International Subarachnoid Aneurysm Trial II (ISAT II)

  • End date
    Jun 30, 2024
  • participants needed
  • sponsor
    Centre hospitalier de l'Université de Montréal (CHUM)
Updated on 30 July 2023


The purpose of this study is to compare the clinical outcome of surgical clipping and endovascular coiling for ruptured intracranial aneurysms not included in the original ISAT Study.


The International Subarachnoid Aneurysm Trial (ISAT) was a turning point in modern neurosurgical history (1). The trial showed that for 2143 subarachnoid hemorrhage (SAH)patients eligible for both surgery and endovascular coiling, randomized allocation to coiling was associated with better one year clinical outcomes, defined as survival without dependency (absolute risk reduction (ARR) of 7.4% (95%CI; 3.6 - 11.2, p=0.0001). Because ISAT was a positive pragmatic trial, the interpretation of the trial results was that coiling should be adopted as the first-line treatment for ruptured lesions, for patients with the types of aneurysms included in ISAT, of which the great majority were small (≥10 mm) anterior circulation aneurysms.

Although ISAT was well-designed, conducted, and reported, trial results were not always properly interpreted, and endovascular coiling was perhaps inappropriately extrapolated beyond what ISAT demonstrated. Endovascular treatment for ruptured aneurysms has now become first-line treatment in many centers (2), which may be appropriate for small, anterior circulation lesions, but there is no evidence to support this practice for the wide spectrum of non-ISAT patients and aneurysms. A recent pre-randomized study of coiling as first-intention (3)showed better results for those ruptured aneurysms felt to be readily coilable; however, the optimal management of more difficult-to-coil ruptured aneurysms remains unclear.

Further compounding the problem are the concerns that aneurysm coiling may not be as durable in the long-term as surgical clipping, leading many neurosurgeons to continue to clip most ruptured aneurysms in spite of ISAT results.

Proponents of endovascular treatment sometimes justify this extrapolation of ISAT results on the basis of improved catheter and coil technology, although this has never been demonstrated. However, the addition of stents and flow-diverters, which were not tested in ISAT, may increase endovascular treatment risks, especially when combined with dual anti-platelet agents. The introduction of these devices allowed for the expansion of indications of EVT to include wide-necked aneurysms, lesions which would not have been included in ISAT. The wider spectrum of patients and aneurysms now considered for EVT may not all experience the same degree of benefit as seen in the original ISAT trial (4). Considering the relatively small ARR of 7.4% favouring coiling, when the additional risks due to stents are included, the balance may have tipped to favour surgical clipping.

These new questions deserve formal study in the context of a randomized clinical trial.

Condition Intracranial Hemorrhage Ruptured Aneurysm
Treatment surgical management, Endovascular management
Clinical Study IdentifierNCT01668563
SponsorCentre hospitalier de l'Université de Montréal (CHUM)
Last Modified on30 July 2023


Yes No Not Sure

Inclusion Criteria

Patients at least 18 years of age
At least one documented, intradural, intracranial aneurysm, ruptured within last 30 days
SAH WFNS grade 4 or less
The patient and aneurysm are considered appropriate for either surgical or endovascular treatment by the treating team

Exclusion Criteria

Patients with absolute contraindications administration of contrast material (any type)
Patients with AVM-associated aneurysms
Aneurysm located at basilar apex
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