabolic status must be understood. In this study, we used 15O-oxygen positron emission tomography (PET) post-processing analysis to investigate vascular radioactivity in the nidal region of AVMs. Single-dynamic PET imaging was performed on seven unruptured AVM patients during the sequential inhalation of 15O2 and C15O2. A previously validated dual-tracer basis function method (DBFM) was employed to calculate parametric images. The results of our study were as follows. First, in remote and contralateral AVM regions, DBFM and a previous approach of dual-tracer autoradiography (DARG) showed strong positive correlations in cerebral blood flow (CBF), cerebral oxygen metabolism rate (CMRO2), and oxygen extraction fraction. Second, peri-nidal CBF and CMRO2 correlation was lower, and overestimation occurred with DARG compared to with DBFM. Third, on comparing DBFM to quantitative 123I-iodoamphetamine single-photon emission computed tomography (SPECT), CBF correlated significantly. In contrast, the correlation between DARG and quantitative 123I-iodoamphetamine-SPECT was weaker in the peri-nidal regions. Fourth, analysis of tissue time-activity curves demonstrated good reproducibility using the novel formulation in the control, peri-nidus, and core nidal regions, indicating the adequacy of this approach. Overall, the DBFM approach holds promise for assessing haemodynamic alterations in patients with AVMs.

Feasibility of Flat Panel Detector CT in Perfusion Assessment of Brain Arteriovenous Malformations: Initial Clinical Experience

The different results from flat panel detector CT in various pathologies have provoked some discussion. Our aim was to assess the role of flat panel detector CT in brain arteriovenous malformations, which has not yet been assessed. Five patients with brain arteriovenous malformations were studied with flat panel detector CT, DSC-MR imaging, and vessel-encoded pseudocontinuous arterial spin-labeling. In glomerular brain arteriovenous malformations, perfusion was highest next to the brain arteriovenous malformation with decreasing values with increasing distance from the lesion. An inverse tendency was observed in the proliferative brain arteriovenous malformation. Flat panel detector CT, originally thought to measure blood volume, correlated more closely with arterial spin-labeling-CBF and DSC-CBF than with DSC-CBV. We conclude that flat panel detector CT perfusion depends on the time point chosen for data collection, which is triggered too early in these patients (ie, when contrast agent appears in the superior sagittal sinus after rapid shunting through the brain arteriovenous malformation). This finding, in combination with high data variability, makes flat panel detector CT inappropriate for perfusion assessment in brain arteriovenous malformations.

[The efficacy of remaxol addition in the treatment of alcohol withdrawal syndrome]

OBJECTIVE

To study the efficacy of remaxol addition in the treatment scheme of alcohol withdrawal syndrome.

MATERIAL AND METHODS

Eighty patients with alcohol dependence and physical symptoms of alcohol withdrawal syndrome were enrolled. All patients received basic therapy in accordance to the applicable standards of treatment. The patients were randomized to remaxol introduced intravenously 2 times a day (morning and afternoon) in dose of 400 ml for 7 days (n=40) and saline with 25%-magnesium sulfate (10 ml) and 4% potassium chloride (10 ml) (n=40).

RESULTS

The effectiveness of the inclusion of remaxol was expressed in a more rapid relief of asthenic syndrome, reduction of phenomena such as tension, dysphoria, headache and impaired coordination of samples. Patients treated with remaxol demonstrated a trend towards a more rapid reduction of the affective (p=0.08) and behavioral components (p=0.09) of the syndrome of pathological craving for alcohol. Hepatoprotective and detoxification properties of the drug were confirmed by the significant decline in ALT and AST activity to the 20th day of treatment. Significant positive changes in lipid metabolism (HDL to the 7th day of treatment) and a normalizing effect on the processes of tissue respiration were shown as well. No adverse effects were noted.

CONCLUSION

The data obtained allow to recommend the inclusion of remaxol in the complex treatment regimens of alcohol withdrawal syndrome to improve the treatment efficacy.

Normal pressure perfusion breakthrough after resection of arteriovenous malformation

Objectives. The syndrome of normal pressure perfusion breakthrough (NPPB) follows the surgical resection of a small fraction of cerebral arteriovenous malformations (AVM). Although intraoperative hyperemia occurs in NPPB, the relationship and temporal profile of vasomotor paralysis to NPPB are unknown. In the present study, serial transcranial Doppler (TCD) studies (static and stress) were correlated with clinic observations to determine the relationship and temporal profile of vasomotor paralysis to NPPB. Methods. Thirty-five patients underwent complete AVM removal with preservation of the normal arteries and veins. Serial TCD examinations were performed under static and stress conditions (CO(2), Diamox, or blood pressure challenge). Vasomotor paralysis was considered present when CO(2) or Diamox challenge produced less than a 10% change in flow velocity or when flow velocity changed with blood pressure over physiological ranges. Results. Two of 35 patients (6%) developed NPPB immediately after AVM resection. Results of TCD studies were consistent with vasomotor paralysis. NPPB and vasomotor paralysis abated together in both patients on postoperative day 3 to 4. In one patient, NPPB and vasomotor paralysis reoccurred on postoperative day 8 after liberalization of blood pressure control.

CONCLUSIONS

NPPB occurs in a small fraction of patients after AVM resection. The occurrence of NPPB correlates with vasomotor paralysis, and both are present immediately postoperatively and last several days. Improving vasomotor tone and clinical condition do not imply complete normalization of the cerebral circulation because NPPB and vasomotor paralysis can reoccur after liberalization of blood pressure control.

Territorial and microvascular perfusion impairment in brain arteriovenous malformations

BACKGROUND AND PURPOSE

Both the existence and clinical relevance of a steal phenomenon in brain arteriovenous malformations (AVMs) remains a matter of debate. This study aimed to assess perfusion in the brain adjacent to brain AVMs and to relate these to macrovascular blood flow in a single measurement.

MATERIALS AND METHODS

Twenty consecutive patients with AVMs with a median age of 37 years were evaluated by 3T MR imaging by using 3D time-resolved MR angiography to determine blood flow and perfusion patterns. Cerebral perfusion was estimated by using an arterial spin-labeling technique in vascular territories around the nidus and in symmetric regions of interest in the ipsilateral and contralateral hemispheres. Mapping of concentric shells around the nidus was used to define the immediate and adjacent brain and relative perfusion reductions >20% of baseline, termed perinidal dip (PND).

RESULTS

A significant reduction in perfusion ratios between ipsilateral and contralateral hemispheres remote to the AVMs was demonstrated in the middle and posterior cerebral artery territories. PND was detected in 5 patients, and 17 patients overall showed reduced perfusion in the perinidal region on visual inspection. There was a negative correlation of the hemispheric territorial perfusion with the affected/nonaffected inflow time ratio (R = -0.402, P = .015).

CONCLUSIONS

The perfusion impairment in vascular territories adjacent to brain AVMs that we identified as PND may reflect the existence of 2 levels of perfusion impairment: a territorial and a microvascular perfusion disturbance. Although the hemispheric asymmetry in territorial perfusion seems the result of arterioarterial redistribution, the PND was inhomogeneously distributed within a single vascular territory and thus might result from low perfusion pressure in small arteries and arterioles.

Neuropsychological effects of brain arteriovenous malformations

Brain arteriovenous malformations (AVM's) are developmental, chronic lesions that provide unique information about the human brain and can be a useful model for neuroscientists to study cerebral reorganization and hemodynamics. We review the neuroanatomy, epidemiology, natural history, imaging and treatment of brain AVMs, and provide a model with which to better understand neuropsychological functioning and brain reorganization. We suggest that future studies must exclude ruptured AVMs if they wish to further explain focal neurological/cognitive deficits associated with this neurovascular anomaly.

Multimodal ultrasound assessment of cerebral hemodynamics in a patient with a diffuse cerebral angiomatosis

Recent newly developed ultrasound (US) techniques extend our ability to study the cerebral hemodynamics in patients with arteriovenous malformations (AVM) beyond the conventional cerebral blood flow velocity (CBFV) analysis. We present US data of global cerebral blood flow (CBF) and global cerebral circulation time (CCT) in a patient with a unique bihemispherial diffuse cerebral angiomatosis and compare them with 10 age-matched controls. In addition, the estimation of an US-derived global cerebral blood volume (CBV) is proposed. Duplex sonographic CBF analysis revealed 2620 mL/min in the patient and 754 +/- 93 mL/min in controls. Doppler sonographic CCT was 2.9 s and 6.3 +/- 1.5 s and CBV 126 mL and 79 +/- 19 mL, respectively. US allows a simple, minimal invasive bedside analysis of several global hemodynamic parameters that might provide valuable additional information in patients with diffusely altered cerebral hemodynamics.

Cerebral hemodynamics and metabolism in patients with cerebral arteriovenous malformations: an evaluation using positron emission tomography scanning

OBJECT

The purpose of this study was to evaluate cerebral hemodynamic and metabolic features in patients with arteriovenous malformations (AVMs) by using positron emission tomography (PET) scanning.

METHODS

Twenty-four patients with supratentorial cerebral AVMs participated in PET studies in which 15O inhalation steady-state methods were used. The authors recorded the values of regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), the regional oxygen extraction fraction (rOEF), and the regional cerebral metabolic rate of O2 (rCMRO2) at three designated regions of interest (ROIs) in each patient. These ROIs included perilesional (ROI-p), ipsilateral remote (ROI-i), and contralateral symmetrical (ROI-c) brain regions. To identify the factors that exert a direct effect on the hemodynamics of brains affected by AVM, we also separated the lesions according to their size and flow type shown on angiograms, and grouped the patients according to the presence or absence of progressive neurological deficits. We then compared the PET parameters at different ROIs in individual patients and evaluated the mean values obtained for all 24 patients according to AVM flow type and size, and the presence or absence of progressive neurological deficits.

CONCLUSIONS

Overall, mean rCBV and rOEF values were significantly higher in ROI-p than in ROI-c (p = 0.00046 and p = 0.015, respectively). No significant differences were seen between the ROI-i and ROI-c with respect to rCBF, rCBV, and rOEF. Mean rCMRO2 values were similar in the three ROIs; however, the mean rCBF was significantly lower in the ROI-p than in the ROI-c in patients with high-flow AVMs (p = 0.019), large AVMs (p = 0.017), and progressive neurological deficits (p = 0.021). Furthermore, the mean rOEF values were significantly higher in the ROI-p than in the ROI-c in patients with high-flow AVMs (p = 0.005), large AVMs (p = 0.019), and progressive neurological deficits (p = 0.017). The PET studies revealed hemodynamic impairment characterized by decreased rCBF and increased rOEF and rCBV values in the ROI-p of patients with large, high-flow AVMs regardless of whether they exhibited progressive neurological deficits.

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.

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.

Differences in radiosensitivity between brain, small and large arteriovenous malformations. A tentative explanation of the incongruent results of radiotherapy

Intriguing differences in the results of brain arteriovenous malformation (AVM) therapy with ionizing radiation are reported in the literature, i.e. AVMs obliterate at different time intervals from the initiation of radiotherapy although presenting with similar nidus volumes that are treated with the same radiation dose. The purpose of this paper is to present a new concept that explains the variety of results after radiotherapy. To account for an individual AVM's responsiveness to radiotherapy, four variables have been identified from the literature. The variables are factors that are generally accepted to influence the biological effect of radiation. Combined, they can visualize a variety of AVM tissues as well as surrounding normal brain. These hypothesized variations in the type of tissues are then matched with the incongruent results of radiotherapy in order to clarify the issue. Future clinical research programs and possible therapeutical implications of this concept are proposed and discussed.

Brain energy metabolism in early blind subjects: neural activity in the visual cortex

As an attempt to better understand the metabolic basis for the previously reported increases in glucose metabolism in the visual cortex of congenitally blind subjects, cerebral blood flow, oxygen consumption and glucose utilization were investigated with multitracer positron emission tomography. Measurements were carried out in three subjects who became blind early in life and in three age-matched blindfolded controls. Regional analysis of cerebral blood flow, metabolic rates for oxygen and glucose utilization revealed that these parameters were relatively higher in the visual cortex in case of early blindness (109.7 +/- 2.4%; 114.3 +/- 1.5%; 118.0 +/- 5.5%, respectively) than in controls (98.1 +/- 3.9%; 108.6 +/- 3.6%; 105.2 +/- 4.8%). There were slight differences, albeit statistically not significant, between early blind and control subjects in terms of oxygen-to-glucose metabolic ratios. The relatively preserved stoichiometry in the visual areas of blind subjects points to the lack of variation in the yield of glucose oxidation in this cortex. Those observations suggest that the high level of energy metabolism disclosed in early blind visual cortex is related to neural activity.

Brain tissue gases and pH during arteriovenous malformation resection

OBJECTIVE

The purpose of this study was to determine whether baseline partial pressure of oxygen (PO2), partial carbon dioxide pressure (PCO2), and pH in brain tissue adjacent to arteriovenous malformations (AVMs) are different from those in control patients. In addition, PO2, PCO2, and pH changes were measured during resection of the AVMs.

METHODS

Two groups were studied. Group 1 (n = 8) was composed of nonischemic patients scheduled for cerebral aneurysm clipping. Group 2 (n = 13) was composed of patients undergoing neurosurgery for resection of AVMs. After the craniotomy, the dura was retracted and a combined PO2, PCO2, and pH sensor was inserted into nonischemic brain tissue in Group 1. In Group 2, the sensor was inserted into tissue 2 to 3 cm from the margin of the AVMs, within the same arterial blood supply. After equilibration of the sensor, tissue gases and pH were measured during steady-state anesthetic conditions in Group 1 and during resection of AVMs in Group 2.

RESULTS

Under baseline conditions before the start of surgery, tissue PO2 was decreased in patients with AVMs compared with control patients, but PCO2 and pH were not changed. During resection of the AVMs, PO2 and pH increased and PCO2 decreased compared with baseline measurements. These parameters did not change in control patients during a similar time period.

CONCLUSION

The results suggest that cerebrovascular or metabolic adaptation occurs in patients with AVMs with decreased tissue perfusion pressure as an adjustment for decreased oxygen delivery. During resection of AVMs, this adaptation produces a relative hyperemic environment with tissue hyperoxia, hypocapnia, and alkalosis that is not corrected by the end of surgery.

Functional imaging of cerebral arteriovenous malformations with a comment on cortical reorganization

Functional brain imaging is poised to become a standard diagnostic tool. The authors review their experience using functional positron emission tomography (fPET) in patients with cerebral arteriovenous malformations (AVMs).

Twelve patients, three males and nine females aged 16 to 30 years, 11 with a cerebral AVM and one with a cavernous angioma, of which five were located in the central area and seven in a speech region, underwent fPET and three-dimensional magnetic resonance imaging. These studies were coregistered in stereotactic space and correlated to Brodmann's areas that were identified from the atlas of Talairach and Tournoux. Vibrotactile and/or motor stimulation of the contralateral hand were used to identify the central region in patients whose AVM resided within, or close to, the motor strip, and language tasks specifically designed to activate visual, auditory, expressive, or semantic language were used in patients whose AVM resided within, or close to, Broca's or Wernicke's areas.

Somatosensory and motor activation reliably identified the central region in all cases as validated by identification of Brodmann's areas and by intraoperative cortical mapping, which was performed with the patient under local anesthesia. Similarly, language tasks accurately lateralized major language function to one hemisphere concordantly with neuropsychological assessment, including dichotic listening and intracarotid Amytal tests, and localized language areas appropriately as verified by stereotactic coordinates.

Functional cerebral imaging is feasible in patients with structural brain lesions. It is a reliable method to identify the relationship of a cerebral AVM to the central region. The determination of a similar relationship to language areas is dependent on the development and further validation of language-based tasks designed to activate visual, auditory, expressive, and semantic aspects of language specific to particular sites within the anterior and posterior speech regions.

Postoperative cognitive and single photon emission computed tomography assessment of patients with resection of perioperative high-risk arteriovenous malformations

We studied the outcome of 10 patients who had undergone high-risk surgery for an arteriovenous malformation at our institution between November 1991 and November 1993. All of the lesions were located in the dominant (left) hemisphere. Perioperative risk was assessed by the location of the lesion in functionally eloquent cortex (seven patients) or deep structures (two patients) or the lesion's large volume (two patients). Our patients included six women and four men, and their ages ranged from 22 to 53 years (mean, 35.8). Our follow-up study included the evaluation of neurological sequelae but mainly emphasized the study of cognitive deficits (seven major functional clusters), the incidence of depression and behavioral changes, and the assessment of regional cerebral blood flow with single photon emission computed tomography. Six patients returned to a seemingly "normal" daily life with some minor deficits postoperatively, three developed contralateral hemiparesis, and one had disabling cognitive deficits. Our comprehensive cognitive assessment, in particular, showed that although patients might appear "normal" on a routine neurological examination, most patients showed a mild deficit in at least one cognitive function and three were severely impaired. In addition, the single photon emission computed tomographic studies pointed out hypoperfusion in more extensive regions than the surgical defects shown by magnetic resonance imaging or computed tomographic studies. These single photon emission computed tomography images helped to explain some of the cognitive and behavioral changes better than the anatomic studies. This information will make it possible for the physician to offer continuing supportive care for the patient in postoperative transition to normal life activities.

Vascular malformations and epilepsy: clinical considerations and basic mechanisms

Vascular malformations (VMs) are associated with epilepsy. The natural history of the various VMs, clinical presentation, and tendency to provoke epilepsy determine treatment strategies. Investigations have probed the mechanisms of epileptogenesis associated with these lesions. Electrophysiologic changes are associated with epileptogenic cortex adjacent to VMs. Putative pathophysiologic mechanisms of epileptogenesis include neuronal cell loss, glial proliferation and abnormal glial physiology, altered neurotransmitter levels, free radical formation, and aberrant second messenger physiology.

Localization of motor areas adjacent to arteriovenous malformations. A positron emission tomographic study

Motor cortex activity was localized with positron emission tomography (PET) in 4 patients with large arteriovenous malformations adjacent to or undercutting the left primary motor cortex. Relative cerebral blood flow responses were measured during execution of a visually guided motor tracking task performed with the right index finger, hand, great toe, tongue, or eyes alone (control) and mapped onto each patient's corresponding magnetic resonance imaging (MRI) scan. The relative cerebral blood flow responses in the contralateral precentral gyrus, adjacent to each arteriovenous malformation, demonstrated a normal somatotopic distribution, similar to that in a control population. In the 3 patients with preserved motor function, responses were also present in the ipsilateral primary motor cortex, bilateral supplementary motor area, and ipsilateral anterior cerebellum, similar in location to those of a control population. In the fourth patient with a hemiparesis, responses were attenuated in the primary motor cortex, increased in the supplementary motor area, and absent in the cerebellum. The results demonstrate that PET cerebral blood flow mapping can localize motor cortex despite the presence of significant blood flow abnormalities in adjacent arteriovenous malformations. The method, particularly when combined with MRI, may be used in the planning of surgical, radiation, or embolization therapy.

Dementia with leucoaraiosis and dural arteriovenous malformation: clinical and PET case study

A case of rapidly progressive dementia with diffuse leucoaraiosis on CT was attributable to a supratentorial dural arteriovenous malformation. Positron emission tomography (PET) showed low cerebral blood flow and high oxygen extraction ratio throughout the cerebral hemispheres indicating a state of chronic haemodynamic compromise which could predispose to the development of a vascular dementia. CT images of dilated intracerebral veins suggested that a venous drainage overload rather than a vascular steal phenomenon might be involved in the pathophysiology of the dementia of vascular origin.

Pressure autoregulation is intact after arteriovenous malformation resection

The loss of autoregulatory control of cerebral perfusion to changes in perfusion pressure in tissue remote from an arteriovenous malformation (AVM) has been proposed as the mechanism underlying "normal perfusion pressure breakthrough." This study is the first direct test of this mechanism. Studies were performed during the resection of moderate to large AVMs in 25 patients undergoing 28 procedures under isoflurane anesthesia. Cerebral blood flow (CBF) was measured (xenon-133 method) in the hemisphere adjacent to the nidus before resection after dural exposure (pre), after AVM removal before dural closure at spontaneous systemic blood pressure (post), and, finally, with the mean arterial pressure increased by 20 mm Hg, using phenylephrine (post-BP). AVM resection resulted in a significant enhancement of perfusion in the adjacent hemisphere (30 +/- 2 vs. 25 +/- 1 ml/100g/min, P < 0.01), but no further increase of CBF occurred during increased perfusion pressure (30 +/- 2 ml/100g/min). One patient suffered a postoperative hemorrhage and another developed intraoperative brain swelling during the course of the resection that necessitated staging the procedure. These two patients had the highest increases in CBF, but intact pressure autoregulation. Preserved autoregulation to increased mean arterial pressure after resection does not support a hemodynamic mechanism for the observed increase in CBF from before the resection to after the resection. Pathological events, however, do appear to be related to increases in hemispheric perfusion.

The treatment of associated intracranial aneurysms and arteriovenous malformations

Cerebral arterial aneurysm associated with arteriovenous malformation (AVM) has been described with a variable incidence, averaging 10% of AVM cases. The present series includes 39 patients with this association, derived from a total of 400 patients with AVM's evaluated and treated since 1970. The aneurysms are classified into four major groups, each carrying particular therapeutic implications. Optimum treatment of these lesions is based in part on a knowledge of the hemodynamic alterations associated with the AVM's. In most of these cases, the symptomatic lesion was treated first; occasionally, when feasible, both lesions were treated during the same operation. All patients had some form of treatment, either surgical or endovascular, directed to at least one of the two types of lesions. All symptomatic lesions were treated and all ruptured aneurysms were obliterated. There were no deaths in this series.

Positron emission tomography in cerebrovascular disorders

The introduction of positron emission tomography (PET) as a powerful imaging modality has played a major role in the understanding of the pathophysiological bases for cerebrovascular disorders. PET is the only technique that allows measurement of regional cerebral blood flow, blood volume, oxygen extraction fraction, and oxygen and glucose metabolism with detail and accuracy. Using PET, these physiological parameters can be measured to determine the extent of the disease from the early stages of cerebrovascular disorders to acute cerebral infarction. Significant hemodynamic and metabolic abnormalities are noted in chronic ischemia, but no structural changes are noted on anatomic images. PET studies have shown that in many patients in the early phases (10 to 12 hours) of clinically diagnosed acute stroke, a substantial area of ischemia exists, which, if untreated, will become irreversibly damaged. Similar to the results achieved in patients with acute myocardial infarction, appropriate intervention in patients with cerebrovascular disorders may significantly reduce the extent of injury to the brain. PET also has been useful in predicting functional recovery and monitoring the effects of various therapeutic approaches. Although functional imaging of the brain with single photon emission computed tomography can successfully be used in the investigation of several disorders of the brain, its role in cerebrovascular disorders is quite limited. PET is a unique modality that studies ischemic diseases of the brain, and it potentially could play a significant role in the management of patients with cerebrovascular disease. This will be further realized when aggressive approaches are used routinely in the future.