In a 2007, scientists described an incredible medical oddity on a 44 years old man. This french man live an entirely normal life with tiny brain. 

The large black space shows the fluid that replaced much of the patient’s brain (left). For comparison, the images (right) show a typical brain without any abnormalities. 

The man went into hospital after he experienced weakness in his left leg for two weeks. Scientists were quite surprised when they took scans of his brain and found a huge fluid-filled chamber. The scans showed that the man had a “massive enlargement of the lateral, third, and fourth ventricles, a very thin cortical mantle and a posterior fossa cyst,” researchers noted in the study. In short, while fluid normally circulates throughout the brain, it’s regularly drained. 

But instead of draining the fluid into the circulatory system, the fluid in this man’s brain built up. Eventually, the accumulation of fluid resulted in only a tiny amount of actual brain material.  The man’s medical history showed that he had to get a shunt inserted into his head as an infant to get rid of the buildup of fluid on the brain, known as hydrocephalus.

Hydrocephalus is an abnormal accumulation of cerebrospinal fluid (CSF) in the ventricles of the brain and can be caused by an impaired flow of cerebrospinal fluid, reabsorption, or excessive production of CSF. Hydrocephalus is colloquially termed as "water on the brain" and is of medical importance.

The shunt was eventually removed when at age 14, he complained of left leg weakness and some unsteadiness. The man went on to live a normal life and he got married and had two children.

Brain adaptation

These cases show not only the adaptability and resilience of the human brain, but also how little we know about one of our most important organs. Cases like this force neuroscientists to rethink how we view the brain, particularly what functions different regions have and how the brain adapts when these regions become damaged.