"There was no confusion, facial weakness, visual or speech disturbance", the doctors wrote.
Doctors treating an 84-year-old Irish man, who went to the emergency room with complaints of feeling unsteady over the past several months, were shocked to find he was missing the right frontal lobe of his brain, reports said.
But a head CT and MRI scan revealed that where the right frontal lobe of his brain should be, the patient had only a large, empty void, called pneumocephalus. Those types of cavities are typically found in patients who've had brain surgery or various types of infections.
When doctors were told that neither of these scenarios applied to the patient, they were "left very curious as to the cause of these findings", Brown said.
Finlay Brown, a physician working in the emergency department at Causeway Hospital in Coleraine, Northern Ireland, at the time, remembers reviewing the brain-imaging scans with the rest of the staff.
The air cavity was also reported as a "rare cause" of a small stroke the man had suffered, which had likely led to the left-side weakness and other symptoms that prompted the man's hospital visit, according to the BMJ Case Reports study.
"To find a pocket of this size in an organized fashion was extremely uncommon, with very few documented cases found while I was researching for writing up the case report", Brown added. Brown told The Washington Post in an email. The emergence of air in a brain cranium following a major surgery is also commonly attributed to this condition.
Generally, pneumocephalus appear after brain surgery, sinus infections or head and facial injuries.
A scan of the man's skull shows the air pocket (the black space) where part of his brain should be.
After medics made the discovery, the patient was then transferred to Antrim Area Hospital for an MRI scan of his head, which confirmed doctor theories that it was an air pocket but also revealed a large osteoma - a benign, bone tumor.
Staff chose to give the man a CT and MRI scan, and it was then that they saw the blank where some of his brain should have been, measuring 3.5 inches long.
"From speaking to the specialists, it seems it has been progressing insidiously over months to years", Brown said. In order to revert it, the patient had two surgeries - one to remove the tumor and the other to decompress the air pocket in the brain. However, due to the associated risks, the man declined the offer.
"The left-sided weakness was noted to have resolved on follow-up 12 weeks later and he remained well", the authors conclude in the published report.
Brown and his co-authors, however, emphasized in their paper symptoms like these should always be thoroughly explored and examined.