I agree with the others that you need to get him back to the vet or emergency vet asap. My cat Cirrus had the operation and it was successful and he's been fine ever since. He's on the Hills Prescription c/d diet. I remember my vet telling me that without the operation, it would take a few months for the new food to dissolve the crystals. Good luck and please keep us updated.

Here's a link to the surgery which is called perineal urethrostomy
http://consumer.vetmedcenter.com/con...FL1EM.xml&dt=A.