When arteriovenous malformations (AVMs) of the brain were first described in the middle of the 19th century, deciding on treatment was easy, because there was none. Since the first reports of the neurosurgical exposure of brain AVMs at the end of that century,^1,2 their management has been dogged by controversy. In 1928, Cushing and Bailey wrote, “…to extirpate one of these aneurysmal angiomas in its active state would be unthinkable…”,³ but, while their book was in press, Walter Dandy published a case series of people whose brain AVMs had been surgically resected (with variable success).⁴ Later developments in catheter angiography, bipolar coagulation, the operating microscope, and stereotactic surgery have all encouraged surgical intervention and no doubt improved the completeness and safety of resection.^5,6 However, clinicians still struggle with the original dilemma of whether some brain AVMs should be treated at all.

Interventions for brain AVMs diversified during the latter half of the 20th century, giving clinicians a further dilemma about which intervention to use should treatment be appropriate. Endovascular embolisation, by injecting artificial agents in the afferent feeding vessels of brain AVMs, was first reported in 1960.⁷ The technique has been refined ever since, initially as an adjunct to neurosurgical excision,⁸ but more recently, with the development of microcatheters and liquid polymer glues, as a potentially curative procedure.⁹ Unfractionated stereotactic radiotherapy, confusingly referred to as "radiosurgery" by some, was first used to treat brain AVMs a decade after the first report of endovascular embolisation.¹⁰ Stereotactic radiotherapy, using gamma knife, linear accelerator, and charged particle (proton beam) techniques, can provoke vascular obliteration of compact brain AVMs ⩽3 cm in diameter and of larger AVMs that have been reduced to this size with embolisation. Despite the chronology of the development of these …