Apple core sign | Radiology Signs

Answer: The apple core sign, also known as the napkin ring sign, is most frequently caused by a stenosing annular colorectal carcinoma; however, other etiologies include lymphoma, chlamydia infection, and post-radiation therapy from radiosurgery. The classic appearance is that of a short, irregular, circumferential colonic stricture with overhanging margins and ulceration. Clinically, patients may present with abdominal pain, weight loss, diarrhea (which may be bloody), and iron deficiency anemia. Confirmation and differentiation usually require colonoscopy and histological assessment.

Why is it called so?

The sign is named for its visual resemblance to the core of an apple after the flesh has been eaten—a short segment of marked luminal stenosis with abrupt, “shouldered” margins mimics the appearance of the remaining central core, hence the term apple core sign. The term napkin ring sign was coined by Russell Carman to describe a similar circumferential narrowing. Both terms highlight the concentric narrowing with overhanging edges.

Pathophysiology

The apple core sign arises due to eccentric thickening of the colonic wall—typically by an infiltrating neoplasm—leading to severe luminal stenosis. The tumor grows circumferentially, destroying the mucosa and creating ulceration, with the remaining intact margins appearing as “shoulders” on imaging. This results in a narrowed, eccentric, irregular lumen often measuring 3–6 cm in length. Inflammatory and infectious processes may produce similar morphology by causing transmural inflammation, fibrosis, and stricturing.

Alternative names: Napkin ring sign (bowel).

Other associated named signs: None commonly cited in the literature for this specific pathology.