Luminal narrowing refers to the reduction in the diameter of a tubular structure within the body, such as blood vessels or the gastrointestinal tract, often due to pathological processes like inflammation, fibrosis, or atherosclerosis. This condition is clinically significant as it can lead to impaired blood flow or obstructed passage of contents, resulting in symptoms like angina or bowel obstruction. A key example is coronary artery disease, where narrowing can precipitate myocardial ischaemia.