Sorry to hear that your son is in hospital.
My son was rushed in April 09(not diagnosed with Crohns until November 09). His appendix was removed and histology reports indicated that he had appendicitis and peritonitis. I had hoped that the pains he had been experiencing were due to his appendix rumbling and that he would then be free of pain.
Now move forward to November 09, the Crohns was found in my son directly under his appendectomy scar !
So in his case he had two things going on however I did read somewhere that it appears that for whatever reason one appears to be related to the other.
Fingers crossed that he will be free of Crohns!