A fissure consists of a crack or tear in the vertical axis of the inner lining of the anal canal just above the anal verge.

Initially it is superficial but may deepen to reach the underlying muscle fibers.

Fissures usually occur in the posterior midline.

Fissures are often associated with secondary changes which may include a skin tag (also known as a sentinel pile though it is not actually ‘piles’), hypertrophied anal papilla, and relative anal stenosis secondary to spasm of the muscle sphincter