Abnormal small intestinal mucosa morphology Thinned small intestinal mucosa 2024-02-20T09:54:55Z Abrnormal reduction in the height of the mucosa of the small intestine. The mucosa is arranged in regular circular folds (the circular valves of Kerckrin), the mucosal surface is covered with small projections called villi, which are slender, about 1.5-2 mm long projections of the mucosa into the lumen. In between the villi are the crypts. This term refers to a pathological thinning of these structures.