If you ever feel you're starting to lose your mind, it could be worth checking you don't have a gaping great hole in your head.
This was the shocking discovery of an elderly Irish man after he complained of weakness in his arms and legs.
After suffering a number of falls the 84-year-old arrived in the emergency room at a hospital in Coleraine, Northern Ireland and was sent for CT and MRI scans.
Results showed an astonishing gap in the space where his frontal lobe should have been.
Yet a doctor's summary of the man's case published in medical journal BMJ reported that he showed no signs of confusion, facial weakness, visual or speech disturbance.
"He was otherwise fit and well, independent with physical activities of daily living… and lived at home with his wife and two sons," the report said.
Finlay Brown, a physician working at the hospital, told the Washington Post the doctors were very perplexed by the images.
In fact they even wondered if the man had forgotten to disclose elements of his medical history.
Dr Brown said it turned out the man had pneumocephalus, also known as pressurised air cavity, meaning the presence of air in the cranium.
"In my research for writing the case report I wasn't able to find very many documented cases of a similar nature to this one," Dr Brown told the Washington Post.
It's cause was likely an osteoma, or benign bone tumour, something which had formed in the man's sinus, Dr Brown said.
This had enabled a "one-way valve effect" that had gradually carved the cranial air cavity, he said.
Dr Brown also said the condition is found in nearly 100 percent of cases after brain surgery.
While the man could have undergone surgeries he declined due to his age and other health factors.
However The Washington Post reported that the man is doing well and has even reported he no longer feels any weakness.