Final answer:
The primary cause of colonic obstruction is colorectal cancer, which often arises from benign polyps; other causes include inflammatory conditions like ulcerative colitis.
Step-by-step explanation:
The number 1 cause of a colonic obstruction is colorectal cancer. This condition is often signaled by symptoms such as constipation or diarrhea, cramping, abdominal pain, and rectal bleeding. Most colon cancers originate from benign mucosal growths known as polyps; thus, cancer prevention focuses on the identification and removal of these polyps through procedures like colonoscopy. Other causes of colonic obstruction include inflammatory bowel diseases like ulcerative colitis, which is characterized by inflammation and ulcers in the colon and rectum, leading to symptoms like lower abdominal pain and bloody diarrhea. People with ulcerative colitis also have an increased risk of developing colon cancer.