[Natural history for residual intracranial AVM: compared with that for conservatively treated AVM].

It is generally accepted that the most suitable treatment of AVM is surgical removal which does not cause neurological deficits. But in some cases, it is impossible to treat surgically because of size or location, so the patient is unfortunately discharged with some part of the nidus remaining. In this paper, we report the natural history of residual AVMs in which part of the nidus remained after initial therapy, and try to ascertain whether therapeutic reduction of the nidus is more effective in preventing intracranial hemorrhage than conservative treatment. Of 362 cases, residual AVMs were found in 35 cases, and were followed up for 9.2 years on average. Eighty cases treated with only conservative therapy were also followed up for 10.9 years on average. The annual risk of intracranial hemorrhage for residual AVMs was 2.9% and that for conservatively treated AVMs was 3.0%, not a significant difference. There was no difference between the two groups in mortality or ADL. We conclude that therapeutic reduction of the nidus was not effective in preventing intracranial hemorrhage.