Understanding Bladder Spasms in Children: Causes and Relief

Question
My 5 year old little brother was rushed to the ER the other night do to abdominal pain. There was a not just under the surface of his stomach and perfectly visible. When we arrived to the hospital, they informed us that it was a bladder "spasm". They said all they did was have him urinate and he was fine. He was tested for an infection and there wasn't any. I have searched everywhere online for a clue as to what one is and how he managed to suffer from one. I was wondering if you could tell me what a bladder spasm is and what causes them.  

Answer
I am not sure I understand the term bladder spasm.... I would not expect that to be found in a 5 year old boy.  Whatever he had improved.... but it was only coincidence that it improved when he urinated..... so, my thought is something else was the problem.... either it is gone now or it will re-occur, but I wouldn't write it off as "bladder spasm."