What radiological finding is characterized as an "apple core" lesion?

The "apple core" lesion is a specific radiological finding associated with colorectal cancer. This term describes the appearance of the lesion on barium enema studies or colonoscopy images, where the cancerous tissue causes a constriction and irregular narrowing of the bowel segment, resembling the shape of an apple core. This characteristic image results from the circumferential growth of the tumor, which leads to a localized narrowing of the intestinal lumen. Additionally, this type of lesion often presents in advanced cases of colorectal cancer, where there is a significant obstructive change in the bowel.

In contrast, gastric ulcers may present with different shapes and characteristics on imaging, often showing irregularities but not typically described as "apple core." Duodenal obstruction would manifest with different signs, such as dilation of upstream loops rather than this specific lesion morphology. Pseudomembranous colitis, while it can show thickened colonic walls, would not present a distinctive "apple core" shape in imaging studies. The defining feature of the "apple core" appearance solidifies its association specifically with colorectal malignancy, distinguishing it from other gastrointestinal issues.