Apple core sign is a characteristic finding in stenosing annular colorectal carcinoma. The typical appearance is attributed to constriction of lumen. It is also known as ‘napkin sign’. In addition to colorectal carcinoma, apple core sign may also be present in case of Crohn’s disease, ulcerative colitis, ischemic colitis, lymphoma, tuberculosis, and villous adenoma. Reference: https://radiopaedia.org/articles/apple-core-sign-colon-1 Image via: https://www.researchgate.net/publication/38094336_Apple-core_lesion_of_the_colon_A_case_report/figures?lo=1&utm_source=google&utm_medium=organic