Cure for hydrocephalus leads to loss of intelligence (5,5)
I believe the answer is:
brain drain
'loss of intelligence' is the definition.
(intelligent individuals leaving a country)
I don't understand the rest of the clue.
(Other definitions for brain drain that I've seen before include "Emigration of talent" , "Movement of highly skilled people" , "Migration of talent" , "Haemorrhaging of talent" , "Emigration of well-educated people" .)