A 6-year-old boy is brought to the office with 6 months of episodic belly pain. The mother states that the child complains mostly in the afternoon and evening.  The pain usually lasts a few minutes and can be severe.  Bowel movements have been irregular. Otherwise, the child is healthy, growing and developing normally, and is in first grade. On examination, vital signs and growth parameters are normal. On questioning the child as to the specific location of her pain, he points to the umbilicus. On deep palpation there is a firm mass in the left lower quadrant; it is non-tender and the abdomen is otherwise soft. The rest of the examination is normal.