OBJECT Subarachnoid hemorrhage (SAH) is usually caused by a ruptured intracranial aneurysm, but in some patients no source of hemorrhage can be detected. More recent data showed increasing numbers of cases of spontaneous nonaneurysmal SAH (NASAH). The aim of this study was to analyze factors, especially the use of antithrombotic medications such as systemic anticoagulation or antiplatelet agents (aCPs), influencing the increasing numbers of cases of NASAH and the clinical outcome. METHODS Between 1999 and 2013, 214 patients who were admitted to the authors' institution suffered from NASAH, 14% of all patients with SAH. Outcome was assessed according to the modified Rankin Scale (mRS) at 6 months. Risk factors were identified based on the outcome. RESULTS The number of patients with NASAH increased significantly in the last 15 years of the study period. There was a statistically significant increase in the rate of nonperimesencephalic (NPM)-SAH occurrence and aCP use, while the proportion of elderly patients remained stable. Favorable outcome (mRS 0-2) was achieved in 85% of cases, but patients treated with aCPs had a significantly higher risk for an unfavorable outcome. Further analysis showed that elderly patients, and especially the subgroup with a Fisher Grade 3 bleeding pattern, had a high risk for an unfavorable outcome, whereas the subgroup of NPM-SAH without a Fisher Grade 3 bleeding pattern had a favorable outcome, similar to perimesencephalic (PM)-SAH. CONCLUSIONS Over the years, a significant increase in the number of patients with NASAH has been observed. Also, the rate of aCP use has increased significantly. Risk factors for an unfavorable outcome were age > 65 years, Fisher Grade 3 bleeding pattern, and aCP use. Both "PM-SAH" and "NPM-SAH without a Fisher Grade 3 bleeding pattern" had excellent outcomes. Patients with NASAH and a Fisher Grade 3 bleeding pattern had a significantly higher risk for an unfavorable outcome and death. Therefore, for further investigations, NPM-SAH should be stratified into patients with or without a Fisher Grade 3 bleeding pattern. Also, cases of spontaneous SAH should be stratified into NASAH and aneurysmal SAH.
Keywords: CVS = cerebral vasospasm; DCI = delayed cerebral infarction; DSA = digital subtraction angiography; Fisher Grade 3; LDA = low-dose acetylsalicylic acid; NASAH = nonaneurysmal SAH; NPM = nonperimesencephalic; PM = perimesencephalic; SAH = subarachnoid hemorrhage; WFNS = World Federation of Neurosurgical Societies; aCP = systemic anticoagulation or antiplatelet agent; aSAH = aneurysmal subarachnoid hemorrhage; anticoagulation; antiplatelet agent; mRS = modified Rankin Scale; nonaneurysmal subarachnoid hemorrhage; nonperimesencephalic; vascular disorders.