A 14-year-old boy (case 12) presented with aggravating headache and nausea. His headache began 5 years ago on the left temple area, with no neurological deficit. He had no other past medical history. His mother and maternal grandfather had history of malignant hyperthermia and ryanodine receptor type 1 (RyR1) gene mutation. Top left : Magnetic resonance imaging showed a thrombosed aneurysm on the distal internal carotid artery (C1 segment). Top right : Cerebral angiography demonstrated an aneurysm of 9.8 mm in diameter at the stenosed communicating segment of the left internal carotid artery. Lower left : He underwent endosaccular coil embolization with stent assistance. Lower right : Follow-up cerebral angiography at 10 months after treatment showed no evidence of recurrence.