High-Altitude Cerebral Edema Evaluated With Magnetic Resonance Imaging

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Abstract
HIGH-ALTITUDE CEREBRAL edema (HACE) is a potentially fatal neurologic syndrome that develops over hours or days in persons with acute mountain sickness (AMS) or high-altitude pulmonary edema (HAPE).1-3 This type of high-altitude illness typically presents with altered mental status, ataxia, and progressive neurologic deterioration and is considered to be the end stage of AMS. Although hypoxia is the triggering stimulus, the exact pathophysiology of HACE, as well as AMS, is still not known. In the framework of the 2 general types of cerebral edema,4,5 authors have postulated that HACE may be either cytotoxic (intracellular, due to cellular swelling),2,6 vasogenic (extracellular, due to blood-brain barrier leakage),1,7,8 or a combination of the 2.9 The distinction has important implications not only for prevention and treatment but also for determining the direction of future research on the basic mechanisms of altitude illness. Brain edema found on autopsy has been so severe and global that it has not been helpful in elucidating the initial pathophysiology.1,10 One brain biopsy done to exclude other diagnoses reported microscopic evidence of "edematous brain" without further distinction.1 Work with a sheep model of altitude illness that showed extravasation of Evans blue dye in the brain suggested vasogenic edema.11