So all of this is what’s known based on the brief report from McCain’s office, which managed to spark a wave of armchair-theorizing from doctors. For example, in the Donald Trump subreddit, one user wrote in a popular post: “Fake news has EVERYTHING wrong. First off, I’m a physician. There are reports of John McCain having a ‘clot above his eye removed.’ I was curious. This is a very odd thing to say, as it doesn’t really happen … FACTS: They said it was a five centimeter clot. There isn’t enough room in the orbit (around the eyeball) for a five cm clot. They referred to it as a craniotomy, i.e., they went into his cranium. This has nothing to do with the neighboring orbit. Fake news is so garbage at medical reporting.”

Another doctor named Milton Wolf told his 19,500 twitter followers: “REALITY: Senator John McCain’s office successfully misled MSM [mainstream media] to report his brain surgery was ‘eye surgery.’ Clintonesque. Lost credibility … I think this demonstrates just how easily misled the press is—and then the public—by willfully granting blind trust to some sources.”

So, a note on intracranial bleeds and also on garbage medical reporting.

Within hours of McCain’s statement, The New York Times ran a detailed story with the headline, “McCain’s Surgery May Be More Serious Than Thought, Experts Say.” It remains unclear to whom “thought” refers, since the initial statement from McCain made clear that the senator had a new hole in his skull. Some headlines used the term “eye surgery,” but did imply that it was at least serious enough to derail the cornerstone of the Republican legislative agenda.

The Times went on to quote multiple neurosurgeons who contextualized and interpreted the meaning of the prior evening’s statement. Based on the information released by McCain and his caretakers at the Mayo Clinic in Arizona, the clot was most likely in the subdural space between his brain and the dural tissue that separates the cortex from the cranium.

Subdural hematomas are a fascinating and ever-more-common problem, given that they occur commonly in old age. Our brains shrink over time, and our skulls do not. This means that time creates space between brain and bone. The veins that drain the brain run along the bone and so must traverse the distance between the two. As that distance grows, those veins come under pressure. At the same time, the aging veins become more tenuous, and it’s not uncommon for them to tear and bleed slowly.

(U.S. National Library of Medicine / Argentina-Fernandez / Reuters)

Sometimes the accumulating blood presses on the brain causing vague and wide-ranging symptoms that can come on over long periods. Depending on how much pressure is exerted, and where, the symptoms can vary dramatically from one case to the next, so much so that neurologists refer to subdural hematomas as “the great imitator,” manifesting variously as headaches, transient weakness or paralysis, altered mental state, and dementia, among other symptoms.