A parasitic tapeworm 10cm long lived in the brain of a British man for four years before doctors discovered it.
The 50-year-old first visited doctors in 2008 suffering from headaches, seizures, memory loss and a changed sense of smell.
An MRI scan showed a cluster of what appeared to be lesions, but specialists were baffled. They were more surprised when brain scans over four years showed the anomaly had travelled 5cm through tissue.
Doctors at St Thomas' Hospital in London took biopsies and tested the man for diseases including HIV, lyme disease and syphilis. However in 2012 they were amazed to find that amid his brain tissue was a "10cm ribbon-shaped larval worm". Once diagnosed, the man was treated easily with drugs and has recovered.
The tapeworm Spirometra erinaceieuropaei has been reported only 300 times worldwide since 1953 and has never been seen before in Britain.