High Altitude Climbers at Risk for Brain Hemorrhage

New magnetic resonance imaging (MRI) research has demonstrated that mountain climbers who experience a specific type of high-altitude illness called high altitude cerebral edema (HACE) have evidence of brain bleeding years after the initial incident.

The new research was presented in November 2012 at the annual meeting of the Radiological Society of North America (RSNA), held in Chicago (IL, USA). HACE is a severe and frequently lethal disorder that can affect mountain climbers, skiers, hikers, and travelers at high altitudes—typically higher than 2,300 meters.

HACE results from swelling of brain tissue caused by leakage of fluids from the capillaries. Symptoms include headache, loss of coordination, and decreasing levels of consciousness. “HACE is a life-threatening condition,” said Michael Knauth, MD, PhD, from the University Medical Center’s department of neuroradiology (Gottingen, Germany). “It usually happens in a hostile environment where neither help nor proper diagnostic tools are available.”

Dr. Knauth and colleagues from the University Hospitals in Gottingen and Heidelberg (Germany), compared brain MRI scans among four groups of mountaineers: climbers with a history of high altitude illness; climbers with well documented episodes of HACE; climbers with a history of severe acute mountain sickness (AMS); and climbers with a history of isolated high altitude pulmonary edema (HAPE), a life-threatening accumulation of fluid in the lungs that occurs at high altitudes. Two neuroradiologists evaluated the brain MRI findings without knowing the status of the mountaineers and assigned a score based on the number and location of any microhemorrhages. “In most cases, these microhemorrhages are so small that they are only visible with a special MRI technique called susceptibility-weighted imaging,” Dr. Knauth said. “With this technique, the microhemorrhages are depicted as little black spots.”

The MRI scans revealed brain microhemorrhages almost exclusively in HACE survivors. Of the 10 climbers with a history of HACE, eight had evidence of microhemorrhages on MRI. The other two had uncertain results. Only two of the remaining 26 climbers were positive for microhemorrhages. “It was previously thought that HACE did not leave any traces in the brains of survivors,” Dr. Knauth said. “Our studies show that this is not the case. For several years after, microhemorrhages or microbleeds are visible in the brains of HACE survivors.”

Survivors of the most clinically severe cases of HACE had the most noticeable traces of microhemorrhages on MRI scans. The hemorrhages were found chiefly in the corpus callosum, the thick band of nerve fibers that connects the left and right halves of the brain, and revealed a characteristic distribution different from other vascular diseases such as vasculitis (blood vessel inflammation). “The distribution of microhemorrhages is a new and sensitive MRI sign of HACE and can be detected years after HACE,” Dr. Knauth said. “We will further analyze our clinical and MRI data on patients with acute mountain sickness, which is thought to be a precursor of HACE.”

Meanwhile, Dr. Knauth does not believe HACE survivors need to give up climbing. “We cannot give such a strong recommendation,” he said. “However, mountaineers who have already experienced HACE once should acclimatize to the altitude very slowly.”

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