Asymptomatic Intracranial Arteriovenous Malformations
Asymptomatic Intracranial Arteriovenous Malformations
Object. Asymptomatic intracranial arteriovenous malformations (AVMs) represent a clinically challenging problem because of the complex decision making that must be undertaken prior to beginning any type of treatment. In addition, the relative infrequency of these lesions means that there is relatively little experience reported in the literature. The authors use a decision-analysis technique to model the considerations that go into determining the treatment of these lesions in an effort to quantify the various risks and overall benefits conferred by the following three treatment strategies: observation/natural history, microsurgery, and stereotactic radiosurgery.
Methods. The authors conducted a thorough literature search to elucidate the risks and outcomes associated with each treatment option. These values were used to build and run a comprehensive Markov model to determine a base-case analysis. All of the input variables were also subjected to sensitivity analysis to identify the most influential input variables and the crossover points in which favored strategies changed.
The base-case analysis suggested that microsurgery was the favored treatment option because this hypothetical cohort accumulated 21.53 quality-adjusted life years (QALYs) over the course of the model compared with the 16.97 QALYs and 16.40 QALYs for stereotctic radiosurgery and observation, respectively. Sensitivity analysis demonstrated that overall major neurological morbidity and mortality were the most influential input variables both perioperatively and during the radiosurgical "latent" period (that is, up to 2 years posttreatment). The maximum acceptable perioperative combined major neurological morbidity and mortality rate was 6.8%. The latent period combined major neurological morbidity and mortality would need to be 0.7% to make radiosurgery favorable in this analysis.
Conclusions. Results of this decision analysis model suggest that microsurgery in the hands of experienced cerebrovascular surgeons, who can expect a less than 6.8% combined rate of major neurological morbidity and mortality, offers patients a greater overall quality of life over time.
Asymptomatic intracranial AVMs are heterogeneous lesions that vary in size and location and possess different arterial supplies and venous drainage patterns. They are congenital lesions and therefore represent an entire lifetime of risk to a patient, a risk believed to be relatively constant. The specific risk, is hemorrhage, which can lead to outcomes of death, major neurological deficits, minor neurological deficits, or no problem at all. These possible outcomes appear to occur in predictable rates of patients when hemorrhages occur. Long-term, well-controlled studies in which therapeutic interventions are studied are difficult to design or conduct because these lesions are relatively uncommon and clinical experience with their treatment is limited.
Intervention for AVMs is, at the core, a statistical proposition. The decision is made to intervene because the likelihood of long-term benefit is outweighed by the short-term risks of the procedure. The decision is difficult because various therapeutic interventions are available for patients harboring such lesions, each with its own risk- benefit profile. In this type of difficult decision-making situation, the tool of decision analysis has frequently been used to aid in making appropriate choices. In this decision analysis the idea is to break down the larger decision into its possible outcomes and to assign a mathematical probability to them. The probabilities can be assigned using the known experiences as reported in the literature. Based on this information, a model can be constructed in which the total value of each individual pathway to an overall outcome will be known. Finally, the most favorable pathway can be chosen for a given clinical situation and the accuracy of this choice challenged through sensitivity analysis in which each input factor is varied through its range of possible values.
Decision analysis has been used to approach AVM treatments in the past for exactly these reasons. Historically, the decision analyses that have been completed have been flawed because the complexity of the decision was not considered or because information concerning the risks and benefits of various treatment options was absent. Ultimately, these analyses become outdated as new information becomes available concerning the risks and benefits of each treatment approach. Iansek, et al., published one of the earliest decision analyses on the treatment of AVMs in which the results suggested that observation was favored over excision. In this study the surgery-related mortality was estimated at 10% and major neurological morbidity at 27%. The accuracy of these numbers could not be challenged by comparison with data from the literature at the time. Moreover, an accurate range could not be established for the purposes of sensitivity testing. In a subsequent decision analysis performed by Fisher the author found lower surgery-related morbidity (8.99%) and mortality (5.54%) estimates and, thus, that surgery was the favored strategy over observation. At the times of his studies, the author did not have the benefit of the more detailed information about natural history and the stratification of the surgical treatment-related risk that has been provided by the Spetzler-Martin grading system. Further studies have since been conducted which confirm surgery as the favored strategy, often with the option of radiosurgery embedded in the analysis.
What follows is an attempt to review and update the process of decision analysis for AVMs. Consideration is given to the most recent material available concerning the natural history of these lesions and the risks and benefits associated with their different treatment modalities. The analysis is limited to Spetzler-Martin Grade I to III AVMs because no consensus for treating larger lesions has emerged.
Object. Asymptomatic intracranial arteriovenous malformations (AVMs) represent a clinically challenging problem because of the complex decision making that must be undertaken prior to beginning any type of treatment. In addition, the relative infrequency of these lesions means that there is relatively little experience reported in the literature. The authors use a decision-analysis technique to model the considerations that go into determining the treatment of these lesions in an effort to quantify the various risks and overall benefits conferred by the following three treatment strategies: observation/natural history, microsurgery, and stereotactic radiosurgery.
Methods. The authors conducted a thorough literature search to elucidate the risks and outcomes associated with each treatment option. These values were used to build and run a comprehensive Markov model to determine a base-case analysis. All of the input variables were also subjected to sensitivity analysis to identify the most influential input variables and the crossover points in which favored strategies changed.
The base-case analysis suggested that microsurgery was the favored treatment option because this hypothetical cohort accumulated 21.53 quality-adjusted life years (QALYs) over the course of the model compared with the 16.97 QALYs and 16.40 QALYs for stereotctic radiosurgery and observation, respectively. Sensitivity analysis demonstrated that overall major neurological morbidity and mortality were the most influential input variables both perioperatively and during the radiosurgical "latent" period (that is, up to 2 years posttreatment). The maximum acceptable perioperative combined major neurological morbidity and mortality rate was 6.8%. The latent period combined major neurological morbidity and mortality would need to be 0.7% to make radiosurgery favorable in this analysis.
Conclusions. Results of this decision analysis model suggest that microsurgery in the hands of experienced cerebrovascular surgeons, who can expect a less than 6.8% combined rate of major neurological morbidity and mortality, offers patients a greater overall quality of life over time.
Asymptomatic intracranial AVMs are heterogeneous lesions that vary in size and location and possess different arterial supplies and venous drainage patterns. They are congenital lesions and therefore represent an entire lifetime of risk to a patient, a risk believed to be relatively constant. The specific risk, is hemorrhage, which can lead to outcomes of death, major neurological deficits, minor neurological deficits, or no problem at all. These possible outcomes appear to occur in predictable rates of patients when hemorrhages occur. Long-term, well-controlled studies in which therapeutic interventions are studied are difficult to design or conduct because these lesions are relatively uncommon and clinical experience with their treatment is limited.
Intervention for AVMs is, at the core, a statistical proposition. The decision is made to intervene because the likelihood of long-term benefit is outweighed by the short-term risks of the procedure. The decision is difficult because various therapeutic interventions are available for patients harboring such lesions, each with its own risk- benefit profile. In this type of difficult decision-making situation, the tool of decision analysis has frequently been used to aid in making appropriate choices. In this decision analysis the idea is to break down the larger decision into its possible outcomes and to assign a mathematical probability to them. The probabilities can be assigned using the known experiences as reported in the literature. Based on this information, a model can be constructed in which the total value of each individual pathway to an overall outcome will be known. Finally, the most favorable pathway can be chosen for a given clinical situation and the accuracy of this choice challenged through sensitivity analysis in which each input factor is varied through its range of possible values.
Decision analysis has been used to approach AVM treatments in the past for exactly these reasons. Historically, the decision analyses that have been completed have been flawed because the complexity of the decision was not considered or because information concerning the risks and benefits of various treatment options was absent. Ultimately, these analyses become outdated as new information becomes available concerning the risks and benefits of each treatment approach. Iansek, et al., published one of the earliest decision analyses on the treatment of AVMs in which the results suggested that observation was favored over excision. In this study the surgery-related mortality was estimated at 10% and major neurological morbidity at 27%. The accuracy of these numbers could not be challenged by comparison with data from the literature at the time. Moreover, an accurate range could not be established for the purposes of sensitivity testing. In a subsequent decision analysis performed by Fisher the author found lower surgery-related morbidity (8.99%) and mortality (5.54%) estimates and, thus, that surgery was the favored strategy over observation. At the times of his studies, the author did not have the benefit of the more detailed information about natural history and the stratification of the surgical treatment-related risk that has been provided by the Spetzler-Martin grading system. Further studies have since been conducted which confirm surgery as the favored strategy, often with the option of radiosurgery embedded in the analysis.
What follows is an attempt to review and update the process of decision analysis for AVMs. Consideration is given to the most recent material available concerning the natural history of these lesions and the risks and benefits associated with their different treatment modalities. The analysis is limited to Spetzler-Martin Grade I to III AVMs because no consensus for treating larger lesions has emerged.
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