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Jason M. Davies and Michael T. Lawton

settings. Hospital and surgeon case volume have been shown to impact outcomes across a variety of subspecialties, including neurosurgery, 1 , 2 , 4 , 5 , 13 cardiothoracic surgery, 9 , 11 gastrointestinal surgery, 3 , 7 , 12 and breast surgery. 8 At present, there are no published reports of volume-outcome relationships for cerebrovascular malformations. Demonstration of these relationships is important in the current sociopolitical landscape, wherein legislation seeks to optimize cost and quality. Determining and examining the factors that contribute to differences

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Oliver Y. Tang, James S. Yoon, Anna R. Kimata and Michael T. Lawton

guided the development of emergency transport patterns. 10 , 14 , 35 Research on the volume-outcome relationship (VOR), the relationship between hospital volume and outcomes, for neurotrauma care may also help to inform these policies. Several studies have demonstrated evidence of improved outcomes at high-volume hospitals across neurosurgical subspecialties, including tumor, vascular, and functional. 4 , 12 , 15 , 34 Despite a more limited evidence base for pediatric neurosurgery, partly because of the lower overall volume, 25 positive VORs have also been observed

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Zachary A. Seymour, Penny K. Sneed, Nalin Gupta, Michael T. Lawton, Annette M. Molinaro, William Young, Christopher F. Dowd, Van V. Halbach, Randall T. Higashida and Michael W. McDermott

for AVMs to surgical series is not straightforward, as total AVM volume rather than SM grade is the most important factor for SRS risk stratification. 5 Select small AVMs (< 10 ml) have a 3-year obliteration rate of 70%–95%. 18 , 27 , 28 Single-session SRS for the treatment of SM Grade I–II AVMs using a median radiation dose of 22 Gy can have an obliteration rate as high as 90% at 5 years. 16 Radiation dose and treatment volume play important roles in the rates of AVM obliteration; Pan et al. reported only a 25% overall obliteration rate at 40 months for single

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Michael T. Lawton and Michael J. Lang

including the Carotid Occlusion Surgery Study in 2011, A Randomized Trial of Unruptured Brain Arteriovenous Malformations (ARUBA) in 2014, and multiple clinical trials validating the efficacy of mechanical thrombectomy for acute ischemic stroke caused by large vessel occlusion in 2015. 14 , 40 , 49 These events eroded the microsurgical case volume and threatened the future of open vascular neurosurgery, shifting market forces and patient attitudes toward alternative endovascular and radiosurgical therapies. These three decades transformed vascular neurosurgery into a

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Robert M. Starke, Felipe C. Albuquerque and Michael T. Lawton

It is with great pleasure that we present this Neurosurgical Focus video supplement on supratentorial cerebral arteriovenous malformations (AVMs). We were privileged to view a remarkable number of outstanding videos demonstrating current state-of-the-art management of brain AVMs using endovascular and microsurgical modalities. Careful and critical review was required to narrow down the submitted videos to a workable volume for this supplement, which reflects the excellent work being done at multiple centers with these lesions.

This issue consists of videos that represent modern microsurgical and neuroendovascular techniques for the treatment of supratentorial cerebral AVMs. The videos demonstrate cutting-edge therapies as well as standard ones, which will be valuable to both novice and expert neurointerventionists and neurosurgeons. We are honored to be involved with this project and proud of its content and expert authors. We believe you will enjoy the video content of this supplement and hope that it will raise the collective expertise of our community of AVM surgeons.

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Adib A. Abla, William Caleb Rutledge, Zachary A. Seymour, Diana Guo, Helen Kim, Nalin Gupta, Penny K. Sneed, Igor J. Barani, David Larson, Michael W. McDermott and Michael T. Lawton

(approximately 3 cm in diameter) require reductions in the marginal dose below 16 Gy to avoid adverse radiation complications, 19 while 16-, 18-, and 20-Gy marginal doses are associated with 70%, 80%, and 90% obliteration rates for AVMs overall. 22 Volume-staged SRS (VS-SRS) is a newer strategy that divides a large AVM into 2 or 3 smaller portions that are treated at separate stages enabling each portion to receive a higher dose. 12 , 22 The higher dose may be associated with a greater likelihood of response, while the separation of stages by months and proper alignment of

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Zaman Mirzadeh, Nader Sanai and Michael T. Lawton

mass, relatively small luminal volume of the ACoA aneurysm, and filling of the left pericallosal and callosomarginal arteries. B: Lateral view in the late arterial phase (left ICA injection) showing the separate origins of the PcaA and CmaA at the aneurysm base. C: An AP view (right ICA injection) demonstrating that the aneurysm did not fill from the right A 1 segment. The aneurysm was deemed unclippable. The azygos ACA bypass was performed, revascularizing the distal left PcaA and CmaA with the bypass, and the aneurysm was trapped ( Fig. 3 ). Postoperative

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Fred G. Barker II

transplantation as practical realities for the entire community. Similar examples within neurosurgery will occur to every reader. Two of the iron laws of surgery—the learning curve and the volume outcome effect—predict that by placing an artificial ceiling on the operative experience of leading surgeons, we risk delaying the progress of operative neurosurgery in the broadest sense. Zygourakis and colleagues documented equivalent outcomes after surgery for overlap, even against the optimistic comparator of an equally skilled surgeon operating without overlap during prime

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Arnau Benet, Jordina Rincon-Torroella, Michael T. Lawton and J. J. González Sánchez

Evaluation of Carcinogenic Risks to Humans. Volume 71: Re-Evaluation of Some Organic Chemicals, Hydrazine and Hydrogen Peroxide Lyon , IARC Press , 1999 . 749 – 767 22 World Health Organization : IARC Monographs on the Evaluation of Carcinogenic Risks to Humans Volume 88: Formaldehyde, 2-Butoxyethanol and 1- tert -Butoxypropanol-2-ol Lyon , IARC Press , 2006

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Michael T. Lawton, Ronald Jacobowitz and Robert F. Spetzler

53. Rekate HL : Circuit diagram of the circulation of cerebrospinal fluid. Pediatr Neurosurg 21 : 248 – 253 , 1994 Rekate HL: Circuit diagram of the circulation of cerebrospinal fluid. Pediatr Neurosurg 21: 248–253, 1994 54. Rekate HL , Brodkey JA , Chizeck HJ , et al : Ventricular volume regulation: a mathematical model and computer simulation. Pediatr Neurosci 14 : 77 – 84 , 1988 Rekate HL, Brodkey JA, Chizeck HJ, et al: Ventricular volume regulation: a mathematical model and