International Subarachnoid Aneurysm Trial

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The International Subarachnoid Aneurysm Trial (ISAT) was a large multicentre, prospective randomised clinical medical trial, comparing the safety and efficacy of endovascular coil treatment and surgical clipping for the treatment of brain aneurysms. The study began in 1994. The first results were published in The Lancet in 2002, and the 10 year data were published again in The Lancet in early September 2005. 2,143 study participants were mostly drawn from U.K. hospitals with the rest drawn from North American and European hospitals.

The study found better results with endovascular coil treatment compared to surgical clipping, however subsequent studies have questioned this conclusion.[1] The study was criticised by many clinicians and not well accepted by surgeons.[2]:206-07 Primary criticisms were related to the study's patient population's generalisability to the wider population, and the long term prognosis of coil embolisation.[3]

Study design and results[edit]

ISAT sought to measure outcomes of cerebral aneurysm patients at 2 and 12 months using a type of a Rankin scale.[4]:114 The study was halted in 2002 after the oversight committee found increased morbidity with clipping over endovascular coiling.[4]:114


ISAT was criticised on a number of factors, many related to the randomization of the patient population. The patient population was on average younger, and the majority had aneurysms under 10 mm and in anterior circulation.[1] The randomized patient population in the ISAT was younger on average than the population of subarachnoid hemorrhage patients in the U.S. and Japan.[5]:210 In response to these criticisms a facility that participated in ISAT compared the clinical outcomes of their patients that were not selected for the study to those that were. They reported finding outcomes similar to the ISAT.[1]

Subsequent analysis[edit]

Although the initial ISAT analysis appeared to favor endovascular coiling over microsurgical clipping, subsequent meta-analysis have questioned that conclusion, finding higher incidences of recurrence.[6] A large meta-analysis from Johns Hopkins University published in Neurosurgery concluded that "there is no clear consensus in these two studies or in the 45 observational studies included."[6]

Updated data from the ISAT group in March 2008 shows that the higher aneurysm rate of recurrence is also associated with a higher rebleeding rate, given that the rebleed rate of coiled aneurysms appears to be 8 times higher than that of clipping treated aneurysms in this study.[7] The ISAT authors conclude that "when treating ruptured cerebral aneurysms, the advantage of coil embolization over clip ligation cannot be assumed for patients < 40 years old."[7] Other subsequent studies have questioned the ISAT's conclusions directly.[8] This conclusion is based on a number of methodological assumptions itself and other authors have cautioned about extending it to other patient populations.[9]

It appears that although endovascular coiling is associated with a shorter recovery period as compared to surgical clipping, it is also associated with a significantly higher recurrence rate after treatment. The long-term data for unruptured aneurysms are still being gathered.

See also[edit]


  1. ^ a b c AJNR Am J Neuroradiol. 2005 Feb;26(2):367-72.
  2. ^ Michael Forsting, Isabel Wanke, Intracranial Vascular Malformations and Aneurysms: From Diagnostic Work-Up to Endovascular Therapy, Springer 2008, ISBN 3-540-32919-6.
  3. ^ Michael J. Alexander, Robert Friedrich Spetzler, Pediatric neurovascular disease: surgical, endovascular, and medical management, Thieme: 2006, ISBN 1-58890-368-0, page 145.
  4. ^ a b Michael S. Horowitz, Elad I. Levy, Neuroendovascular surgery, Karger Publishers, 2005, ISBN 3-8055-7781-8.
  5. ^ Adnan I. Qureshi, Textbook of Interventional Neurology, Ed. Adnan I. Qureshi, Alexandros L. Georgiadis, Cambridge University Press: 2011, ISBN 0-521-87639-7.
  6. ^ a b See, Raja PV, Huang J, Germanwala AV, Gailloud P, Murphy KP, Tamargo RJ. Microsurgical clipping and endovascular coiling of intracranial aneurysms: A critical review of the literature. Neurosurgery 62: 1187-1202, June 2008
  7. ^ a b Mitchell P, Kerr R, Mendelow AD, Molyneux A. Could late rebleeding overturn the superiority of cranial aneurysm coil embolization over clip ligation seen in ISAT? Journal of Neurosurgery 108: 437-442, March 2008
  8. ^ See, J Neurosurg. 2010 Oct;113(4):795-801.
  9. ^ J Mocco, L. Nelson Hopkins, "International Subarachnoid Aneurysm Trial analysis", Journal of Neurosurgery, March 2008 / Vol. 108 / No. 3 / Pages 436-436.

External links[edit]