After an especially tiring day or a serious lack of food, it’s not unusual to feel lightheaded. It is, however, unusual to discover that the cause of the lightheadedness is that your brain cavity is filled with literal air, which is what perplexed physicians described in a strange study in BMJ Case Reports on Monday. Scanning the brain of an 84-year-old man complaining he felt unsteady, they discovered a huge air pocket where part of his brain should be.

In the paper, titled “The man that lost (part of) his mind,” the physicians, led by Dr. Finlay Brown of Northern Ireland’s Causeway Hospital, present a series of scans showing a big black gap where you would expect a right frontal lobe. What is strangest is that the patient didn’t complain about much more than feeling unsteady and falling down a lot over the past few months, though he did start feeling weakness in his left arm and leg.

Nevertheless, Brown and his co-author, Dr. Djamil Vahidassr, note: “There was no confusion, facial weakness, visual or speech disturbance, and he was feeling otherwise well.”

brain scan air pocket
The man had an air pocket where his right frontal lobe should have been.

As they puzzled over the brain scans, they determined that the man had pneumocephalus, which is the medical term for “air (or gas) in the brain.” It’s a pretty common consequence of brain trauma or brain surgery. The thing is, this man had not experienced either of those things. Still, he had an air cavity that was about 3.5 inches at its greatest length.

The physicians determined that his air bubble was probably caused by a small, benign bone tumor that had formed in his frontal sinus. This little bump of bone is thought to have opened up a “one-way valve” in the cribriform plate (a wall between the nasal cavity and the brain), which allowed pressurized air to seep into the brain and stay there. Higher-pressure air — like that induced by sneezing and coughing — could have forced its way into the cavity more quickly, they note.

frontal sinus
The patient had a small bone tumor in his frontal sinus.

Here’s an MRI image of the man and his huge air pocket:

air pocket brain
A benign tumor by his nasal cavity opened up a "one-way valve" for air to leak into the brain cavity.

Though it looks dramatic, the air pocket is not especially life-threatening in most cases. One review of pneumocephalus, published in Surgical Neurology International in 2015, noted that air pockets usually get absorbed by the brain, though they can sometimes cause events like intracranial hypertension (high pressure) or impaired consciousness. In these cases, it’s crucial to remove the air in the brain, which is usually done by drilling a small hole to release the air. In this case, because the tumor was deemed to be the most likely cause of the air pocket, surgery could have been done to remove the tumor, but the patient declined because of his age.

As things stand, the biggest risk this man seems to face is having a secondary stroke (he had experienced a small one already), which is when one of the blood vessels leading to the brain bursts or gets blocked by a clot. Treatment included stroke-prevention medication and not much else, and in a few months the patient seemed to be doing just fine.

“The left-sided weakness was noted to have resolved on follow-up 12 weeks later and he remained well,” the researchers write, highlighting evidence that the human body, for all its faults, can withstand some strange things — and is often well equipped to heal itself.