The International Subarachnoid Aneurysm Trial (ISAT) was a major study comparing clipping and coiling of ruptured intracranial aneurysms. The trial provided answers that were the subject of multiple letters and editorial comments.

We review the most common critiques that were published in major neurosurgical journals, trying to identify what aspects of ISAT could have been improved, and what questions remain to be studied.

Frequent critiques include imprecise selection criteria, lack of requirement for the technical proficiency of surgical participants, lack of angiographic controls of surgically treated patients, and poorly chosen primary endpoints. Other issues that are often raised are the poor recruitment rate which endangered generalization of results, the excessive delays in performing clipping which led to rebleeding episodes, lack of blinding in the assessment of outcomes, and subjective questionnaires. Nonetheless, the design of the study as a pragmatic trial was appropriate, as was the choice of the primary endpoint. The overall trial results could not be verified for all subgroups of interest, and currently many patients who would not have been included in ISAT are treated by coiling, while other patients are treated by clipping despite ISAT results. Hence a new trial, complementary to the original ISAT, may now be indicated.

ISAT was well-designed and conducted, but many questions remain. They should be addressed by a new trial.