Anal Fissure or Fissure-in-ano is a small crack or tear in the opening and lining of the anus. If you buy something through a link on this page, we may earn a small commission. An anal fissure may occur when you pass hard or large stools during a bowel movement. WHAT IS AN ANAL FISSURE? An anal fissure (fissure-in-ano) is a small, oval shaped tear in skin that lines the opening of the anus. What is an anal fissure? An anal fissure is a cut or tear occurring in the anus (the opening through which stool passes out of the body) that.