The remarkable cause of an 84-year-old man’s numerous minor symptoms when he came to the emergency room shocked his doctors.

It is not unusual for a man of such advanced years to experience muscle weakness or loss of balance, nor is it especially notable for them to suffer falls. But when the frequency of all three became concerning, the unnamed Irishman came to Causeway Hospital in Coleraine, Northern Ireland, for answers.

Dr. Finlay Brown recalls the unique experience: “He was otherwise fit and well, independent with physical activities of daily living … and lived at home with his wife and two sons.” But after a CAT scan and MRI, it became immediately apparent that the man’s case was almost unprecedented; there was nothing but empty space where a large part of his brain should have been.

Most of the patient’s right frontal lobe was instead an empty pocket of air. Brown told the Washington Post that he and his colleagues were “very perplexed” by the images. In fact, the results were so extreme that the physicians involved at first thought that he had forgotten to disclose a past brain surgery or birth defect.

Pneumocephalus is a pressurized packet of air in the brain that almost always occurs after brain surgery, or in a much smaller sense from a serious sinus infection or head injury. Instead, the patient in question had developed a benign bone tumor, otherwise known as an osteoma, in his sinuses. It had been slowly eating through the base of his skull.

Every time the man coughed, sneezed, or even sniffed, he was adding air pressure to his brain through a sort of one-way valve through the tumorous opening. Gradually building air pressure had caused a small stroke that made muscles on the left side of his body weaken — fortunate, because it led him to the hospital where he was diagnosed.

The patient in question refused all treatment for the condition, choosing to avoid the almost inevitable complications of major brain surgery in the last years of his life. He was prescribed medication to prevent another stroke and continues on. It is unknown how long he will survive with such a condition because of its extreme rarity. “Unfortunately, as there are not many cases published, it is hard to know the exact prognosis,” Brown said.

Brown and colleague Djamil Vahidassr published their findings in BMJ Case Reports, telling LiveScience that they wanted to highlight “the importance of thorough investigation of even the most common of symptoms,” even among elderly patients who might otherwise be ignored.