The NIH team, led by Avindra Nath, used a high-powered magnetic resonance imaging (MRI) scanner (up to 10 times as sensitive as a typical MRI) to examine postmortem brain tissue from 19 patients. They ranged in age from 5 to 73, and some had preexisting conditions, such as diabetes, obesity, and cardiovascular disease.
The team focused on the brain’s olfactory bulb that controls our ability to smell and the brainstem, which regulates breathing and heart rate. Based on earlier evidence, both areas are thought to be highly susceptible to COVID-19.
Indeed, the MRI images revealed in both regions an unusual number of bright spots, a sign of inflammation. They also showed dark spots, which indicate bleeding. A closer look at the bright spots showed that tiny blood vessels in those areas were thinner than normal and, in some cases, leaked blood proteins into the brain. This leakage appeared to trigger an immune reaction that included T cells from the blood and the brain’s scavenging microglia. The dark spots showed a different pattern, with leaky vessels and clots but no evidence of an immune reaction.
While those findings are certainly interesting, perhaps equally noteworthy is what Nath and colleagues didn’t see in those samples. They could find no evidence in the brain tissue samples that SARS-CoV-2 had invaded the brain tissue. In fact, several methods to detect genetic material or proteins from the virus all turned up empty.
