Left-sided colonic lesions obstruct sooner, because the left colon is narrower and its stool is harder. Right-sided tumors tend to show up with anaemia instead.

• C is false: in LBO vomiting is late (constipation and distension come early).
• D is false: an apple-core lesion means colorectal carcinoma. Volvulus gives a bird's-beak sign.
• B is false: most LBO is due to cancer, which needs definitive treatment.