† These authors contributed equally.
Subarachnoid hemorrhage (SAH) has a high mortality rate, and cerebral aneurysm ruptures account for 80% of all cases. Although several previous case studies have reported a headache before aneurysmal SAH, no previous study has reported a case of SAH after a change in the existing migraine pattern without any other clinical signs. A 43-year-old male patient who had suffered chronic migraines for 10 years visited the emergency department due to migraine symptoms, which exacerbated 3 days before the visit. He was admitted for symptom management, and his condition improved after taking migraine-specific medication. However, his consciousness deteriorated, and he became drowsy 8 days from the onset of headache aggravation. Brain computed tomography angiography revealed SAH. A small ruptured aneurysm, which was not detected by brain magnetic resonance angiography performed a few days earlier, was found in the A1 segment of the right anterior cerebral artery. We performed emergency endovascular coil embolization in the right A1 without any other complications. After the procedure, his neurological symptoms no longer exacerbated during hospitalization. He showed only a mild headache after 2 weeks and was discharged. Aneurysmal SAH is one of the most devastating neurological diseases, but early detection and treatment of aneurysms before major rupture may facilitate a good prognosis. If the pattern of previously diagnosed chronic migraine changes suddenly, a minor leak before the major rupture of a cerebral aneurysm should be considered, even if a sentinel headache has not been suggested.