What Causes Hydrocephalus In Brain?

My husband was recently diagnosed with communicating hydrocephalus and will be having surgery soon. He had a CT scan done and read 3 weeks prior to having a second MRI done which found the fluid. The radiologist read the first CT wrong and reported no findings and everything normal. But on a second view of the same film, from a surgeon confirmed there was indeed enlargement of the ventricles and they were wrong. Could the delay from the 1st CT that was read wrong to now 3 weeks later made his condition any worse???