Treatment of Brain AVMs (TOBAS) Study: A Randomized Controlled Trial and Registry

Intracranial arteriovenous malformations (AVMs) are relatively uncommon but increasingly discovered lesions that can lead to significant neurological disability or death.1 Population-based data suggest that the annual incidence of discovery of a symptomatic AVM is approximately 1.1 per 100 000 population.7. AVMs commonly present following an intracranial hemorrhage or seizure, although with contemporary brain imaging techniques, an increasing number of incidental lesions are found.2

Intracranial AVMs are typically diagnosed before the age of 40 years old, with more than 50% of patients presenting following an intracranial hemorrhage, the most feared sequelae of harbouring an AVM.3 An AVM-related seizure is reported as the presenting feature in 20-25% of cases4, 5 and although these can sometimes be successfully managed with anti-epileptic agents, some AVMs lead to intractable seizures in spite of medication. Other presentations include headaches, focal neurological deficits, or pulsatile tinnitus.1

The available natural history studies indicate an overall risk of initial hemorrhage of approximately 2% to 4% per year, although the long-term consequences in terms of the probability of death or long-term disability following intracranial hemorrhage remains unclear.6-8 Mortality from the first hemorrhage has been reported to occur between 10-30% of patients with a ruptured AVM, although some more recent data suggest that the mortality rate may be lower and only 10-20% of survivors have long-term disability.9-11 Hemorrhagic presentation is considered the most reliable risk factor for a repeat hemorrhage.6, 8 Unfortunately, the natural history data available is not of sufficient quality (Level V) to support making management recommendations.

Over the last decade, there have been substantial developments in the management of intracranial AVMs. There has been an evolution of microsurgical as well as endovascular and radiosurgical techniques to treat these lesions. As the management options have evolved, individual and combined modality treatment protocols have been developed in different institutions for the management of AVMs. Current interventional therapy for brain arteriovenous malformations (BAVMs) is varied and includes open neurosurgical resection, radiosurgery, and endovascular management, either alone or in combination. The choice of management is largely dependent on the decisions of the local physicians that make up the treatment team, and a recent survey has demonstrated substantial variability in decision-making for almost all AVMs.12

Interventional therapies, when they are performed, are assumed to decrease the risk of initial or subsequent hemorrhage and therefore lead to better long-term outcomes, an assumption that has yet to be proven.