CHICAGO — When it comes to MR scans of the men and women who scale mountains, there may be more than meets the eye.
New research shows that high-altitude cerebral edema (HACE), the end stage of severe acute mountain sickness — once thought to be reversible — causes microbleeding on the brain.
Michael Knauth, MD, PhD, presented the findings from a study aimed at detecting brain bleeds in survivors of HACE, comparing their MR results with survivors of other altitude-related illnesses.
His team theorized that hemosiderin deposits on the brain left by HACE-related hemorrhaging should cause enough of a magnetic disturbance to show up on an MR, but that differences in MR sensitivity might have been throwing readings off in T2-weighted imaging. For this reason, the team decided to use an alternative method, susceptibility-weighted imaging (or SWI), to look for HACE-related microbleeds that MR might have missed.
Knauth explained that Peter H. Hackett, MD’s work with MRIs of Mt. McKinley-area climbers in the 1990s set the stage for the investigation of HACE-related brain changes.
“He investigated climbers that were flown down or carried down from the mountain McKinley with HACE,” he said. “What he found was high-signal changes in the part of the brain we call the corpus callosum.”
Since the climbers with whom Hackett was able to follow up showed no signs of HACE afterwards, Hackett concluded that HACE was characterized by a reversible edema that liked to attack that part of the brain.
But, in the course of their own research, Knauth’s team encountered an outlier.
Namely, they came upon the case of a 50-year-old female patient who experienced HACE upon visiting the Andes Mountains. When her brain was scanned after the fact using SWI, microbleeds showed up as black dots on her brain. Hers marked the first case in which a living person was documented as having HACE-related microhemorrhages.
This led them to launch the current study based on a three-part hypothesis, all based on the assumption that the woman could not be the only HACE patient of her kind.
To counter this imbalanced detection during their study, the researchers used susceptibility-weighted imaging, the same kind of test used on the female HACE survivor. Following the success of a pilot study of six mountaineers, the team launched a study of 36 mountaineers: 10 HACE survivors, 11 severe AMS survivors, eight HAPE survivors and seven high-altitude mountaineers who lacked HACE, AMS and/or HAPE despite having made multiple expeditions sans supplemental oxygen.
“We performed a blood-sensitive sequence in all these subjects,” Knauth said. “Neuroradiologists were blinded to the mountaineers’ status.”
He and his research associates then scored the SWI readings as being positive for HACE, negative for HACE or questionable. Eight of out 10 HACE survivors, 10 out of 11 AMS survivors, seven out of eight HAPE survivors and five out of seven high-altitude survivors were correctly scored. Knauth pointed out that while the incorrect scores may have been legitimately wrong , the mountain-climbing attitude might have made study participants negligence to disclose all cases of HACE.
Researchers concluded that HACE is not fully reversible.
“There are changes to be seen years after a survived HACE,” Knauth said. “Microbeeds are found almost consistently and almost exclusively in the brains of HACE survivors, but not in the brains of other mountaineers who experience trouble at high altitudes.”
Knauth said that while the neuropsychological consequences of the microbleeds are still unclear, there is not data suggesting that they cause impairment.
Figure 1. The images show magnetic resonance (MR) slices through the brains of two mountaineers. The image on the left is from a mountaineer who climbed to altitudes above 7,000 meters, and the one on the right is from a mountaineer who survived a high altitude cerebral edema (HACE).
The arrows point to a brain structure which is called corpus callosum—it consists of densely packed nerve fibres connecting the two brain hemispheres. This part of the corpus callosum is normal in the left image, whereas in the right image (HACE survivor) it shows black spots representing multiple small hemorrhages (microhemorrhages). Courtesy RNSA.