The excessive formation of free radicals in subarachnoid hemorrhage occurs through different pathways like extracellular hemoglobin conversions, disruption of mitochondrial respiration, and upregulation of enzymes producing free radicals: inducible nitric oxide synthase, NADPH oxidase (NOX), xanthine oxidase and other [30]. This evidence concerns the gene NOS2 and subarachnoid hemorrhage.