Colon stricture

My perfectly healthy 17 year old son today had a colonoscopy and a Endo completed by our family Ped GI. My son is in perfect shape as he is a D1 College Football Player. Never ever any trouble with his GI tract. We chose to have this procedure done due to his weight loss over the last 3 months..we played at 160 and dropped to 150. HE WORKS OUT ALL THE TIME. But just is not gaining any weight. So the GI put our son on periaxil aka a antihistamine pill. Since taking this dosage he has gained 6 pounds in 10 days and remarks how great he feels now... Well to be preventive our GI and my wife and son and I agreed to ruling out everything else before he heads out back to school. Well today our son has his colo and Endo done. The Endo was great and showed nothing...BUT the colo presented a stricture at the top end corner where the middle intestine and he could not make the turn. Everything to that point is fine BUT our GI freaked us out be ause he could not make the 90 degree turn to complete a full colo exam. No our son has never ever had pain, never passed blood, has daily void and evac normal stool. In perfect health. Has been examed prior to this colo and had all blood work done for Celiac etc. nothing shows up in the blood work. So tomorrow our son is having a barium enema done and a Cat Scan and X-rays completed to visualize what is going on with why he could not make the 90 degree bed. We are all worried sick as our son is a picture of health and never sick. What causes a stricture ? Are there different sizes of colo scopes ... IE..Small or medium or large. Can these strictures be enlarged by the " balloon " process? Please if anyone out there has any comments on this we really want to hear from you. Thank you