The study was a prospective observational epidemiologic study. A randomized controlled trial was considered, but the assumption was that few neurosurgeons would be willing to randomize patients, and there were anticipated difficulties obtaining consent. Participants included 68 neurosurgical centers in 14 countries (USA, Japan, Italy, and United Kingdom), and 3,521 patients were entered into the database. The patients were stratified by age, sex, hypertension, site, and size of aneurysm. Assessments were performed by neurologists unaware of the timing of surgery. The data forms included demographic data, neurologic assessments on admission (≤ 3 days from first subarachnoid hemorrhage), results from computed tomography and cerebral angiography, neurologic and medical complications, operative conditions, and surgical techniques. The Glasgow Outcome Scale was used to obtain 6-month follow-up assessments.

The article identified several crucial factors associated with poor results. The leading cause of poor outcome was cerebral vasospasm, resulting in death or disability in 14% of patients. Rebleeding was the second most common cause of poor outcome in 8% of patients. Other contributing factors were operative complications, intracerebral hematoma, and hydrocephalus. Other major findings included better outcome in patients who were alert on presentation, younger age predicting better outcome, and good outcome still present in more than one in four patients older than 70 years.

Satisfactory outcome was also related to size of the aneurysm (smaller, < 12 mm) and location (patients with an anterior circulation aneurysm had better outcome than patients with a posterior circulation aneurysm). The study also identified indicators for good outcome and included lower admission blood pressure, thin clot on computed tomography, absent comorbidity, absence of cerebral vasospasm, better motor response, and good orientation on admission. At 6 months, 75% of the patients had a favorable outcome with a good recovery of 58%, but there was a 25% mortality. The authors stated in the second part of the article on surgical results that “the risk of waiting 2 weeks for surgery is accompanied by a 12% risk for rebleeding and 30% risk of focal ischemic deficits” and stated that “early surgery is feasible from a technical perspective and reduces the risk of rebleeding; however, in this study, it did not appear to have a major influence on the incidence of mortality or morbidity from vasospasm.”

The investigators were “somewhat surprised” that clipping of the aneurysm did not appear to be more difficult when done early and that the risk of premature leak or rupture did not depend on timing of surgery. The message of the International Cooperative Study was that 75% of patients in a good condition and clipped within 3 days may have a good recovery at 6 months and a 25% mortality.

The impact of the International Cooperative Study on the care of patients was significant. It is likely it changed practice all over the world, with more neurosurgeons now opting for surgical repair within 3 days of presentation. On the one hand, it showed the problems with aneurysmal clipping before day 10 in older patients presenting with a poor grade and with associated comorbidity. However, contrary to this belief, several reports did later show that early aggressive management of poor-grade patients could still lead to significant improvement in outcome in approximately 40–50% [11].

Management of subarachnoid hemorrhage also changed dramatically with the introduction of endovascular coiling of aneurysms. In 1990, a detachable bare platinum coil device (Guglielmi) was introduced into clinical practice. Since then, endovascular treatment with coils has gained worldwide acceptance as an effective treatment for cerebral aneurysms, and coil variations have been introduced into the market [12]. Coiling has been a particularly important development in good grade-patients with aneurysmal subarachnoid hemorrhage [13,14,15]. Newer endovascular techniques for patients otherwise bound to become disabled after surgical repair may also change the equation. Flow diverters (pipeline endovascular stent) may have a role in treatment of complex giant aneurysms [16]. Every physician in this field understands very well that multiple factors impact outcome. There are insufficient data to prove that aggressive intensive care cerebrospinal fluid diversion, have an impact on outcome [17]. Antifibrinolytic agents have largely disappeared [18, 19].

Nonetheless we can now look back at a dubious decision to postpone surgery, leading to long-term antifibrinolytic agents to prevent rebleeding. While masterful waiting, it had devastating consequences. Multiple cerebral infarcts as a result of long-term antifibrinolytics are seldomly seen anymore.