For anyone wondering what this skull would look like with hair and skin on it. Congenital hydrocephalus, or “water on the brain”, was an intractable condition until the 20th century, when effective shunts were developed that could alleviate the pressure within the skull. “Internal” in this case means that the cerebrospinal fluid is building up within the ventricles of the brain. In external hydrocephalus, the CSF builds up around the outside of the brain, in the subarachnoid region.
1817 illustration by French physician Jean Louis Alibert.