Spontaneous bleeding of an arachnoid cyst: a rare cause of thunderclap headache

Introduction A thunderclap headache is a severe that starts suddenly and may be sign of condition can life threatening. Objective To present case rare cause headache. Case presentation 37-year-old female patient was admitted in the neurological emergence service private hospital city São Paulo. She had sudden, explosive, pulsatile headache, with photophobia phonophobia. The examination no focal signs. deep vein thrombosis 2014 past since then she has been irregularly using Warfarin. underwent CT MRI skull showed enlargement bilateral retrovermian retrocerebellar cerebrospinal fluid space, thin membranes/septations inside, heterogeneous content, deposition hemoglobin degradation products. Such findings are consistent arachnoid cyst hemorrhagic content. INR 1. Conservative symptomatic treatment started, control performed on second day hospitalization, demonstrating almost complete reabsorption hematic material. discharged after 2 days hospitalization improvement. Conclusion Arachnoid cysts collections located between meningeal membranes. They congenital formed due to valve defect membranes leading collection (CSF) its interior. Most an incidental finding. About 1 2% population symptoms appear when increases size or bleeds. Our complication not related use anticoagulant. Keywords: Thunderclap Cyst Bleeding, Cyst.