Cerebral Venous Sinus Thrombosis Masquerading as High Altitude Cerebral Edema at Extreme Altitude

Introduction: Extreme altitude travel has gained popularity globally for adventurous, scientific, and military endeavors. Cerebral venous sinus thrombosis (CVST) at extreme altitude is a rare, covert, and emergent condition requiring immediate intervention. Case Presentation: A case of CVST masqueraded as high altitude cerebral edema (HACE) at 6700 m/22000 ft in Karakoram Himalayas. Atypical oligosymptomatic presentation along with terrain, weather, and communication restrictions complicated diagnosis and management, leading to demise. CVST, confirmed on autopsy, was not associated with any pre-existing risk factors. Conclusion: CVST at extreme altitude can occur spontaneously due to prolonged hypobaric hypoxia which can precipitate thrombosis through capillary damage, haemoconcentration, and a hypercoagulable state.