What does the extralumial air appears contiguous with the rectum mean ??

Bowel perforation?: Within the abdominal/pelvic cavity, the only normal place to find air is within the bowel lumen. Unless there has been very recent surgery or penetrating trauma, "extra luminal" air, air outside the bowel, usually implies a bowel perforation. In your case it sounds as though they believe it is at the rectum. Speak to your doctor about this as soon as possible.