may be detected incidentally on brain imaging; this presents a conundrum, as all treatments for cerebral aneurysms are associated with potential complications. The International Study of Unruptured Intracranial Aneurysms (ISUIA) provided prognostic data both in people having previously had a subarachnoid hemorrhage and people who had aneurysms detected by other means. Those having previously had a SAH were more likely to bleed from other aneurysms. In contrast, those having never bled and had small aneurysms (smaller than 10 mm) were very unlikely to have a SAH and were likely to sustain harm from attempts to repair these aneurysms. On the basis of the ISUIA and other studies, it is now recommended that people are considered for preventive treatment only if they have a reasonable life expectancy and have aneurysms that are highly likely to rupture. Moreover, there is only limited evidence that endovascular treatment of unruptured aneurysms is actually beneficial. Treatment Management involves general measures to stabilize the person while also using specific investigations and treatments. These include the prevention of rebleeding by obliterating the bleeding source, prevention of a phenomenon known as vasospasm, and prevention and treatment of complications. Stabilizing the person is the first priority. Those with a depressed level of consciousness may need to be intubated and mechanically ventilated. Blood pressure, pulse, respiratory rate, and Glasgow Coma Scale are monitored frequently. Once the diagnosis is confirmed, admission to an intensive care unit may be preferable, especially since 15 percent may have further bleeding soon after admission. Nutrition is an early priority, mouth or nasogastric tube feeding being preferable over parenteral routes. In general, pain control is restricted to less-sedating agents such as codeine, as sedation may impact on the mental status and thus interfere with the ability to monitor the level of consciousness. Deep vein thrombosis is prevented with compression stockings, intermittent pneumatic compression of the calves, or both. A bladder catheter is usually inserted to monitor fluid balance. Benzodiazepines may be administered to help relieve distress. Antiemetic drugs should be given to awake persons. People with poor clinical grade on admission, acute neurologic deterioration, or progressive enlargement of ventricles on CT scan are, in general, indications for the placement of an external ventricular drain by a neurosurgeon. The external ventricular drain may be inserted at the bedside or in the operating room. In either case, strict aseptic technique must be maintained during insertion. In people with